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  • Lunar and Planetary Science and Exploration  (3,706)
  • Geophysics  (1,333)
  • 2020-2023  (1)
  • 2000-2004  (5,038)
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  • 1
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    3-D seismic interpretation with deep learning: a set of Python tutorials (2021)
    GFZ Data Services
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    Publication Date: 2022-02-24
    Description: Abstract
    Description: Here we are sharing our code, tutorials and examples used to interpret geological structures (e.g. faults, salt bodies and horizones) in 2-D and/or 3-D seismic reflection data using deep learning. The repository is organised in a series of tutorials (Jupyter notebooks) with increasing degree of difficulty. We show step-by-step how to: (1) load seismic data, (2) train a model and (3) apply the model to map different geological structures. You can find a few visual examples on our poster and more technical details in our preprint.
    Keywords: Seismic reflection data ; Seismic interpretation ; Machine learning ; Deep learning ; Geophysics ; EARTH SCIENCE ; EARTH SCIENCE 〉 OCEANS 〉 MARINE GEOPHYSICS ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS
    Type: Software , Software
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  • 2
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    Robots and humans: synergy in planetary exploration (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: How will humans and robots cooperate in future planetary exploration? Are humans and robots fundamentally separate modes of exploration, or can humans and robots work together to synergistically explore the solar system? It is proposed that humans and robots can work together in exploring the planets by use of telerobotic operation to expand the function and usefulness of human explorers, and to extend the range of human exploration to hostile environments. Published by Elsevier Ltd.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Acta astronautica (ISSN 0094-5765); Volume 55; 12; 985-90
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  • 3
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    Solar particle events observed at Mars: dosimetry measurements and model calculations (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: During the period from March 13, 2002 to mid-September, 2002, six solar particle events (SPE) were observed by the MARIE instrument onboard the Odyssey Spacecraft in Martian Orbit. These events were observed also by the GOES 8 satellite in Earth orbit, and thus represent the first time that the same SPE have been observed at these separate locations. The characteristics of these SPE are examined, given that the active regions of the solar disc from which the event originated can usually be identified. The dose rates at Martian orbit are calculated, both for the galactic and solar components of the ionizing particle radiation environment. The dose rates due to galactic cosmic rays (GCR) agree well with the HZETRN model calculations. Published by Elsevier Ltd on behalf of COSPAR.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Advances in space research : the official journal of the Committee on Space Research (COSPAR); Volume 33; 12; 2215-8
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  • 4
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    Planetary science. Looking into the giant planets (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: No abstract available
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 305; 5689; 1414-5
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  • 5
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    Meteor wake in high frame-rate images--implications for the chemistry of ablated organic compounds (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Extraterrestrial organic matter may have been chemically altered into forms more ameanable for prebiotic chemistry in the wake of a meteor after ablation. We measured the rate of cooling of the plasma in the meteor wake from the intensity decay just behind a meteoroid by freezing its motion in high frame-rate 1000 frames/s video images, with an intensified camera that has a short phosphor decay time. Though the resulting cooling rate was found to be lower than theoretically predicted, our calculations indicated that there would have been insufficient collisions to break apart large organic compounds before most reactive radicals and electrons were lost from the air plasma. Organic molecules delivered from space to the early Earth via meteors might therefore have survived in a chemically altered form. In addition, we discovered that relatively small meteoroids generated far-ultraviolet emission that is absorbed in the immediate environment of the meteoroid, which may chemically alter the atmosphere over a much larger region than previously recognized.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Astrobiology (ISSN 1531-1074); Volume 4; 1; 95-108
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  • 6
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    Hydrogen emission in meteors as a potential marker for the exogenous delivery of organics and water (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We detected hydrogen Balmer-alpha (H(alpha)) emission in the spectra of bright meteors and investigated its potential use as a tracer for exogenous delivery of organic matter. We found that it is critical to observe the meteors with high enough spatial resolution to distinguish the 656.46 nm H(alpha) emission from the 657.46 nm intercombination line of neutral calcium, which was bright in the meteor afterglow. The H(alpha) line peak stayed in constant ratio to the atmospheric emissions of nitrogen during descent of the meteoroid. If all of the hydrogen originates in the Earth's atmosphere, the hydrogen atoms are expected to have been excited at T = 4400 K. In that case, we measured an H(2)O abundance in excess of 150 +/- 20 ppm at 80-90 km altitude (assuming local thermodynamic equilibrium in the air plasma). This compares with an expected 〈20 ppm from H(2)O in the gas phase. Alternatively, meteoric refractory organic matter (and water bound in meteoroid minerals) could have caused the observed H(alpha) emission, but only if the line is excited in a hot T approximately 10000 K plasma component that is unique to meteoric ablation vapor emissions such as Si(+). Assuming that the Si(+) lines of the Leonid spectrum would need the same hot excitation conditions, and a typical [H]/[C] = 1 in cometary refractory organics, we calculated an abundance ratio [C]/[Si] = 3.9 +/- 1.4 for the dust of comet 55P/Tempel-Tuttle. This range agreed with the value of [C]/[Si] = 4.4 measured for comet 1P/Halley dust. Unless there is 10 times more water vapor in the upper atmosphere than expected, we conclude that a significant fraction of the hydrogen atoms in the observed meteor plasma originated in the meteoroid.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Astrobiology (ISSN 1531-1074); Volume 4; 1; 123-34
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  • 7
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    Jupiter's atmospheric composition from the Cassini thermal infrared spectroscopy experiment (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of acetylene and ethane, the latter a tracer of atmospheric motion; observations of unexpected spatial distributions of carbon dioxide and hydrogen cyanide, both considered to be products of comet Shoemaker-Levy 9 impacts; characterization of the morphology of the auroral infrared hot spot acetylene emission; and a new evaluation of the energetics of the northern auroral infrared hot spot.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 305; 5690; 1582-6
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  • 8
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    First Atmospheric Science Results from the Mars Exploration Rovers Mini-TES (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Thermal infrared spectra of the martian atmosphere taken by the Miniature Thermal Emission Spectrometer (Mini-TES) were used to determine the atmospheric temperatures in the planetary boundary layer and the column-integrated optical depth of aerosols. Mini-TES observations show the diurnal variation of the martian boundary layer thermal structure, including a near-surface superadiabatic layer during the afternoon and an inversion layer at night. Upward-looking Mini-TES observations show warm and cool parcels of air moving through the Mini-TES field of view on a time scale of 30 seconds. The retrieved dust optical depth shows a downward trend at both sites.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 306; 5702; 1750-3
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  • 9
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    A space radiation shielding model of the Martian radiation environment experiment (MARIE) (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The 2001 Mars Odyssey spacecraft was launched towards Mars on April 7, 2001. Onboard the spacecraft is the Martian radiation environment experiment (MARIE), which is designed to measure the background radiation environment due to galactic cosmic rays (GCR) and solar protons in the 20-500 MeV/n energy range. We present an approach for developing a space radiation-shielding model of the spacecraft that includes the MARIE instrument in the current mapping phase orientation. A discussion is presented describing the development and methodology used to construct the shielding model. For a given GCR model environment, using the current MARIE shielding model and the high-energy particle transport codes, dose rate values are compared with MARIE measurements during the early mapping phase in Mars orbit. The results show good agreement between the model calculations and the MARIE measurements as presented for the March 2002 dataset. c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Advances in space research : the official journal of the Committee on Space Research (COSPAR); Volume 33; 12; 2219-21
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  • 10
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    Overview of the Martian radiation environment experiment (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Space radiation presents a hazard to astronauts, particularly those journeying outside the protective influence of the geomagnetosphere. Crews on future missions to Mars will be exposed to the harsh radiation environment of deep space during the transit between Earth and Mars. Once on Mars, they will encounter radiation that is only slightly reduced, compared to free space, by the thin Martian atmosphere. NASA is obliged to minimize, where possible, the radiation exposures received by astronauts. Thus, as a precursor to eventual human exploration, it is necessary to measure the Martian radiation environment in detail. The MARIE experiment, aboard the 2001 Mars Odyssey spacecraft, is returning the first data that bear directly on this problem. Here we provide an overview of the experiment, including introductory material on space radiation and radiation dosimetry, a description of the detector, model predictions of the radiation environment at Mars, and preliminary dose-rate data obtained at Mars. c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Advances in space research : the official journal of the Committee on Space Research (COSPAR); Volume 33; 12; 2204-10
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  • 11
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    Lunar precursor missions for human exploration of Mars--III: studies of system reliability and maintenance (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Discussions of future human expeditions into the solar system generally focus on whether the next explorers ought to go to the Moon or to Mars. The only mission scenario developed in any detail within NASA is an expedition to Mars with a 500-day stay at the surface. The technological capabilities and the operational experience base required for such a mission do not now exist nor has any self-consistent program plan been proposed to acquire them. In particular, the lack of an Abort-to-Earth capability implies that critical mission systems must perform reliably for 3 years or must be maintainable and repairable by the crew. As has been previously argued, a well-planned program of human exploration of the Moon would provide a context within which to develop the appropriate technologies because a lunar expedition incorporates many of the operational elements of a Mars expedition. Initial lunar expeditions can be carried out at scales consistent with the current experience base but can be expanded in any or all operational phases to produce an experience base necessary to successfully and safely conduct human exploration of Mars. Published by Elsevier Ltd.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Acta astronautica (ISSN 0094-5765); Volume 55; 3-9; 773-80
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  • 12
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    Deep space environments for human exploration (2004)
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    Publication Date: 2011-08-24
    Description: Mission scenarios outside the Earth's protective magnetic shield are being studied. Included are high usage assets in the near-Earth environment for casual trips, for research, and for commercial/operational platforms, in which career exposures will be multi-mission determined over the astronaut's lifetime. The operational platforms will serve as launching points for deep space exploration missions, characterized by a single long-duration mission during the astronaut's career. The exploration beyond these operational platforms will include missions to planets, asteroids, and planetary satellites. The interplanetary environment is evaluated using convective diffusion theory. Local environments for each celestial body are modeled by using results from the most recent targeted spacecraft, and integrated into the design environments. Design scenarios are then evaluated for these missions. The underlying assumptions in arriving at the model environments and their impact on mission exposures within various shield materials will be discussed. Published by Elsevier Ltd on behalf of COSPAR.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Advances in space research : the official journal of the Committee on Space Research (COSPAR); Volume 34; 6; 1281-7
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  • 13
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    Meteors do not break exogenous organic molecules into high yields of diatomics (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Meteoroids that dominate the Earth's extraterrestrial mass influx (50-300 microm size range) may have contributed a unique blend of exogenous organic molecules at the time of the origin of life. Such meteoroids are so large that most of their mass is ablated in the Earth's atmosphere. In the process, organic molecules are decomposed and chemically altered to molecules differently from those delivered to the Earth's surface by smaller (〈50 microm) micrometeorites and larger (〉10 cm) meteorites. The question addressed here is whether the organic matter in these meteoroids is fully decomposed into atoms or diatomic compounds during ablation. If not, then the ablation products made available for prebiotic organic chemistry, and perhaps early biology, might have retained some memory of their astrophysical nature. To test this hypothesis we searched for CN emission in meteor spectra in an airborne experiment during the 2001 Leonid meteor storm. We found that the meteor's light-emitting air plasma, which included products of meteor ablation, contained less than 1 CN molecule for every 30 meteoric iron atoms. This contrasts sharply with the nitrogen/iron ratio of 1:1.2 in the solid matter of comet 1P/Halley. Unless the nitrogen content or the abundance of complex organic matter in the Leonid parent body, comet 55P/Tempel-Tuttle, differs from that in comet 1P/Halley, it appears that very little of that organic nitrogen decomposes into CN molecules during meteor ablation in the rarefied flow conditions that characterize the atmospheric entry of meteoroids approximately 50 microm-10 cm in size. We propose that the organics of such meteoroids survive instead as larger compounds.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Astrobiology (ISSN 1531-1074); Volume 4; 1; 67-79
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  • 14
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    The mass and speed dependence of meteor air plasma temperatures (2004)
