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  • Weitere Quellen  (13)
  • Lunar and Planetary Science and Exploration  (10)
  • ASTROPHYSICS  (2)
  • Solar Physics  (1)
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  • Weitere Quellen  (13)
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  • 1
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    The evolution of topography on a comet (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The evolution of cometary surface topography is presently modeled in terms of a focusing of thermal energy due to topographical concavity. The model encompasses incident sunlight, shadowing, molecular sublimation, and mutual radiative heating by the walls of a circle-segment cross section trench, which has a 'lensing' effect. After a large number of perihelion passages, the net effect of trench bottom sublimation losses will be the accentuation of topographical concavities. The comet surface sublimation, comet-splitting, and comet surface jet-formation consequences of this model are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus (ISSN 0019-1035); 72; 128-134
    Format: text
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  • 2
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    Evolution of topography on comets. II - Icy craters and trenches (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The determination of the effects of topography on the sublimation rates of comets and other icy bodies is presently approached via a model of ice heating and sublimation from topographical features. The energy balance equation is solved for cylindrical trenches and spherical craters; the model encompasses shadowing, solar heating, the trapping of thermal radiation and sublimed gas molecules, and reflection of sunlight within the cavity. Generally, an enhancement is found in the net sublimation rate for trenches and craters farther from the sun than some critical distance which depends on the albedo.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus (ISSN 0019-1035); 85; 205-215
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  • 3
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    Early Results from the Odyssey THEMIS Investigation (2003)
    In:  CASI
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    Publikationsdatum: 2017-10-02
    Beschreibung: The Thermal Emission Imaging System (THEMIS) began studying the surface and atmosphere of Mars in February, 2002 using thermal infrared (IR) multi-spectral imaging between 6.5 and 15 m, and visible/near-IR images from 450 to 850 nm. The infrared observations continue a long series of spacecraft observations of Mars, including the Mariner 6/7 Infrared Spectrometer, the Mariner 9 Infrared Interferometer Spectrometer (IRIS), the Viking Infrared Thermal Mapper (IRTM) investigations, the Phobos Termoscan, and the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). The THEMIS investigation's specific objectives are to: (1) determine the mineralogy of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify future landing sites likely to represent these environments; (2) search for thermal anomalies associated with active sub-surface hydrothermal systems; (3) study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties; (4) investigate polar cap processes at all seasons; and (5) provide a high spatial resolution link to the global hyperspectral mineral mapping from the TES investigation. THEMIS provides substantially higher spatial resolution IR multi-spectral images to complement TES hyperspectral (143-band) global mapping, and regional visible imaging at scales intermediate between the Viking and MGS cameras.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: Lunar and Planetary Science XXXIV; LPI-Contrib-1156
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  • 4
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    MAVEN - Mars Atmosphere and Volatile EvolutioN Mission (2011)
    In:  CASI
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    Publikationsdatum: 2019-07-19
    Beschreibung: NASA's MAVEN mission (to be launched in late 2013) is the first mission to Mars devoted to sampling all of the upper atmosphere neutral and plasma environments, including the well-mixed atmosphere, the exosphere, ionosphere, outer magnetosphere and near-Mars solar wind. It will fill in some measurement gaps remaining from the successful Mars Global Surveyor and the on-going Mars Express missions. The primary science objectives of MAVEN are: 1. Provide a comprehensive picture of the present state of the upper atmosphere and ionosphere of Mars; 2. Understand the processes controlling the present state; and 3. Determine how loss of volatiles to outer space in the present epoch varies with changing solar condition - EUY, solar wind and interplanetary magnetic field measurements will provide the varying solar energy inputs into the system. Knowing how these processes respond to the Sun's energy inputs in the current epoch will provide a framework for projecting atmospheric processes back in time to profile MARS' atmospheric evolution and to explore "where the water went", A description will be given of the science objectives, the instruments, and the current status of the project, emphasizing the value of having collaborations between the MAVEN project and the Mars upper atmosphere science community.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC.ABS.5704.2011 , Asia Oceania Geosciences Society 2011; Aug 08, 2011 - Aug 12, 2011; Taipei; Taiwan, Province of China
    Format: application/pdf
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  • 5
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    Solar Wind Induced Waves in the Skies of Mars: Ionospheric Compression, Energization, and Escape Resulting from the Impact of Ultralow Frequency Magnetosonic Waves Generated Upstream of the Martian Bow Shock (2018)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Using data from the National Aeronautics and Space Administration Mars Atmosphere and Voltatile EvolutioN and the European Space Agency Mars Express spacecraft, we show that transient phenomena in the foreshock and solar wind can directly inject energy into the ionosphere of Mars. We demonstrate that the impact of compressive ultralow frequency waves in the solar wind on the induced magnetospheres drive compressional, linearly polarized, magnetosonic ultralow frequency waves in the ionosphere, and a localized electromagnetic "ringing" at the local proton gyro frequency. The pulsations heat and energize Ionospheric plasmas. A preliminary survey of events shows that no special upstream conditions are required in the interplanetary magnetic field or solar wind. Elevated ion densities and temperatures in the solar wind near to Mars are consistent with the presence of an additional population of Martian ions, leading to ion-ion instabilities, associated wave-particle interactions, and heating of the solar wind. The phenomenon was found to be seasonal, occurring when Mars is near perihelion. Finally, we present simultaneous multipoint observations of the phenomenon, with the Mars Express observing the waves upstream, and Mars Atmosphere and Voltatile EvolutioN observing the response in the ionosphere. When these new observations are combined with decades of previous studies, they collectively provide strong evidence for a previously undemonstrated atmospheric loss process at unmagnetized planets: ionospheric escape driven by the direct impact of transient phenomena from the foreshock and solar wind.