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    Publication Date: 2011-08-24
    Description: The speed and mass dependence of meteor air plasma temperatures is perhaps the most important data needed to understand how small meteoroids chemically change the ambient atmosphere in their path and enrich the ablated meteoric organic matter with oxygen. Such chemistry can play an important role in creating prebiotic compounds. The excitation conditions in various air plasma emissions were measured from high-resolution optical spectra of Leonid storm meteors during NASA's Leonid Multi-Instrument Aircraft Campaign. This was the first time a sufficient number and range of temperature measurements were obtained to search for meteoroid mass and speed dependencies. We found slight increases in temperature with decreasing altitude, but otherwise nearly constant values for meteoroids with speeds between 35 and 72 km/s and masses between 10(-5) g and 1 g. We conclude that faster and more massive meteoroids produce a larger emission volume, but not a higher air plasma temperature. We speculate that the meteoric plasma may be in multiphase equilibrium with the ambient atmosphere, which could mean lower plasma temperatures in a CO(2)-rich early Earth atmosphere.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Astrobiology (ISSN 1531-1074); Volume 4; 1; 81-94
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  • 15
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    Search for the OH (X(2)Pi) Meinel band emission in meteors as a tracer of mineral water in comets: detection of N(2)(+) (A-X) (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report the discovery of the N(2)(+) A-X Meinel band in the 780-840 nm meteor emission from two Leonid meteoroids that were ejected less than 1000 years ago by comet 55P/Tempel-Tuttle. Our analysis indicates that the N(2)(+) molecule is at least an order of magnitude less abundant than expected, possibly as a result of charge transfer reactions with meteoric metal atoms. This new band was found while searching for rovibrational transitions in the X(2)Pi electronic ground state of OH (the OH Meinel band), a potential tracer of water bound to minerals in cometary matter. The electronic A-X transition of OH has been identified in other Leonid meteors. We did not detect this OH Meinel band, which implies that the excited A state is not populated by thermal excitation but by a mechanism that directly produces OH in low vibrational levels of the excited A(2)Sigma state. Ultraviolet dissociation of atmospheric or meteoric water vapor is such a mechanism, as is the possible combustion of meteoric organics.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Astrobiology (ISSN 1531-1074); Volume 4; 1; 109-21
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  • 16
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    A SIFT ion-molecule study of some reactions in Titan's atmosphere. reactions of N(+), N(2)(+), and HCN(+) with CH(4), C(2)H(2), and C(2)H(4) (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The results of a study of the ion-molecule reactions of N(+), N(2)(+), and HCN(+) with methane, acetylene, and ethylene are reported. These studies were performed using the FA-SIFT at the University of Canterbury. The reactions studied here are important to understanding the ion chemistry in Titan's atmosphere. N(+) and N(2)(+) are the primary ions formed by photo-ionization and electron impact in Titan's ionosphere and drive Titan's ion chemistry. It is therefore very important to know how these ions react with the principal trace neutral species in Titan's atmosphere: Methane, acetylene, and ethylene. While these reactions have been studied before the product channels have been difficult to define as several potential isobaric products make a definitive answer difficult. Mass overlap causes difficulties in making unambiguous species assignments in these systems. Two discriminators have been used in this study to resolve the mass overlap problem. They are deuterium labeling and also the differences in reactivities of each isobar with various neutral reactants. Several differences have been found from the products in previous work. The HCN(+) ion is important in both Titan's atmosphere and in the laboratory.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Journal of the American Society for Mass Spectrometry (ISSN 1044-0305); Volume 15; 8; 1148-55
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  • 17
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    Surface Penetrating Radar Simulations for Europa (2004)
    In:  CASI
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    Publication Date: 2004-10-05
    Description: The space environment above the icy surface of Europa is a source of radio noise in this frequency range from natural sources in the Jovian magnetosphere. The ionospheric and magnetospheric plasma environment of Europa affects propagation of transmitted and return signals between the spacecraft and the solid surface in a frequency-dependent manner. The ultimate resolution of the subsurface sounding measurements will be determined, in part, by a capability to mitigate these effects. We discuss an integrated multi-frequency approach to active radio sounding of the Europa ionospheric and local magnetospheric environments, based on operational experience from the Radio Plasma Imaging @PI) experiment on the IMAGE spacecraft in Earth orbit, in support of the subsurface measurement objectives.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Europa's Icy Shell: Past, Present, and Future; 48; LPI-Contrib-1195
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  • 18
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    Cratering Rates in the Jovian System (2004)
    In:  CASI
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    Publication Date: 2004-10-05
    Description: We use several independent constraints on the number of ecliptic comets to estimate impact cratering rates on the Jupiter moons. The impact rate on Jupiter by 1.5-km diameter ecliptic comets is currently NY(d 〉 1.5km) = 0.005(+0.006)(-0.003) per annum. Asteroids and long period comets are currently unimportant. The size-number distribution of ecliptic comets smaller than 20 km is inferred from size-number distributions of impact craters on Europa, Ganymede, and Triton. For comets bigger than 50 km we use the size-number distribution of Kuiper Belt Objects. The overview of the impact rate at Jupiter in general and at Europa in particular are given. These impact rates imply cratering rates on Europa of 0.5 per Ma per 10(exp 6) sq km for impact craters bigger than 1 km, and of 0.015 per Ma per 10(exp 6) sq km for impact craters bigger than 20 km. The latter corresponds to an average recurrence time of 2.2 Ma for 20 km craters. The best current estimates for the number of 20 km craters on Europa appear to range between about twelve to thirty. This implies that the average age of Europa's surface is between 30 and 70 Ma. The average density of craters with diameter greater than 1 km on well-mapped swaths on Europa is 30 per 10(exp 6) sq km. The corresponding nominal surface age would be 60 Ma. These two estimates are not truly independent because we have used size-number distribution of the Europan craters to help generate the size-number distribution of comets. The uncertainty of the best estimate - call it 42 Ma for specificity - is at least a factor of 3.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Europa's Icy Shell: Past, Present, and Future; 98-99; LPI-Contrib-1195
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  • 19
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    Heavy ion observations by MARIE in cruise phase and Mars orbit (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The charged particle spectrum for nuclei from protons to neon, (charge Z=10) was observed during the cruise phase and orbit around Mars by the MARIE charged particle spectrometer on the Odyssey spacecraft. The cruise data were taken between April 23, 2001 and mid-August 2001. The Mars orbit data were taken March 5, 2002 through May 2002 and are scheduled to continue until August 2004. Charge peaks are clearly separated for charges up to Z=10. Especially prominent are the carbon and oxygen peaks, with boron and nitrogen also clearly visible. Although heavy ions are much less abundant than protons in the cosmic ray environment, it is important to determine their abundances because their ionization energy losses (proportional to Z2) are far more dangerous to humans and to instruments. Thus the higher charged nuclei make a significant contribution to dose and dose equivalent received in space. Results of the charged particle spectrum measurements will be reported. c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Advances in space research : the official journal of the Committee on Space Research (COSPAR); Volume 33; 12; 2211-4
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  • 20
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    Modeling the nucleus and jets of comet 81P/Wild 2 based on the Stardust encounter data (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We interpret the nucleus properties and jet activity from the Stardust spacecraft imaging and the onboard dust monitoring system data. Triangulation of 20 jets shows that 2 emanate from the nucleus dark side and 16 emanate from sources that are on slopes where the Sun's elevation is greater than predicted from the fitted triaxial ellipsoid. Seven sources, including five in the Mayo depression, coincide with relatively bright surface spots. Fitting the imaged jets, the spikelike temporal distribution of dust impacts indicates that the spacecraft crossed thin, densely populated sheets of particulate ejecta extending from small sources on the rotating nucleus, consistent with an emission cone model.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 304; 5678; 1769-74
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  • 21
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    Recovery and Utilization of Extraterrestrial Resources (2004)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: This special bibliography includes the extraction, processing, and utilization of lunar, planetary, and asteroid resources; mining and excavation equipment, oxygen and propellant production; and in situ resource utilization.
    Keywords: Lunar and Planetary Science and Exploration
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  • 22
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    Bangui Anomaly (2004)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Bangui anomaly is the name given to one of the Earth s largest crustal magnetic anomalies and the largest over the African continent. It covers two-thirds of the Central African Republic and therefore the name derives from the capitol city-Bangui that is also near the center of this feature. From surface magnetic survey data Godivier and Le Donche (1962) were the first to describe this anomaly. Subsequently high-altitude world magnetic surveying by the U.S. Naval Oceanographic Office (Project Magnet) recorded a greater than 1000 nT dipolar, peak-to-trough anomaly with the major portion being negative (figure 1). Satellite observations (Cosmos 49) were first reported in 1964, these revealed a 40nT anomaly at 350 km altitude. Subsequently the higher altitude (417-499km) POGO (Polar Orbiting Geomagnetic Observatory) satellite data recorded peak-to-trough anomalies of 20 nT these data were added to Cosmos 49 measurements by Regan et al. (1975) for a regional satellite altitude map. In October 1979, with the launch of Magsat, a satellite designed to measure crustal magnetic anomalies, a more uniform satellite altitude magnetic map was obtained. These data, computed at 375 km altitude recorded a -22 nT anomaly (figure 2). This elliptically shaped anomaly is approximately 760 by 1000 km and is centered at 6%, 18%. The Bangui anomaly is composed of three segments; there are two positive anomalies lobes north and south of a large central negative field. This displays the classic pattern of a magnetic anomalous body being magnetized by induction in a zero inclination field. This is not surprising since the magnetic equator passes near the center of this body.
    Keywords: Geophysics
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  • 23
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    Planetary In Situ Resource Utilization: 2000-2004 (2004)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: This custom bibliography from the NASA Scientific and Technical Information Program lists a sampling of records found in the NASA Aeronautics and Space Database. The scope of this topic includes technologies for ultimately enabling us to "cut the cord" with Earth for space logistics. This area of focus is one of the enabling technologies as defined by NASA s Report of the President s Commission on Implementation of United States Space Exploration Policy, published in June 2004.
    Keywords: Lunar and Planetary Science and Exploration
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  • 24
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    Simulation of Helium-3 Extraction from Lunar Ilmenite (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Knowledge of the trapping mechanisms and diffusion characteristics of solar-wind implanted isotopes in the minerals of the lunar regolith will enable the optimization of the processes to extract solar wind gases from regolith particles. Extraction parameters include the temperature and duration of extraction, particle size, and gas yield. Diffusion data will increase the efficiency and profitability of future mining ventures. This data will also assist in optimizing the evaluations of various potential mining sites based on remote sensing data. For instance, if magnesian ilmenite (Mg,Fel.,Ti03) is found to retain He better than stoichiometric ilmenite (FeTi03), remote sensing data for Mg could be considered in addition to Ti and maturity data. The context of the currently discussed work is the mining of helium-3 for potential use as a fuel for fusion energy generation. However, the potential resources deposited by the solar wind include hydrogen (and derived water), helium-4, nitrogen and carbon. Implantation experiments such as those performed for helium isotopes in ilmenite are important for the optimized extraction of these additional resources. These experiments can easily be reproduced for most elements or isotopes of interest.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Space Resources Roundtable VI; 28; LPI-Contrib-1224
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    A Magnetic Perspective on the Martian Crustal Dichotomy (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Mars Global Surveyor spacecraft has completed two Mars years in nearly circular polar orbit at a nominal altitude of 400 km. The Mars crust is at least an order of magnitude more intensely magnetized than that of the Earth, and intriguing in both its global distribution and geometric properties. Measurements of the vector magnetic field have been used to map the magnetic field of crustal origin to high accuracy. This most recent map is assembled from 〉 2 full years of MGS night-side observations, and uses along-track filtering to greatly reduce noise due to external field variations. Additional information is included in the original extended abstract.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 11-12; LPI-Contrib-1213
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  • 26
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    Subsurface Structure of the Ismenius Area and Implications for Evolution of the Martian Dichotomy and Magnetic Field (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Martian dichotomy divides the smooth, northern lowlands from the rougher southern highlands. The northern lowlands are largely free of magnetic anomalies, while the majority of the significant magnetic anomalies are located in the southern highlands. An elevation change of 2-4 km is typical across the dichotomy, and is up to 6 km locally. We examine a part of the dichotomy that is likely to preserve the early history of the dichotomy as it is relatively unaffected by major impacts and erosion. This study contains three parts: 1) the geologic history, which is summarized below and detailed in McGill et al., 2) the study of the gravity and magnetic field to better constrain the subsurface structure and history of the magnetic field (this abstract), and 3) modeling of the relaxation of this area. Our overall goal is to place constraints on formation models of the dichotomy by constraining lithospheric properties. Initial results for the analysis of the geology, gravity, and magnetic field studies are synthesized in Smrekar et al..
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 60-61; LPI-Contrib-1213
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  • 27
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    Ancient Giant Basin/Aquifer System in the Arabia Region, Mars, and Its Influence on the Evolution of the Highland-Lowland Boundary (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Ancient geologic and hydrologic phenomena on Mars observed through the magnetic data provide windows to the ancient past through the younger Argyre and Hellas impacts, the northern plains basement and the rock materials that mantle the basement, and the Tharsis and Elysium magmatic complexes (recently referred to as superplumes). These signatures, coupled with highly degraded macrostructures (tectonic features that energetic planet during its embryonic development (0.5 Ga or so of activity) with an active dynamo and magnetosphere. One such window into the ancient past occurs northwest of the Hellas impact basin in Arabia Tern. Arabia Terra is one of the few water-rich equatorial regions of Mars, as indicated I through impact crater and elemental information. This region records many unique characteristics, including predominately Noachian materials, a highland-lowland boundary region that is distinct from other boundary regions, the presence of very few macrostructures when compared to the rest of the cratered highlands, the largest region of fretted terrain on Mars, outflow channels such as Mamers Valles that do not have obvious origins, and distinct albedo, thermal inertia, gravity, magnetic, and elemental signatures.
    Keywords: Geophysics
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 13-14; LPI-Contrib-1213
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  • 28
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    Topographic Change of the Dichotomy Boundary Suggested by Crustal Inversion (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Linear negative gravity anomalies in Acidalia Planitia along the eastern edge of Tempe Terra and along the northern edge of Arabia Terra have been noted in Mars Global Surveyor gravity fields. Once proposed to represent buried fluvial channels, it is now believed that these gravity troughs mainly arise from partial compensation of the hemispheric dichotomy topographic scarp. A recent inversion for crustal structure finds that mantle compensation of the scarp is offset from the present-day topographic expression of the dichotomy boundary. The offset suggests that erosion or other forms of mass wasting occurred after lithosphere thickened and no longer accomodated topographic change through viscous relaxation.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 46-47; LPI-Contrib-1213
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  • 29
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    Impact Constraints on the Age and Origin of the Crustal Dichotomy on Mars (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: MOLA data have revealed a large population of "Quasi-Circular Depressions" (QCDs) with little or no visible expression in image data. These likely buried impact basins have important implications for the age of the lowland crust, how that compares with original highland crust, and when and how the crustal dichotomy may have formed. The buried lowlands are of Early Noachian age, likely slightly younger than the buried highlands but older than the exposed (visible) highland surface. A depopulation of large visible basins at diameters 800 to 1300 km suggests some global scale event early in martian history, maybe related to the formation of the lowlands andor the development of Tharsis. A suggested early disappearance of the global magnetic field can be placed within a temporal sequence of formation of the very largest impact basins. The global field appears to have disappeared at about the time the lowlands formed. It seems likely the topographic crustal dichotomy was produced very early in martian history by processes which operated very quickly. This and the preservation of large relic impact basins in the north- em hemisphere, which themselves can account for the lowland topography, suggest that large impacts played the major role in the origin Mars fundamental crustal feature.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 19-20; LPI-Contrib-1213
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  • 30
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    Constraints on Early Mars Evolution and Dichotomy Origin from Relaxation Modeling of Dichotomy Boundary in the Ismenius Region (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Martian dichotomy is a global feature separating the northern and southern hemispheres. The 3.5 - 4 Gyr old feature is manifested by a topographic difference of 2-6 km and crustal thickness difference of approx. 15 - 30 km between the two hemispheres. In the Ismenius region, sections of the boundary are characterized by a single scarp with a slope of approx. 20 deg. - 23 deg. and are believed to be among the most well preserved parts of the dichotomy boundary. The origin of the dichotomy is unknown. Endogenic hypotheses do not predict the steep slopes (scarps) of the dichotomy boundary. Exogenic models for forming the northern lowlands by impact cratering, associate the scarps along the dichotomy boundary with craters' rims, but are not globally consistent with the topography and gravity. In order to better understand the origin of the Martian dichotomy, it is necessary to know if the steep scarps along the boundary represent the original shape of the dichotomy. Smrekar et al. presented evidence showing that the boundary scarp in Ismenius is a fault along which the highland crust was down faulted. We test whether the relaxation process could produce faulting along the dichotomy boundary and examine the crustal and mantle conditions that would allow for faulting to occur within 1 Gyr and preserve the long wavelength topography over another 3 Gyr. We approach the problem by a combination of numerical and semi-analytical modeling. We test different viscosity profiles and crustal thicknesses by comparing our modeled magnitude, location and timing of plastic strain and displacements to detailed geologic observations in the Ismenius region.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 21-22; LPI-Contrib-1213
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  • 31
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    Crustal Evolution of the Protonilus Mensae Area, Mars (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Despite research by numerous geologists and geo- physicists, the age and origin of the martian crustal dichotomy remain uncertain. Models for the origin of this dichotomy involve single or multiple impact, mantle megaplumes, primordial crustal asymmetry, and plate tectonics. Most of these models imply a Noachian age for the dichotomy. A major problem common to all genetic models is the difficulty separating the features resulting from the primary cause for the dichotomy from features due to younger fault- ing, impact cratering, volcanism, deposition, and erosion. highlands (the dichotomy boundary) approximates a small circle that ranges in latitude from about -10 deg. in Elysium Planitia to about +45 deg. north of Arabia Terra. For much of its length the boundary is characterized by relatively steep scarps separating highland plateau to the south from lowland plains to the north, generally with a complex transition zone on the lowland side of these scarps. These scarps are almost certainly due to normal faulting. The type fretted terrain, which defines the boundary in north-central Arabia Terra, also is characterized by scarps but has under- gone a more complex history of faulting and dissection [13]. In some places, notably in the Acidalia Planitia region, the dichotomy boundary is gradational. In the Tharsis region the boundary is obscured by younger volcanics.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 42-43; LPI-Contrib-1213
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  • 32
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    Deflections in Lava Flow Directions Relative to Topography in the Tharsis Region of Mars: Indications of Post-Flow Tectonic Motion (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: High-resolution topographic data from the Mars Orbiter Laser Altimeter (MOLA), and imagery from the Mars Orbiter Camera (MOC) and the Thermal Emission Imaging System (THEMIS) allow for the first accurate assessment of lava flow directions relative to topographic slopes in the Tharsis region. Tharisis has long been recognized as the dominant tectonic and volcanic province on the planet, with a complex geologic history. In this study, lava flow directions on Daedalia Planum, Syria Planum, Tempe Terra, and near the Tharsis Montes are compared with MOLA topographic contours to look for deviations of flow directions from the local slope direction. The topographic deviations identified in this study are likely due to Tharsis tectonic deformation that has modified the regional topography subsequent to the emplacement of the flows, and can be used to model the mechanisms and magnitudes of relatively recent tectonism in the region. A similar approach was used to identify possible post-flow tectonic subsidence on the Snake River Plain in Idaho.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 33
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    Freshwater Microbialites of Pavilion Lake, British Columbia, Canada: A Limnological Investigation (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Pavillion Lake is 5.7km long and an average of 0.8 km in width, and is located in Marble Canyon in the interior of British Columbia, Canada. It is a slightly alkaline, freshwater lake with a maximum-recorded depth of 65m. The basin walls of Pavilion Lake are lined with microbialite structures that are oriented perpendicularly to the shoreline, and which are found from depths of 5 meters to the bottom of the photic zone (light levels 1% of ambient; approximately 30m depth). These structures are speculated to have begun formation nearly 11,000 years ago, after the glacial retreat of the Cordilleran Ice Sheet. They are likely a distinctive assemblage of freshwater calcite microbialites, which display micromorphologies possibly related to the ancient Epiphyton and Girvanella classes of calcareous organosedimentary structures.
    Keywords: Geophysics
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 34
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    Tumbleweed: Wind-propelled Surficial Measurements for Astrobiology and Planetary Science (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Tumbleweed is a wind-propelled long-range vehicle based on well-developed and tested technology, instrumented to perform surveys Mars analog environments for habitability and suitable for a variety of missions on Mars. Tumbleweeds are light-weight and relatively inexpensive, making it very attractive for multiple deployments or piggy-backing on a larger mission. Tumbleweeds with rigid structures are also being developed for similar applications. Modeling and testing have shown that a 6 meter diameter Tumbleweed is capable of climbing 25 hills, traveling over 1 meter diameter boulders, and ranging over a thousand kilometers. Tumbleweeds have a potential payload capability of about 10 kilograms with approximately 10-20 Watts of power. Stopping for science investigations can also be accomplished using partial deflation or other braking mechanisms. Surveys for Astrobiology and other applications of tumbleweeds are shown.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 35
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    Noachian-Hesperian Transition and a Possible Climatic Optimum: Evidence from Landforms (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: A climatic optimum? The often strong contrast between the pristine and degraded Noachian channels and craters might be due to a gradual climatic change superimposed upon an episode of mantling associated with early Hesperian volcanism. On the other hand, one or more episodes of volcanism or large impacts could have induced global warming and produced a relatively short-lived optimum for precipitation and runoff. The rapid cutoff of fluvial activity following the development of the later pristine fluvial features is consistent with this scenario. We discuss the changing style of erosion in the highlands during the Noachian and early Hesperian in a companion abstract to this workshop. Here we review the some of the morphologic evidence for a possible Noachian-Hesperian (N-H) climate optimum.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 36
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    The Effect of Impacts on the Early Martian Climate (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The first images returned by the Mariner 7 spacecraft of the Martian surface showed a landscape heavily scared by impacts. Mariner 9 imaging revealed geomorphic features including valley networks and outflow channels that suggest liquid water once flowed at the surface of Mars. Further evidence for water erosion and surface modification has come from the Viking Spacecraft, Mars Pathfinder, Mars Global Surveyor's (MGS) Mars Orbiter Camera (MOC), and Mars Odyssey's THEMIS instrument. In addition to network channels, this evidence includes apparent paleolake beds, fluvial fans and sedimentary layers. The estimated erosion rates necessary to explain the observed surface morphologies present a conundrum. The rates of erosion appear to be highest when the early sun was fainter and only 75% as luminous as it is today. All of this evidence points to a very different climate than what exists on Mars today. The most popular paradigm for the formation of the valley networks is that Mars had at one time a warm (T average 〉 273), wetter and stable climate. Possible warming mechanisms have included increased surface pressures, carbon dioxide clouds and trace greenhouse gasses. Yet to date climate models have not been able to produce a continuously warm and wet early Mars. The rates of erosion appear to correlate with the rate at which Mars was impacted thus an alternate possibility is transient warm and wet conditions initiated by large impacts. It is widely accepted that even relatively small impacts (approx. 10 km) have altered the past climate of Earth to such an extent as to cause mass extinctions. Mars has been impacted with a similar distribution of objects. The impact record at Mars is preserved in the abundance of observable craters on it surface. Impact induced climate change must have occurred on Mars.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 37
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    A Subsurface Soil Composition and Physical Properties Experiment to Address Mars Regolith Stratigraphy (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Previous in-situ measurements of soil-like materials on the surface of Mars, in particular during the on-going Mars Exploration Rover missions, have shown complex relationships between composition, exposure to the surface environment, texture, and local rocks. In particular, a diversity in both compositional and physical properties could be established that is interpreted to be diagnostic of the complex geologic history of the martian surface layer. Physical and chemical properties vary laterally and vertically, providing insight into the composition of rocks from which soils derive, and environmental conditions that led to soil formation. They are central to understanding whether habitable environments existed on Mars in the distant past. An instrument the Mole for Soil Compositional Studies and Sampling (MOCSS) - is proposed to allow repeated access to subsurface regolith on Mars to depths of up to 1.5 meters for in-situ measurements of elemental composition and of physical and thermophysical properties, as well as for subsurface sample acquisition. MOCSS is based on the compact PLUTO (PLanetary Underground TOol) Mole system developed for the Beagle 2 lander and incorporates a small X-ray fluorescence spectrometer within the Mole which is a new development. Overall MOCSS mass is approximately 1.4 kilograms. Taken together, the MOCSS science data support to decipher the geologic history at the landing site as compositional and textural stratigraphy if they exist - can be detected at a number of places if the MOCSS were accommodated on a rover such as MSL. Based on uncovered stratigraphy, the regional sequence of depositional and erosional styles can be constrained which has an impact on understanding the ancient history of the Martian near-surface layer, considering estimates of Mars soil production rates of 0.5... 1.0 meters per billion years on the one hand and Mole subsurface access capability of approximately 1.5 meters. An overview of the MOCSS, XRS instrument accomodation and the impact that these instruments have on Mars science is discussed.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 38
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    Chemical and Isotopic Study of Lab-formed Carbonates Under Cryogenic and Hydrothermal Conditions (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Aqueous environments on early Mars were probably relatively short-lived and localized, as evidenced by the lack of abundant secondary minerals detected by the TES instrument. In order to better understand the aqueous history of early Mars we need to be able to interpret the evidence preserved in secondary minerals formed during these aqueous events. Carbonate minerals, in particular, are important secondary minerals for interpreting past aqueous environments as illustrated by the carbonates preserved in ALH84001. Carbonates formed in short-lived, dynamic aqueous events often preserve kinetic rather than equilibrium chemical and isotopic processes, and predicting the behavior of such systems is facilitated by empirical data.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 39
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    Validating Ancient Age of the Buried Floor of the Northern Lowlands, Mars (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Hesperian and Amazonian plains units cover the northern lowlands but little is known about what this surface covers. Models for the creation of the lowlands and the dichotomy boundary implement mechanisms which vary from internal processes, such as plate tectonics or first-order mantle convection, to external processes, such as a single large impact or multiple impacts. Different models require different time scales for low-land formation; determining the age of the buried low-land surface would help constrain the formation models. The Mars Orbiting Laser Altimeter (MOLA) has yielded a high-precision, topographic gridded data set that reveals the presence of Quasi-Circular Depressions (QCDs) in both the southern highlands and the northern lowlands. Most of these roughly circular depressions have no corresponding visible structural feature on the surface. It is proposed that these QCDs are the surface representation of buried impact craters. Based on this assumption, cumulative number vs. diameter curves were constructed, which placed the age of the buried surface of the northern lowlands in the Early or pre-Noachian. A Noachian basement is supported by the remnants of large craters and multi-ring basins discovered in earlier research, but the QCDs provide the first evidence of this for the entire lowland. Constraining the age of the basement floor to the earliest Noachian, however, would require that the process that formed the northern lowlands either occurred in the early Noachian or involves removal of material from the bottom of the crust without destroying the previously formed craters to achieve the modeled crustal thinning. But can we establish that the QCDs do in fact represent buried impact craters, and thus validate an Early Noachian age for the buried lowland floor?