    Schlagwort(e): Solar Physics
    Materialart: GSFC-E-DAA-TN62778 , Journal of Geophysical Research: Space Physics (ISSN 2169-9402) (e-ISSN 2169-9380); 123; 9; 7241-7256
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  • 6
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    The Twisted Configuration of the Martian Magnetotail: MAVEN Observations (2018)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45deg twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross-tail current sheet is rotated away from the expected location for a Venus-like induced magnetotail based on nominal IMF draping. Data-model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC-E-DAA-TN60525 , Geophysical Research Letters (ISSN 0094-8276) (e-ISSN 1944-8007); 45; 10; 4559-4568
    Format: text
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  • 7
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    Remote Sensing of Planetary Surfaces (2001)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-10
    Beschreibung: Our efforts have been focused on understanding the physical properties of planetary surfaces using remote sensing techniques. Specific application has been to the surfaces of the Moon and Mars. Our approach has been to use thermal-infrared emission and radar reflectance and scattering as a way of exploring the decimeter-scale structure of these surfaces. At this scale, the techniques are sensitive to physical parameters such as the average or effective particle size of surface materials, the degree of induration or physical bonding between individual regolith grains, and the abundance of rocks of different sizes resting on or admixed in to the surface. The results are relevant to understanding the geological processes that have affected the surface and, in the case of Mars, determining site safety and scientific relevance for planning upcoming lander, rover, and sample-return spacecraft missions. Specific results are discussed below, and publications that have resulted are listed at the end.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Format: application/pdf
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  • 8
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    MAVEN Navigation During the First Mars Year of the Science Mission (2016)
    In:  Other Sources
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    Publikationsdatum: 2020-01-13
    Beschreibung: No abstract available
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: JPL-CL-16-4046 , AIAA/AAS Astrodynamics Specialist Conference; Sep 12, 2016 - Sep 15, 2016; Long Beach, CA; United States
    Format: text
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  • 9
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    Electron Energetics in the Martian Dayside Ionosphere: Model Comparisons with MAVEN Data (2016)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: This paper presents a study of the energetics of the dayside ionosphere of Mars using models and data from several instruments on board the Mars Atmosphere and Volatile EvolutioN spacecraft. In particular, calculated photoelectron fluxes are compared with suprathermal electron fluxes measured by the Solar Wind Electron Analyzer, and calculated electron temperatures are compared with temperatures measured by the Langmuir Probe and Waves experiment. The major heat source for the thermal electrons is Coulomb heating from the suprathermal electron population, and cooling due to collisional rotational and vibrational CO2 dominates the energy loss. The models used in this study were largely able to reproduce the observed high topside ionosphere electron temperatures (e.g., 3000 K at 300 km altitude) without using a topside heat flux when magnetic field topologies consistent with the measured magnetic field were adopted. Magnetic topology affects both suprathermal electron transport and thermal electron heat conduction. The effects of using two different solar irradiance models were also investigated. In particular, photoelectron fluxes and electron temperatures found using the Heliospheric Environment Solar Spectrum Radiation irradiance were higher than those with the Flare Irradiance Spectrum Model-Mars. The electron temperature is shown to affect the O2(+) dissociative recombination rate coefficient, which in turn affects photochemical escape of oxygen from Mars.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC-E-DAA-TN40365 , Journal of Geophysical Research: Space Physics (ISSN 2169-9380) (e-ISSN 2169-9402); 121; 7; 7049–7066
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  • 10
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    Photoelectrons and Solar Ionizing Radiation at Mars: Predictions Versus MAVEN Observations (2016)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Understanding the evolution of the Martian atmosphere requires knowledge of processes transforming solar irradiance into thermal energy well enough to model them accurately. Here we compare Martian photoelectron energy spectra measured at periaps is by Mars Atmosphere and Volatile Evolution MissioN (MAVEN) with calculations made using three photoelectron production codes and three solar irradiance models as well as modeled and measured CO2 densities. We restricted our comparisons to regions where the contribution from solar wind electrons and ions were negligible. The two intervals examined on 19 October 2014 have different observed incident solar irradiance spectra. In spite of the differences in photoionization cross sections and irradiance spectra used, we find the agreement between models to be within the combined uncertainties associated with the observations from the MAVEN neutral density, electron flux, and solar irradiance instruments.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC-E-DAA-TN40352 , Journal of Geophysical Research (ISSN 0148-0227) (e-ISSN 2156-2202); 121; 9; 8859-8870
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