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 40
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    Impact Constraints on Major Events in Early Mars History (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: MOLA data have revealed a large population of "Quasi-Circular Depressions" (QCDs) with little or no visible expression in image data. These likely buried impact basins have important implications for the age of the lowland crust, how that compares with original highland crust, and when and how the crustal dichotomy may have formed. The buried lowlands are of Early Noachian age, likely slightly younger than the buried highlands but older than the exposed (visible) highland surface. A depopulation of large visible basins at diameters 800 to 1300 km suggests some global scale event early in martian history, maybe related to the formation of the lowlands and/or the development of Tharsis. A suggested early disappearance of the global magnetic field can be placed within a temporal sequence of formation of the very largest impact basins. The global field appears to have disappeared at about the time the lowlands formed. It seems likely the topographic crustal dichotomy was produced very early in martian history by processes which operated very quickly. Thus there appears to have been a northern lowland throughout nearly all of martian history, predating the last of the really large impacts (Hellas, Argyre and Isidis) and their likely very significant environmental consequences.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 41
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    Updating the Evidence for Oceans on Early Mars (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Different-sized bodies of water have been proposed to have occurred episodically in the lowlands of Mars throughout the planet's history, largely related to major stages of development of Tharsis and/or orbital obliquity. These water bodies range from large oceans in the Noachian-Early Hesperian, to a minor sea in the Late Hesperian, and dispersed lakes during the Amazonian. To evaluate the more recent discoveries regarding the oceanic possibility, here we perform a comprehensive analysis of the evolution of water on Mars, including: 1. Geological assessment of proposed shorelines; 2. A volumetric approximation to the plains-filing proposed oceans; 3. Geochemistry of the oceans and derived mineralogies; 4. Post-oceanic (i.e., Amazonian) evolution of the shorelines; and 5. Ultimate water evolution on Mars.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 42
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    Geologic Evolution of Eastern Hellas, Mars: Styles and Timing of Volatile-driven Activity (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The east rim of the Hellas basin and the surrounding highlands comprise a geologically significant region for evaluating volatile abundance, volatile distribution and cycling, and potential changes in Martian environmental conditions. This region of the Martian surface exhibits landforms shaped by a diversity of geologic processes and has a well-preserved geologic record, with exposures of Noachian, Hesperian, and Amazonian units, as well as spans a wide range in both latitude and elevation due to the magnitude of Hellas basin. In addition, geologically contemporaneous volcanism and volatile-driven activity in the circum-Hellas highlands provide important ingredients for creating habitats for potential Martian life.
    Keywords: Geophysics
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 43
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    New Perspectives on Ancient Mars (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Global data sets returned by the Mars Global Surveyor (MGS), Mars Odyssey, and Mars Express spacecraft and recent analyses of Martian meteorites suggest that most of the major geological events of Martian history occurred within the first billion years of solar system formation. This period was a time of heavy impact bombardment of the inner solar system, a process that strongly overprinted much of the Martian geological record from that time. Geophysical signatures nonetheless remain from that period in the Martian crust, and several geochemical tracers of early events are found in Martian meteorites. Collectively, these observations provide insight into the earliest era in Martian history when the conditions favoring life were best satisfied.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Second Conference on Early Mars: Geologic, Hydrologic, and Climatic Evolution and the Implications for Life; LPI-Contrib-1211
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  • 44
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    Mars Science Laboratory: entry, descent and landing system overview (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Keywords: Lunar and Planetary Science and Exploration
    Type: 2004 IEEE Aerospace Conference; Big Sky, MT; United States
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  • 45
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    Asteroid 5535 Annefrank size, shape, and orientation: Stardust first results (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: The NASA Discovery Stardust spacecraft flew by the main belt asteroid 5535 Annefrank at a distance of 3100 km and a speed of 7.4 km/s in November 2002 to test the encounter sequence developed for its primary science target, the comet 81P/Wild2. During this testing, over 70 images of Annefrank were obtained, taken over a phase angle range from 40 to 140 degrees.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Journal of Geophysical Research; Volume 109
    Format: text
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    A study of ozone variability and its connection with meridional transport in the northern Pacific lower stratosphere during summer 2002 (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: A preliminary study of the impact of the north-central Pacific circulation in the subtropical stratosphere on ozone variability locally observed by lidar is presented.
    Keywords: Geophysics
    Type: Journal of Geophysical Research; Volume 109; D11105-11118
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    Volcanic Activity at Tvashtar Catena, Io (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Tvashtar Catena (63 N, 120 W) is one of the most interesting features on Io. This chain of large paterae (caldera-like depressions) has exhibited highly variable volcanic activity in a series of observations. Tvashtar is the type example of a style of volcanism seen only at high latitudes, with short-lived Pele-type plumes and short-lived by intense thermal events. Evidence for a hot spot at Tvashtar was first detected in an eclipse observation in April 1997 (orbit G7) by the Solid State Imager (SSI) on the Galileo Spacecraft. Tvashtar was originally targeted for observation at higher resolution in the close flyby in November 1999 (I25) because of its interesting large-scale topography. There are relatively few but generally larger paterae at high latitudes on Io. I25 images revealed a 25 km long, 1-2 km high lava curtain via a pattern of saturation and bleeding in the CCD image, which requires very high temperatures.
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXV: Io, with a Dash of Titan; LPI-Contrib-1197
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    Global Distribution of Active Volcanism on Io as Known at the End of the Galileo Mission (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Hot spots are manifestations of Io s mechanism of internal heating and heat transfer. Therefore, the global distribution of hot spots and their power output has important implications for how Io is losing heat. The end of the Galileo mission is an opportune time to revisit studies of the distribution of hot spots on Io, and to investigate the distribution of their power output.
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXV: Io, with a Dash of Titan; LPI-Contrib-1197
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    Lava Lakes on Io: New Perspectives from Modeling (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Ionian paterae are a class of volcanic feature that are characterized by irregular craters with steep walls, flat floors, and arcuate margins that may or may not exhibit nesting. Loki (310 W, 12 N) is Io's largest patera at approx.200 km in diameter (Figure 1), and may account for 15% of Io's total heat flow. Earth-based infrared data, as well as information collected using the Galileo Near-Infrared Mapping Spectrometer (NIMS) and the Photopolarimeter Radiometer (PPR) have been used to interpret Loki s eruption style. Debate continues over whether Loki s occasional (periodic or not) temperature increases are due to an overturning lava lake within the patera, or to an eruption of surface flows on the patera floor. Interpretation of model results and comparisons with active terrestrial lava lakes suggest that Loki behaves quite differently from active lava lakes on Earth, and that surface flows (rather than an overturning lava lake) are a more likely explanation of Loki's thermal brightening.
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXV: Io, with a Dash of Titan; LPI-Contrib-1197
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    How Does Titan Retain a Finite Orbital Eccentricity? (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: There is appreciable evidence for a significant hydrocarbon ocean on the surface of Titan. However, it has long been appreciated that tidal dissipation within a putative hydrocarbon ocean on Titan easily yields an orbital eccentricity damping time e which is short compared to the age of the solar system. Unless Titan s present eccentricity (e = 0.0288) were acquired recently, it requires that either: the ocean has a configuration which limits dissipation, or some mechanism exists which effectively maintains the eccentricity against dissipative damping. We argue for the latter. Specifically, the proximity of Jupiter and Saturn to a 5:2 mean motion resonance may provide a sufficient excitation source, and thereby effectively remove dynamical constraints on the dissipation and configuration of the Titan ocean.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Io, with a Dash of Titan; LPI-Contrib-1197
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    Relationships Between Paterae, Mountains, and Hotspots on Io from a Global Database (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Now that the Galileo spacecraft s tour of the Jupiter system is over, we seek to integrate all available datasets in the hopes of understanding Io as completely as possible. We have compiled information about the morphologies and locations of paterae (volcano-tectonic depressions), mountains, and hotspots on Io in a single database. It is our hope that an analysis of the spatial and temporal relationships between these features will provide more indications of the nature of the crust of Io and the mechanisms leading to these features formation. Since Io s tidal heat escapes through its crust, more knowledge about the crust will lead to an understanding of internal processes, such as magma generation and delivery to the surface, and magnitude and orientation of internal stresses.
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXV: Io, with a Dash of Titan; LPI-Contrib-1197
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    Preparing for Themis Controlled Global Mars Mosaics (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: We have begun work to prepare for producing controlled 2001 Mars Odyssey THEMIS infrared (IR) and visible (VIS) global mosaics of Mars. This effort is being coordinated with colleagues from Arizona State University and on the THEMIS team who plan to address radiometric issues in making such mosaics. We are concentrating on geometric issues. Several areas of investigation are now in progress, including: a) characterizing the absolute pointing accuracy of THEMIS images; b) investigating whether automatic tie point matching algorithms could be used to provide connections between overlapping THEMIS images; c) developing algorithms to allow for the photogrammetric (bundle) adjustment of the THEMIS IR (line scanner) camera images. Our primary goal in this pilot study effort will be to make several test control THEMIS mosaics and better determine which methods could be used, which require development, and what level of effort is required, in order to make large regional or global controlled THEMIS mosaics.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars: New Methods and Techniques; LPI-Contrib-1197
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    Mars Exploration Rover Panoramic Camera Multidimensional Analyses and Surface Spectral Variability (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The Mars Exploration Rover (MER) panoramic camera system (Pancam) has provided surface-based multispectral image data with unprecedented spatial and radiometric fidelity. The spectral coverage of the camera system allows for the discrimination of important Fe2+ and Fe3+ bearing minerals expected to occur on the Martian surface . This paper explores the spatially coherent and structurally consistent spectral variability present at both the Spirit and Opportunity landing sites using multidimensional analysis of representative Pancam multispectral scenes.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Preliminary Assessment of Mars Exploration Rover Landing Site Predictions (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Selection of the Mars Exploration Rover (MER) landing sites took place over a three year period in which engineering constraints were identified, 155 possible sites were downselected to the final two, surface environments and safety considerations were developed, and the potential science return at the sites was considered. Landing sites in Gusev crater and Meridiani Planum were selected because they appeared acceptably safe for MER landing and roving and had strong morphologic and mineralogical indicators of liquid water in their past and thus appeared capable of addressing the science objectives of the MER missions, which are to determine the aqueous, climatic, and geologic history of sites on Mars where conditions may have been favorable to the preservation of evidence of possible pre-biotic or biotic processes. Engineering constraints important to the selection included: latitude (10 N-15 S) for maximum solar power; elevation (〈-1.3 km) for sufficient atmosphere to slow the lander; low horizontal winds, shear and turbulence in the last few kilometers to minimize horizontal velocity; low 10-m scale slopes to reduce airbag spinup and bounce; moderate rock abundance to reduce abrasion or stroke-out of the airbags; and a radar-reflective, load-bearing and trafficable surface safe for landing and roving that is not dominated by fine-grained dust. In selecting the MER landing sites these engineering constraints were addressed via comprehensive evaluation of surface and atmospheric characteristics from existing remote sensing data and models as well as targeted orbital information acquired from Mars Global Surveyor and Mars Odyssey. This evaluation resulted in a number of predictions of the surface characteristics of the sites, which are tested in this abstract. Relating remote sensing signatures to surface characteristics at landing sites allows these sites to be used as ground truth for the orbital data, is essential for selecting and validating landing sites for future missions, and is required for correctly interpreting the surfaces and materials globally present on Mars.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    First Results of the Athena Microscopic Imager Investigation (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The Athena science payload on the Mars Exploration Rovers (MER) includes the Microscopic Imager (MI). The MI is a fixed-focus camera mounted on an extendable arm, the Instrument Deployment Device (IDD). The MI acquires images at a spatial resolution of 30 microns/pixel over a broad spectral range (400 - 700 nm). The MI uses the same electronics design as the other MER cameras but its optics yield a field of view of 31 x 31 mm across a 1024 x 1024 pixel CCD image. The MI acquires images using only solar or skylight illumination of the target surface. A contact sensor is used to place the MI slightly closer to the target surface than its best focus distance (about 69 mm), allowing concave surfaces to be imaged in good focus. Coarse focusing (approx. 2 mm precision) is achieved by moving the IDD away from a rock target after contact is sensed. The MI optics are protected from the Martian environment by a retractable dust cover. This cover includes a Kapton window that is tinted orange to restrict the spectral bandpass to 500 - 700 nm, allowing crude color information to be obtained by acquiring images with the cover open and closed. The MI science objectives, instrument design and calibration, operation, and data processing were described by Herkenhoff et al. Initial results of the MI experiment on both MER rovers ('Spirit' and 'Opportunity') are described below.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Soil and Rock Physical Properties at the Mars Exploration Rover Landing Sites: Early Returns (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The purpose of this paper is to report the 'early returns' on the physical properties of soil units and rocks at the MER landing sites. Because we are still very early in the mission at Meridiani Planum, results from the Gusev Crater Landing Site are emphasized here.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Transient Liquid Water as a Mechanism for Induration of Soil Crusts on Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The Viking and the Mars Exploration Rover missions observed that the surface of Mars is encrusted by a thinly cemented layer tagged as "duricrust". A hypothesis to explain the formation of duricrust on Mars should address not only the potential mechanisms by which these materials become cemented, but also the textural and compositional components of cemented Martian soils. Elemental analyzes at five sites on Mars show that these soils have sulfur content of up to 4%, and chlorine content of up to 1%. This is consistent with the presence of sulfates and halides as mineral cements. . For comparison, the rock "Adirondack" at the MER site, after the exterior layer was removed, had nearly five times lower sulfur and chlorine content , and the Martian meteorites have ten times lower sulfur and chlorine content, showing that the soil is highly enriched in the saltforming elements compared with rock.Here we propose two alternative models to account for the origin of these crusts, each requiring the action of transient liquid water films to mediate adhesion and cementation of grains. Two alternative versions of the transient water hypothesis are offered, a top down hypothesis that emphasizes the surface deposition of frost, melting and downward migration of liquid water and a bottom up alternative that proposes the presence of interstitial ice/brine, with the upward capillary migration of liquid water.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Localization, Localization, Localization (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Localization of the two Mars Exploration Rovers involved three independent approaches to place the landers with respect to the surface of Mars and to refine the location of those points on the surface with the Mars control net: 1) Track the spacecraft through entry, descent, and landing, then refine the final roll stop position by radio tracking and comparison to images taken during descent; 2) Locate features on the horizon imaged by the two rovers and compare them to the MOC and THEMIS VIS images, and the DIMES images on the two MER landers; and 3) 'Check' and refine locations by acquisition of MOC 1.5 meter and 50 cm/pixel images.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    MER Field Geologic Traverse in Gusev Crater, Mars: Initial Results From the Perspective of Spirit (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: This report casts the initial results of the traverse and science investigations by the Mars Exploration Rover (MER) Spirit at Gusev crater [1] in terms of data sets commonly used in field geologic investigations: Local mapping of geologic features, analyses of selected samples, and their location within the local map, and the regional context of the field traverse in terms of the larger geologic and physiographic region. These elements of the field method are represented in the MER characterization of the Gusev traverse by perspective-based geologic/morphologic maps, the placement of the results from Mossbauer, APXS, Microscopic Imager, Mini-TES and Pancam multispectral studies in context within this geologic/ morphologic map, and the placement of the overall traverse in the context of narrow-angle MOC (Mars Orbiter Camera) and descent images. A major campaign over a significance fraction of the mission will be the first robotic traverse of the ejecta from a Martian impact crater along an approximate radial from the crater center. The Mars Exploration Rovers have been conceptually described as 'robotic field geologists', that is, a suite of instruments with mobility that enables far-field traverses to multiple sites located within a regional map/image base at which in situ analyses may be done. Initial results from MER, where the field geologic method has been used throughout the initial course of the investigation, confirm that this field geologic model is applicable for remote planetary surface exploration. The field geologic method makes use of near-field geologic characteristics ('outcrops') to develop an understanding of the larger geologic context through continuous loop of rational steps focused on real-time hypothesis identification and testing. This poster equates 'outcrops' with the locations of in situ investigations and 'regional context' with the geology over distance of several kilometers. Using this fundamental field geologic method, we have identified the basic local geologic materials on the floor of Gusev at this site, their compositions and likely lithologies, origins, processes that have modified these materials, and their potential significance in the interpretation of the regional geology both spatially and temporally.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Moessbauer Spectroscopy of Soils and Rocks at Gusev Crater and Meridiani Planum (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: For the first time in history a Moessbauer spectrometer was placed on the surface of another planet. The miniaturized Moessbauer spectrometer MIMOS II is part of the Athena payload of NASA's twin Mars Exploration Rovers (MER) Spirit,and Opportunity. It determines the Fe-bearing mineralogy of Martian soils and rocks at the Rovers respective landing sites, Gusev crater and Meridiani Planum. First results of soil and rock measurements at both landing sites confirm a generally basaltic composition of Martian surface materials.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    APXS on Mars: Analyses of Soils and Rocks at Gusev Crater and Meridiani Planum (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Newly developed APXS (Alpha Particle X-Ray Spectrometers) are part of the Athena payload of the Mars Exploration Rovers Spirit and Opportunity [1]. The APXS determines the chemical composition of soils and rocks along the traverse of the two rovers. Spirit and Opportunity operate at Gusev Crater and Meridiani Planum, respectively. First results of soil X-ray spectra at both landing sites support the hypothesis of a global homogenization of the soil by large dust storms and impact processes in the northern and southern hemisphere.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Spirit at Gusev Crater: Preliminary Observations, Potential Processes and Hypotheses (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Spirit landed in a flat plain in Gusev crater with local undulations at meters scales generated by ridges covered with blocks, some of them looking rounded. Several, flat-topped, mesas are visible in the far field in direction of Ma adim Vallis. A set of north/south oriented hills reaches approximately 150 m elevation to the east of the landing site (LS). A dipping brighter unit with possibly some scarps is associated with it. This setting could be consistent with layering observed on the MOC images of the hills, local exposure of material with variable dust cover, or deflated or allochtonous material. Numerous small depressions are visible from LS referred to as "Columbia Memorial Station"* (CMS). Floors are partially filled with finer-grained, high albedo material. At least one of them, nicknamed "Sleepy Hollow"* (approximately 30 m diameter) may be an eroded secondary impact crater. It is unclear if they can all be related to small impact structures. Some of them are elongated and aligned with the ridges. The morphology of rocks and soil at this Gusev Crater is presented. Evidence of dynamic aeolian action along this Crater is also discussed.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Missions; LPI-Contrib-1197
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    Accretion and Heating of Particles by Supersonic Planetesimals (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Recently, nebular shock waves have become one of the leading candidates for explaining the presence of chondrules in primitive meteorites. While shocks have been shown to be capable of explaining many of the features of chondrules, a major problem with the theory is that the source of the shocks remains unidentified. Among the suggested sources of the shocks are bow shocks created by supersonic planetesimals in the nebula. Recently, we studied the structure of the shocks that would form around such supersonic planetesimals. We found that particles that encountered the shocks at distances greater than 2 planetesimal radii from the planetesimal would cool too quickly to form the textures observed in chondrules. While the region of the shock far away from the planetesimal may not allow chondrules to form, the region closer in has not been studied in detail. In this work we consider the dynamical and thermal evolution of particles that encounter supersonic planetesimals in this region.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Origin of Planetary Systems; LPI-Contrib-1197
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    Deflections in Lava Flow Directions Relative to Topography in the Tharsis Region: Indicators of Post-Flow Tectonic Motion (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: High-resolution topographic data for Mars from the Mars Orbiter Laser Altimeter (MOLA), and imagery from the Mars Orbiter Camera (MOC) and the Thermal Emission Imaging System (THEMIS) allow for the first accurate assessment of lava flow directions relative to topographic slopes in the Tharsis region. Tharisis has long been recognized as the dominant tectonic and volcanic province on the planet, with a complex geologic history. In this study, lava flow directions on Daedalia Planum, Syria Planum, Tempe Terra, and near the Tharsis Montes are compared with MOLA topographic contours to look for deviations of flow directions from the local slope direction. The topographic deviations identified in this study are likely due to Tharsis tectonic deformation that has modified the regional topography subsequent to the emplacement of the flows, and can be used to model the mechanisms and magnitudes of relatively recent tectonism in the region. A similar approach was used to identify possible postflow tectonic subsidence on the Snake River Plain in Idaho.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Volcanology and Tectonics; LPI-Contrib-1197
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    Field and Geochemical Study of Table Legs Butte and Quaking Aspen Butte, Eastern Snake River Plain, Idaho: An Analog to the Morphology of Small Shield Volcanoes on Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Mars Orbiter Laser Altimeter (MOLA) data allows insight to Martian features in great detail, revealing numerous small shields in the Tempe region, consisting of low profiles and a prominent summit caps . Terrestrial examples of this shield morphology are found on the Eastern Snake River Plain (ESRP), Idaho. This plains-style volcanism [2] allows an analog to Martian volcanism based on topographic manifestations of volcanic processes . Recent studies link the slope and morphology of Martian volcanoes to eruptive process and style . The ESRP, a 400km long, 100km wide depression, is host to hundreds of tholeiitic basalt shields, which have low-profiles built up over short eruptive periods of a few months or years . Many of these smaller scale shields (basal diameters rarely exceed 5km) display morphology similar to the volcanoes in the Tempe region of Mars . Morphological variations within these tholeiitic shields are beautifully illustrated in their profiles.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Volcanology and Tectonics; LPI-Contrib-1197
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    A Model for Variable Levee Formation Rates in an Active Lava Flow (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Channelized lava flows on Mars and the Earth often feature levees and collateral margins that change in volume along the path of the flow. Consistent with field observations of terrestrial flows, this suggests that the rate of levee formation varies with distance and other factors. Previous models have assumed a constant rate of levee growth, specified by a single parameter, lambda. The rate of levee formation for lava flows is a good indicator of the mass eruption rate and rheology of the flow. Insight into levee formation will help us better understand whether or not the effusion rate was constant during an eruption, and once local topography is considered, allows us to look at cooling and/or rheology changes downslope. Here we present a more realistic extension of the levee formation model that treats the rate of levee growth as a function of distance along the flow path. We show how this model can be used with a terrestrial flow and a long lava flow on Mars. The key statement of the new formulation is the rate of transfer from the active component to the levees (or other passive components) through an element dx along the path of the flow. This volumetric transfer equation is presented.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Volcanology and Tectonics; LPI-Contrib-1197
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    Geomorphologic Studies of a Very Long Lava Flow in Tharsis, Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: CEPS has undertaken an extended study of long lava flows on the terrestrial planets, their location, morphology, and potential modes of emplacement. As part of this ongoing investigation, we have concentrated on a single large flow in Tharsis, with noted similarities to several terrestrial analogs. An impressive series of lava flows emerges from the topographic saddle between Ascraeus and Pavonis Mons. The most prominent of these (hereafter referred to as the 'Saddle Flow') has distinct margins that can be traced for over 480 km in the Viking images, although its exact source cannot be identified. A multimodal approach is utilized in the examination of the Saddle Flow, including image interpretation (VIKING and THEMIS, MOLA topographic analysis and flow profiling, downflow behavior statistical analysis, rheologic modeling, and GIS modeling and integration.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Volcanology and Tectonics; LPI-Contrib-1197
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    A New Oxygen Barometer for Solar System Basaltic Glasses Based on Vanadium Valence (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The determination of oxidation conditions for basaltic magmas derived by the melting of planetary mantles is critical to our understanding of the nature and evolution of planetary interiors. Yet, these determinations are compromised in terrestrial and especially extraterrestrial basalts by our analytical and computational methods for estimating oxygen fugacity (fO2). For example, mineralogical barometers (1, 2) can be reduced in effectiveness by subsolidus re-equilibration of mineral assemblages, inversion of mineralogical data to melt characteristics, and deviations of the natural mineral compositions from ideal thermodynamic parameters.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Special Session: Oxygen in the Solar System, II; LPI-Contrib-1197
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    The Edge of Wetness: The Case for Dry Magmatism on Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The issue of whether martian magmas are wet or dry is an important one. The answer to this basic question has profound consequences for how we think about Mars as a planet. Recently, several lines of evidence have been presented that collectively suggest that shergottite parent magmas were once wet. These include: (i) phase equilibria studies that indicate that the Shergotty parent magma required ~2 wt.% water in order to be co-saturated with both pigeonite and augite, (ii) reverse zoning of light lithophile elements (Li and B) in shergottite pyroxenes, suggesting the exsolution and removal of an aqueous fluid, and (iii) measurement of D/H ratios in SNC minerals that are much lower than atmospheric, suggesting that there may be juvenile (primordial) mantle water. Below I will review the evidence for the diametrically opposite case, that shergottite magmas were effectively dry (〈〈 1 wt.% H2O).
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Martian Meteorites: Hot and Steamy; LPI-Contrib-1197
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    Yamato 980459: The Most Primitive Shergottite? (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: The Antarctic Research Center of the Japanese National Institute of Polar Research (NIPR) recently announced the discovery of a new Martian shergottite, Y98(0459). This sample is a member of the subgroup of basaltic shergottites that contain abundant olivine phenocrysts, and are thus olivine- phyric. Y98 may have special significance among the basaltic shergottites because (1) it appears to have been the most magnesian Martian magma yet found, and thus can provide valuable clues to magma petrogenesis on Mars; (2) it contains no late-crystallizing phases, but instead contains approx. 30% interstitial glass, which can provide unambiguous incompatible element patterns of the parent melt; and (3) it carries an LREE-depleted signature similar to QUE 94201, whose isotopic characteristics are the most primitive of all basaltic shergottites.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Martian Meteorites: Hot and Steamy; LPI-Contrib-1197
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    Rb-Sr and Sm-Nd Isotopic Studies of Shergottite Y980459 and a Petrogenetic Link Between Depleted Shergottites and Nakhlites (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Y980459 was found near the Minami-Yamato Nunataks, Antarctica in 1998 and was recently classified as an olivine-bearing shergottite. It petrographically resembles many other olivine-phyric shergottites mostly found in hot deserts, e.g. DaG476/489, SaU005/094, Dohfar 019, NWA 1068/1110, NWA 1195 and EETA 79001 lith.A. However, Y980459 is unique among these meteorites in several respects. It is apparently very fresh and only weakly shocked. Also, it completely lacks plagioclase, but contains abundant residual volcanic glass. This group of olivine-phyric shergottites is characterized by variable crystallization ages from approx.172 Ma to approx.575 Ma and ejection ages from approx.1 Ma to approx.20 Ma. They probably represent volcanic melts originated from the deep Martian mantle. We performed Rb-Sr and Sm-Nd isotopic analyses on Y980459 to determine its crystallization age and compared its age and isotopic signatures with those obtained from other olivine-phyric shergottites and QUE 94201, the other Antarctic olivine-free shergottite. QUE 94201 and some olivine-phyric shergottites e.g. DaG, SaU, Doh and EETA lith A have similar depleted-LREE patterns and are herein referred to as depleted shergottites. A petrogenetic model correlating depleted shergottites and nakhlites is also proposed. Preliminary Rb-Sr and Sm-Nd isotopic data for Y980459 were presented earlier at the NIPR, Japan, in 2003.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Martian Meteorites: Hot and Steamy; LPI-Contrib-1197
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    Yamato 980459: Crystallization of Martian Magnesian Magma (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Recently, several basaltic shergottites have been found that include magnesian olivines as a major minerals. These have been called olivinephyric shergottites. Yamato 980459, which is a new martian meteorite recovered from the Antarctica by the Japanese Antarctic expedition, is one of them. This meteorite is different from other olivine-phyric shergottites in several key features and will give us important clues to understand crystallization of martian meteorites and the evolution of Martian magma.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Martian Meteorites: Hot and Steamy; LPI-Contrib-1197
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    Cryogenic Calcite: A Morphologic and Isotopic Analog to the ALH84001 Carbonates (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: Martian meteorite ALH84001 carbonates preserve large and variable microscale isotopic compositions, which in some way reflect their formation environment. These measurements show large variations (〉20%) in the carbon and oxygen isotopic compositions of the carbonates on a 10-20 micron scale that are correlated with chemical composition. However, the utilization of these data sets for interpreting the formation conditions of the carbonates is complex due to lack of suitable terrestrial analogs and the difficulty of modeling under non-equilibrium conditions. Thus, the mechanisms and processes are largely unknown that create and preserve large microscale isotopic variations in carbonate minerals. Experimental tests of the possible environments and mechanisms that lead to large microscale isotopic variations can help address these concerns. One possible mechanism for creating large carbon isotopic variations in carbonates involves the freezing of water. Carbonates precipitate during extensive CO2 degassing that occurs during the freezing process as the fluid s decreasing volume drives CO2 out. This rapid CO2 degassing results in a kinetic isotopic fractionation where the CO2 gas has a much lighter isotopic composition causing an enrichment of 13C in the remaining dissolved bicarbonate. This study seeks to determine the suitability of cryogenically formed carbonates as analogs to ALH84001 carbonates. Specifically, our objective is to determine how accurately models using equilibrium fractionation factors approximate the isotopic compositions of cryogenically precipitated carbonates. This includes determining the accuracy of applying equilibrium fractionation factors during a kinetic process, and determining how isotopic variations in the fluid are preserved in microscale variations in the precipitated carbonates.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Martian Meteorites: Hot and Steamy; LPI-Contrib-1197
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    Determining Possible Building Blocks of the Earth and Mars (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: One of the fundamental questions concerning planetary formation is exactly what material did the planets form from? All the planets in our solar system are believed to have formed out of material from the solar nebula. Chondritic meteorites appear to sample this primitive material. Chondritic meteorites are generally classified into 13 major groups, which have a variety of compositions. Detailed studies of possible building blocks of the terrestrial planets require samples that can be used to estimate the bulk chemistry of these bodies. This study will focus on trying to determine possible building blocks of Earth and Mars since samples of these two planets can be studied in detail in the laboratory.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Oxygen in the Solar System; LPI-Contrib-1197
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    Oxygen Fugacity of the Martian Mantle from Pigeonite/Melt Partitioning of Samarium, Europium and Gadolinium (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: This study is part of an ongoing effort to calibrate the pyroxene/melt REE oxybarometer for conditions relevant to the martian meteorites. These efforts have been motivated by reports of redox variations among the shergottites . We have conducted experiments on martian composition pigeonite/melt rare earth element partitioning as a function of fO2.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Oxygen in the Solar System; LPI-Contrib-1197
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    An Admittance Survey of Large Volcanoes on Venus: Implications for Volcano Growth (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: Estimates of the thickness of the venusian crust and elastic lithosphere are important in determining the rheological and thermal properties of Venus. These estimates offer insights into what conditions are needed for certain features, such as large volcanoes and coronae, to form. Lithospheric properties for much of the large volcano population on Venus are not well known. Previous studies of elastic thickness (Te) have concentrated on individual or small groups of edifices, or have used volcano models and fixed values of Te to match with observations of volcano morphologies. In addition, previous studies use different methods to estimate lithospheric parameters meaning it is difficult to compare their results. Following recent global studies of the admittance signatures exhibited by the venusian corona population, we performed a similar survey into large volcanoes in an effort to determine the range of lithospheric parameters shown by these features. This survey of the entire large volcano population used the same method throughout so that all estimates could be directly compared. By analysing a large number of edifices and comparing our results to observations of their morphology and models of volcano formation, we can help determine the controlling parameters that govern volcano growth on Venus.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Venus; LPI-Contrib-1197
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    Enhancements in lower stratospheric CH3CN observed by the upper atmosphere research Sattellite Microwave Limb Sounder following boreal forest fires (2004)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: On 25 August 1992, the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite observed a significant enhancement in the abundance of lower stratospheric methyl cyanide (CH3CN) at 100??hPa (~16??km altitude) in a small region off the east coast of Florida.
    Keywords: Geophysics
    Type: Journal of Geophysical Research; Volume 109
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    Fram Strait sea ice outflow (2004)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We summarize 24 years (1978??2) of ice export estimates and examine, over a 9-year record, the associated variability in the time-varying upward-looking sonar (ULS) thickness distributions of the Fram Strait.
    Keywords: Geophysics
    Type: Journal of Geophysical Research; Volume 109; c09009-c01029
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    Data assimilation of ground GPG total electron content into a physics-based ionosheric model by use of the Kalman filter (2004)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: A three-dimensional (3-D) Global Assimilative Ionospheric Model (GAIM) is currently being developed by a joint University of Southern California and Jet Propulsion Laboratory (JPL) team. To estimate the electron density on a global grid, GAIM uses a first-principles ionospheric physics model and the Kalman filter as one of its possible estimation techniques.
    Keywords: Geophysics
    Type: Radio science; Volume 39
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    Current State of Modeling the Photochemistry of Titan's Mutually Dependent Atmosphere and Ionosphere (2004)
    In:  Other Sources
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    Publication Date: 2018-06-11
    Description: In the context of recent observations, microphysical models, and laboratory data, a photochemical model of Titan's atmosphere, including updated chemistry focusing on rate coefficients and cross sections measured under appropriate conditions, has been developed to increase understanding of these processes and improve upon previous Titan photochemical models. The model employs a two-stream discrete ordinates method to characterize the transfer of solar radiation, and the effects of electron-impact, cosmic-ray deposition, and aerosol opacities from fractal and Mie particles are analyzed. Sensitivity studies demonstrate that an eddy diffusion profile with a homopause level of 850 km and a methane stratospheric mole fraction of 2.2% provides the best fit of stratospheric and upper atmosphere observations and an improved fit over previous Titan photochemical models. Lack of fits for C3H8, HC3N, and possibly C2H3CN can be resolved with adjustments in aerosol opacity. The model presents a benzene profile consistent with its detection in Titan's stratosphere [Coustenis et al., 2003], which may play an important role in the formation of Titan hazes. An electron peak concentration of 4200 cm(exp -3) is calculated, which exceeds observations by 20%, considerably lower than previous ionosphere models. With adjustments in aerosol opacities and surface fluxes the model illustrates that reasonable fits to existing observations are possible with a single eddy diffusion profile, contrary to the conclusions of previous Titan models. These results will aid in the receipt and interpretation of data from Cassini-Huygens, which will arrive at Titan in 2004 and deploy a probe into Titan's atmosphere in January 2005.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Journal of Geophysical Research; Volume 109
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    Mesoscale Gravity Wave Variances from AMSU-A Radiances (2004)
    In:  Other Sources
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    Publication Date: 2018-06-11
    Description: A variance analysis technique is developed here to extract gravity wave (GW) induced temperature fluctuations from NOAA AMSU-A (Advanced Microwave Sounding Unit-A) radiance measurements. By carefully removing the instrument/measurement noise, the algorithm can produce reliable GW variances with the minimum detectable value as small as 0.1 K2. Preliminary analyses with AMSU-A data show GW variance maps in the stratosphere have very similar distributions to those found with the UARS MLS (Upper Atmosphere Research Satellite Microwave Limb Sounder). However, the AMSU-A offers better horizontal and temporal resolution for observing regional GW variability, such as activity over sub-Antarctic islands.
    Keywords: Geophysics
    Type: Geophysical Research Letters; Volume 31
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    Laboratory Evidence for a Key Intermediate in the Venus Atmosphere: Peroxychloroformyl Radical (2004)
    In:  Other Sources
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    Publication Date: 2018-06-11
    Description: For two decades, the peroxychloroformyl radical, ClC(O)OO, has played a central role in models of the chemical stability of the Venus atmosphere. No confirmation, however, has been possible in the absence of laboratory measurements for ClC(O)OO. We report the isolation of ClC(O)OO in a cryogenic matrix and its infrared and ultraviolet spectral signatures. These experiments show that ClC(O)OO is thermally and photolytically stable in the Venus atmosphere. These experimental discoveries validate the existence of ClC(O)OO, confirm several longstanding model assumptions, and provide a basis for the astronomical search for this important radical species.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Proceedings of The National Academy of Sciences of the United States Of America; Volume 101; No. 39; 14007-14010
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    Global Dayside Ionospheric Uplift and Enhancement Associated with Interplanetary Electric Fields (2004)
    In:  Other Sources
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    Publication Date: 2018-06-11
    Description: The interplanetary shock/electric field event of 5-6 November 2001 is analyzed using ACE interplanetary data. The consequential ionospheric effects are studied using GPS receiver data from the CHAMP and SAC-C satellites and altimeter data from the TOPEX/ Poseidon satellite. Data from ~100 ground-based GPS receivers as well as Brazilian Digisonde and Pacific sector magnetometer data are also used. The dawn-to-dusk interplanetary electric field was initially ~33 mV/m just after the forward shock (IMF BZ = -48 nT) and later reached a peak value of ~54 mV/m 1 hour and 40 min later (BZ = -78 nT). The electric field was ~45 mV/m (BZ = -65 nT) 2 hours after the shock. This electric field generated a magnetic storm of intensity DST = -275 nT. The dayside satellite GPS receiver data plus ground-based GPS data indicate that the entire equatorial and midlatitude (up to +/-50(deg) magnetic latitude (MLAT)) dayside ionosphere was uplifted, significantly increasing the electron content (and densities) at altitudes greater than 430 km (CHAMP orbital altitude). This uplift peaked ~2 1/2 hours after the shock passage. The effect of the uplift on the ionospheric total electron content (TEC) lasted for 4 to 5 hours. Our hypothesis is that the interplanetary electric field ''promptly penetrated'' to the ionosphere, and the dayside plasma was convected (by E x B) to higher altitudes. Plasma upward transport/convergence led to a ~55-60% increase in equatorial ionospheric TEC to values above ~430 km (at 1930 LT). This transport/convergence plus photoionization of atmospheric neutrals at lower altitudes caused a 21% TEC increase in equatorial ionospheric TEC at ~1400 LT (from ground-based measurements). During the intense electric field interval, there was a sharp plasma ''shoulder'' detected at midlatitudes by the GPS receiver and altimeter satellites. This shoulder moves equatorward from -54(deg) to -37(deg) MLAT during the development of the main phase of the magnetic storm. We presume this to be an ionospheric signature of the plasmapause and its motion. The total TEC increase of this shoulder is ~80%. Part of this increase may be due to a "superfountain effect." The dayside ionospheric TEC above ~430 km decreased to values ~45% lower than quiet day values 7 to 9 hours after the beginning of the electric field event. The total equatorial ionospheric TEC decrease was ~16%. This decrease occurred both at midlatitudes and at the equator. We presume that thermospheric winds and neutral composition changes produced by the storm-time Joule heating, disturbance dynamo electric fields, and electric fields at auroral and subauroral latitudes are responsible for these decreases.
    Keywords: Geophysics
    Type: Journal Of Geophysical Research (ISSN 0148-0227); Volume 109
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    Geologic Evolution of the Martian Dichotomy in the Ismenius Area of Mars and Implications for Plains Magnetization (2004)
    In:  Other Sources
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    Publication Date: 2018-06-11
    Description: The origin of the Martian dichotomy, which divides highlands from lowlands, is unknown. We examine a section of the dichotomy ( 50 - 90E) defined by steep scarps and normal faults. Stratigraphy and age relationships preclude the formation of the 2.5 km high boundary via erosion. The abrupt disappearance of topographic knobs similar to 300 - 500 km to the northeast is interpreted as a buried fault. Alignment of the buried fault with grabens, stratigraphy, and age determinations using crater counts indicate that the lowland bench is down faulted highlands crust. The estimated local strain (3.5%) and fault pattern are broadly consistent with gravitational relaxation of a plateau boundary. Magnetic and gravity anomalies occur on either side of the buried fault. Admittance analysis indicates isostatic compensation. Although nonunique, a model with a 10 km thick intracrustal block under the lowland bench, a 20 km thick block under the plains, and an excess density of 200 kg/m(3) provides a good fit to the isostatic anomaly. A good fit to a profile of the magnetic field perpendicular to the dichotomy is produced using uniformly polarized intracrustal blocks 10 - 20 km thick, an intensity of 6 Am/m, a field inclination of -30 degrees, and gaps aligned with the isostatic anomalies. One interpretation is that high-density intrusions demagnetized the crust after dynamo cessation and that low-lying magnetized areas could be down faulted highlands crust. Another model (inclination of 30 degrees) has magnetized crust beneath the isostatic anomalies, separated by gaps. The gaps could result from hydrothermal alteration of the crust along fault zones.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Journal of Geophysical Research; Volume 109
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    Redox Conditions Among the Terrestrial Planets (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: Early solar system conditions should have been extremely reducing. The redox state of the early solar nebula was determined by the H2O/H2 of the gas, which is calculated (based on solar composition) to have been about IW-5. At high temperature under such conditions, ferrous iron would exist only as a trace element in silicates and the most common type of chondritic material should have been enstatite chondrites. The observation that E-chondrites form only a subset of the chondrite suite and that the terrestrial planets (Earth, Moon, Mars, Venus, 4 Vesta) contain ferrous and ferric iron as major and minor elements, respectively, implies that either most chondritic materials formed under conditions that were not solar or that early-formed metals oxidized at low temperature, producing FeO. For example, equilibrated ordinary chondrites (by definition, common chondritic materials), by their phase assemblage of olivine, orthopyroxene and metal, must fall not far from the QFI (Quartz-Fayalite-Iron) oxygen buffer. The QFI buffer is about IW-0.5 and, as we shall see, this fo2 is close to that inferred for many materials in the inner solar system.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Special Session: Oxygen in the Solar System, I; LPI-Contrib-1197
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    Topographic Analysis of Quasi-Circular Depressions Around the Utopia Basin, Mars (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: The Mars Orbiting Laser Altimeter (MOLA) has yielded a high-precision, topographic gridded data set. These data reveal the presence of Quasi-Circular Depressions (QCDs) in both the southern highlands and the northern lowlands . Many of these roughly circular depressions have no corresponding visible structural feature on the surface. It is proposed that these QCDs are the surface representation of buried impact craters . Based on this assumption, cumulative number vs. diameter curves were constructed, which placed the age of the buried surface of the northern lowlands in the Early Noachian .
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Tectonism and Volcanism; LPI-Contrib-1197
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    Cerberus Fossae and Elysium Planitia Lavas, Mars: Source Vents, Flow Rates, Edifice Styles and Water Interactions (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: The Cerberus Fossae and Elysium Planitia regions have been suggested as some of the youngest martian surfaces since the Viking mission, although there was doubt whether the origins were predominantly volcanic or fluvial. The Mars Global Surveyor and Mars Odyssey Missions have shown that the region is certainly young in terms of the topographic preservation and the youthful crater counts (e.g. in the tens to a few hundred million yrs.). Numerous authors have shown that fluvial and volcanic features share common flow paths and vent systems, and that there is evidence for some interaction between the lava flows and underlying volatiles as well as the use by lavas and water of the same vent system. Given the youthful age and possible water-volcanism interaction environment, we'd like constraints on water and volcanic flux rates and interactions. Here, we model ranges of volcanic flow rates where we can well-constrain them, and consider the modest flow rate results results in context with local eruption styles, and track vent locations, edifice volumes, and flow sources and data.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Tectonism and Volcanism; LPI-Contrib-1197
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    Fast, Repeatable Clumping of Solid Particles in Microgravity (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: A crucial step in planet formation is the growth of solid bodies in the sub-millimeter to meter size range: too large to condense directly from the gas phase and too small to interact meaningfully through mutual gravitation. The existence of planets in our solar system demands that some growth process once operated in that size regime, but the mechanism has not been positively identified. Whatever it was, it worked despite nebular turbulence that was probably strong enough to break dust structures cohering by weak surface forces and to disrupt small-scale gravitational collapse via the Goldreich-Ward mechanism. Recent work on this topic, reviewed in, has focussed on ice and frost in the laboratory, silicate dust in drop-tower and orbital microgravity environments, and numerically modelled magnetic particles.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Origin of Planetary Systems; LPI-Contrib-1197
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    On the Final Mass of Giant Planets (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: In the core accretion model of giant planet formation, when the core reaches critical mass, hydrostatic equilibrium is no longer possible and gas accretion ensues. If the envelope is radiative, the critical core mass is nearly independent of the boundary conditions and is roughly M(sub crit) ~ 10Mass of the Earth (with weak dependence on the rate of planetesimal accretion M(sub core) and the disk opacity k). Given that such a core may form at the present location of Jupiter in a time comparable to its Type I migration time (10(exp 5) - 10(exp 6) years) provided that the nebula was significantly enhanced in solids with respect to the MMSN and stall at this location in a weakly turbulent (alpha approximately less than 10(exp -4) disk, it may be appropriate to assume that such objects inevitably form and drive the evolution of late-phase T Tauri star disks. Here we investigate the final masses of giant planets in disks with one or more than one such cores. Although the presence of several planets would lead to Type II migration (due to the effective viscosity resulting from the planetary tidal torques), we ignore this complication for now and simply assume that each core has stalled at its location in the disk. Once a core has achieved critical mass, its gaseous accretion is governed by the given Kelvin-Helmholtz timescale.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Origin of Planetary Systems; LPI-Contrib-1197
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    When Push Comes to Shove: Gap-opening, Disk Clearing and the In Situ Formation of Giant Planets (2004)
    In:  CASI
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    Publication Date: 2018-06-11
    Description: Here we investigate a scenario in which cores as small as a few Earth masses stall in the terrestrial planet region, but continue to grow as a result of the Type I migration of other Earth sized objects, taking place in a timescale approx. 10(exp 6) years similar to the disk clearing timescale (such migration may thus significantly reduce the accretion efficiency, particularly in the terrestrial planet region). Since the core may intercept such inwardly migrating objects (possibly by altering the surface density to the point that the object stalls within the core's feeding zone) or coalesce with neighboring cores, its growth may continue until it reaches a CCM. The question then arises whether such a core can accrete enough gas to become a Jovian-sized giant planet. In the limit of low opacity (such that the protoplanet s tidal torque fails to clear gas from its feeding zone in time to prevent its accretion), the final mass of the planet is given by the gaseous isolation mass (provided alpha is 〈 or approx. = 10(exp -4) and that the gas component dominates the planet's mass).
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Origin of Planetary Systems; LPI-Contrib-1197
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    Stardust Imaging of Comet Wild 2: First Look (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: On 2 January 2004 during its historic flight to return cometary dust samples to earth, the STARDUST spacecraft flew within the coma of comet Wild 2 and also took 72 images where the surface was resolved during the flyby. A combination of long and short exposures was used to observe the jets and the surface. Comet Surface: The images revealed a planetary body, one not having a significant atmosphere, quite different from any other such body seen from other spacecraft. Surface depressions, potentially a combination of craters and vents, were not bowl-shaped but typically had steep walls and flattened floors. One depression considered to be a vent, the source of a jet, had a depth to diameter ratio of approx.0.4, with near vertical walls. Jets: At least 10 to possibly 20 jets were active during the flyby. Some were traced back to the surface where they seem to originate from the near vertical walls of depressions (vents) that were facing the sun, having the highest solar insolation.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Stardust Mission; LPI-Contrib-1197
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    Topographic Evidence for Eruptive Style Changes and Magma Evolution of Small Plains-style Volcanoes on Earth and Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Topographic profiles and surface characteristics of small (5 - 25 km diameter) plains-style shield volcanoes on the eastern Snake River Plain (ESRP) provide a method to evaluate eruptive processes and magmatic evolution on Martian volcanic plains. The ESRP is an ideal place to observe Mars-like volcanic features where hundreds of small monogenetic basaltic shields dominate the volcanic-sedimentary depositional sequence, and numerous planetary analogues are evident: coalescent mafic shields, hydromagmatic explosive eruptions, the interaction of lava flows with surficial water and glacial ice, and abundant eolian sand and loess. Single flows cannot be correlated over great distances, and are spatially restricted. These relations are useful for planetary exploration when inferring volcanic evolutionary patterns in lava plains represented by numerous eruptive vents. High spatial resolution imagery and digital topographic data for Mars from MOC, MOLA, and THEMIS is allowing for improvements in the level of detail of stratigraphic mapping of fields of small (〈 25 km in diameter) volcanoes as well as studies of the morphological characteristics of individual volcanoes. In order to compare Mars and Earth volcanic features, elevation data from U.S.G.S. 10-meter digital elevation models (DEMs) and high-precision GPS field measurements are used in this study to generate approx. 20m spacing topographic profiles from which slope and surface morphology can be extracted. Average ESRP flank and crater slopes are calculated using 100 - 200 m spacing for optimum comparison to MOLA data, and to reduce the effects of surface irregularities.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Tectonism and Volcanism; LPI-Contrib-1197
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    GCM Simulations of Tropical Ice Accumulations: Implications for Cold-based Glaciers (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Each of the three Tharsis Montes shield volcanoes on Mars has fan-shaped deposits on their flanks. A detailed analysis of the multiple facies of the Arsia Mons deposits, coupled with field observations of polar glaciers in Antarctica, shows that they are consistent with deposition from cold-based mountain glaciers. Key features of these glaciers are: (1) they formed only on the western flank of each volcano, (2) enough ice accumulated to cause them to flow but without basal melting, (3) there were multiple advances and retreats, (4) the last major glaciation was more than several million years ago, (5) the areal extent of the deposits they left behind decreases northward, (6) together the deposits range in elevation from a low of 1.5 to a high of 8.5 km, and (7) there are no signs that significant accumulation is occurring today.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Polar Science and Exploration; LPI-Contrib-1197
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    Evaporation Rates for Liquid Water and Ice Under Current Martian Conditions (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: A number of studies have been concerned with the evaporation rates under martian conditions in order to place limits on the possible survival time of both liquid water and ice exposed on the surface of Mars. Such studies also aid in assessing the efficacy of an overlying layer of dust or loose regolith material in providing a barrier to free evaporation and thus prolong the lifetime of water in locations where its availability to putative living organisms would be significant. A better quantitative understanding of the effects of phase changes of water in the near surface environment would also aid the evaluation of the possible role of water in the formation of currently observed features, such as gullies in cliff walls and relatively short-term changes in the albedo of small surface areas ('dark stains'). Laboratory measurements aimed at refinement of our knowledge of these values are described here. The establishment of accurate values for evaporation rates and their dependence on the physical conditions of temperature, pressure and energy input, is an important benchmark for the further investigation of the efficacy of barriers to free evaporation in providing a prolonged period of survival of the water, particularly as a liquid.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Polar Science and Exploration; LPI-Contrib-1197
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  • 95
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    Internal Structure of the Southern Polar Cap of Mars and Formation Implications (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The surfaces of the Martian polar caps have been studied in detail but little is known about their internal structure. Exposures of the cap interior can be seen in the many troughs and scarps which incise them. The layered sequences visible in these topographic features have been known to exist for many years, however first order questions concerning the internal stratigraphy remain. We have identified a prominent bench forming layer near the top of the southern layered deposits. We have mapped its exposure in high-resolution MOC images on the eastern and western scarps. These images have been carefully registered to a MOLA derived DEM so topographic measurements along this bench can be extracted along with the location of each trace. What results are a set of measurements of the top of the bench forming layer in three dimensions. The top of this layer represents a distinct stratigraphic horizon. The prominent bench outcrops on both the eastern and western scarps which bound the highest portion of the southern layered deposits. Confirmation that these are two benches are indeed the same stratigraphic surface comes from the similarity of surrounding (nonbench forming) layers.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Polar Science and Exploration; LPI-Contrib-1197
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  • 96
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    Evidence for Possible Exposed Water Ice Deposits in Martian Low Latitude Chasms and Chaos (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: A light-toned interior layer deposit (ILD) on the floor of the deep martian depression Juventae Chasma is found to have a relatively high thermal inertia approx. 500 J m(exp -2) s(exp -1/2) K(exp -1). This could imply rock, but is also similar to the average value of thermal inertia found for north polar layered deposits. Furthermore, ILD-B is found to exhibit a bluff and terrace structure . A terrace structure arises naturally in model simulations of the sublimation of large ice deposits. Such a staircase terrain, of course, is a further characteristic of north polar layered terrain. Morphological similarity, thermal inertia in the range of thermal inertias of the north polar cap layered terrain, and relatively high albedo lead us to propose that the ILD-B may consist of residual water ice partially covered by, and perhaps mixed with, varying amounts of dust or sand. Other ILDs (A-C) are also found in Juventae Chasma. While these ILDs lack the close morphological resemblance to the north polar cap, they share many other common features and appear to be part of the same formation. Similar ILDs are found in chaotic terrain elsewhere in the martian tropics. This leads us to propose that water ice may exist in the martian tropics today and may be implicit in the formation of chaotic terrain.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Polar Science and Exploration; LPI-Contrib-1197
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    An Historical Search for Unfrozen Water at the Phoenix Landing Site (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The goal of this work is to explore the history of the high-latitude subsurface in the latitude range of the Phoenix landing site (65-75 deg. N). The approach is to use time-marching climate models to search for times, locations, and depths where thick films of unfrozen water might periodically occur. Thick films of unfrozen water (as distinct from ubiquitous monolayer water) are interesting for two reasons. First, multi-layer films of water may be bio-available. Second, patterned ground may require the occurrence of thick films of unfrozen water to facilitate the migration of particles and the development of excess pore ice, as reported by the Odyssey Gamma Ray Spectrometer (GRS) results. For the purposes of this work, we define conditions adequate to establish thick films of unfrozen water to be T greater than 268 K, and RH greater than 0.5. We start with the need to understand the atmospheric pressure. Because of the fact that we're looking at high latitudes, the seasonal cap buffers surface temperature for some part of the year. That directly affects the subsurface thermal regime, at least in the uppermost meter where we will be
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Polar Science and Exploration; LPI-Contrib-1197
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  • 98
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    Impact Crater Abundance of the Martian South Polar Layered Deposits from THEMIS Visible Imaging (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The polar layered deposits (PLD) of Mars have attracted considerable attention since their identification in Mariner 9 images, largely due to the possibility that these finely layered, volatile-rich deposits hold a record of recent eras in Martian climate history. The PLD have been a target of imaging and other sensors in the last several decades, but only recently has it been possible to obtain a moderately high resolution image map, using the visible sensor on 2001 Mars Odyssey's Thermal Emission Imaging System (THEMIS). THEMIS has acquired a 36 meter/pixel contiguous single-band visible image data set of the south polar layered deposits (SPLD), during the southern spring in 2003. The data will undoubtedly be applied to many problems in Mars polar studies. We use these images to further characterize the population of impact craters on the SPLD, and the implications of the observed population for the age and evolution of the SPLD.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars Polar Science and Exploration; LPI-Contrib-1197
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  • 99
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    H2O2 Synthesis Induced by Irradiation of H2O with Energetic H(+) and Ar(+) Ions at Various Temperatures (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: The detection of H2O2 on Jupiter's icy satellite Europa by the Galileo NIMS instrument presented a strong evidence for the importance of radiation effects on icy surfaces. A few experiments have investigated whether solar flux of protons incident on Europa ice could cause a significant if any H2O2 production. These published results differ as to whether H2O2 can be formed by ions impacting water at temperatures near 80 K, which are appropriate to Europa. This discrepancy may be a result of the use of different incident ion energies, different vacuum conditions, or different ways of processing the data. The latter possibility comes about from the difficulty of identifying the 3.5 m peroxide OH band on the long wavelength wing of the much stronger water 3.1 m band. The problem is aggravated by using straight line baselines to represent the water OH band with a curvature, in the region of the peroxide band, that increases with temperature. To overcome this problem, we use polynomial baselines that provide good fits to the water band and its derivative.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Icy Worlds: Moving and Grooving; LPI-Contrib-1197
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    Magnesium Isotopes in the Earth, Moon, Mars, and Pallasite Parent Body: High-Precision Analysis of Olivine by Laser-Ablation Multi-Collector ICPMS (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Magnesium isotopes potentially offer new insights into a diverse range of processes including evaporation and condensation in the solar nebula, melting and metasomatism in planetary interiors, and hydrothermal alteration [1,2,3,4]. Volatility-related Mg isotopic variations of up to 10 per mil/amu relative to a terrestrial standard have been found in early nebular phases interpreted as evaporation residues [1], and relatively large variations (up to 3 per mil/amu) in the terrestrial mantle have been reported recently [4]. In order to investigate possible differences in the nebular history of material contributing to the terrestrial planets, and to search for evidence of a high-temperature origin of the Moon, we have measured the magnesium isotopic composition of primitive olivines from the Earth, Moon, Mars, and pallasite parent body using laser-ablation multicollector ICPMS.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Terrestrial Planets: Building Blocks and Differentiation; LPI-Contrib-1197
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