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  • 1
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    Phosphates in pallasite meteorites as probes of mantle processes in small planetary bodies (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Trace element analyses of the phosphates minerals in stony-iron pallasite meteorites are used here to investigate the magmatic history of the silicate portions of pallasites. In Eagle Station and seven other pallasites, the phosphates have relatively low concentrations of REEs and are strongly enriched in heavy relative to light REE. These patterns are consistent with formation of phosphate by subsolidus reactions between metal and silicate, in which phosphate inherits the REE pattern of olivine. In Springwater and Santa Rosalia, calcium-rich phosphates have higher concentrations of REE, are enriched in light relative to heavy REE, and have negative europium anomalies. These patterns are consistent with crystallization of phosphate from a europium-depleted chondritic liquid. This is unlikely to have happened near the base of the differentiating parent-body mantle; it suggests that some pallasites may come from regions of their parent bodies much nearer the surface than the core-mantle boundary.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 353; 637-640
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  • 2
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    Duration of liquid water habitats on early Mars (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The duration of ice-covered lakes after the initial freezing of the early Mars is presently estimated via a climate model whose critical parameter is the existence of peak seasonal temperatures above freezing, and in which the variability of insolation is included. Under conditions in which meltwater was supplied by an ice source, it is found that water habitats could have been maintained under relatively thin ice sheets for as many as 700 million years after the onset of below-freezing global temperatures. The duration of such habitats on the early Mars therefore exceeds the upper limit of the time envisioned for the emergence of aquatic life on earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 90; 214-221
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  • 3
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    Rheological analyses of lava flows on Mars (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Researchers obtained 183 profiles of lava flows on Mars using photoclinometry. These photoclinometric profiles were leveled by adjusting them until the levee crests or bases had the same elevations (depending on the situation). Here, researchers report some of the results of their analysis of 27 flows on the flanks of Alba Patera (3 flows), near the summit of Ascraeus Mons (6 flows), the flanks of Arsia Mons (3 flows), and the flanks of Olympus Mons (15 flows). Results suggest that the flows examined to date are not felsic or ultramafic; rather, they probably range from basalts to basaltic andesites. Thus, the suggestion that flows on Olympus Mons and elsewhere may be more silicic than Hawaiian basalts is supported by the researchers' results. These suggestions are testable with suitable measurements of silica contents of the flows.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 170-171
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  • 4
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    Interactions of tectonic, igneous, and hydraulic processes in the North Tharsis Region of Mars (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Recent work on the north Tharsis of Mars has revealed a complex geologic history involving volcanism, tectonism, flooding, and mass wasting. Our detailed photogeologic analysis of this region found many previously unreported volcanic vents, volcaniclastic flows, irregular cracks, and minor pit chains; additional evidence that volcanic tectonic processes dominated this region throughout Martian geologic time; and the local involvement of these processes with surface and near surface water. Also, photoclinometric profiles were obtained within the region of troughs, simple grabens, and pit chains, as well as average spacings of pits along pit chains. These data were used together with techniques to estimate depths of crustal mechanical discontinuities that may have controlled the development of these features. In turn, such discontinuities may be controlled by stratigraphy, presence of water or ice, or chemical cementation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 73-74
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  • 5
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    Have graben wall scarps accumulated sand and dust on Mars? (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Grabens are linear fault bounded troughs that are extremely abundant on Mars (about 7000 cover the Western Hemisphere). Analysis of lunar and Martian grabens as well as analogous structures on Earth indicates that grabens form under extension when the crust is pulled apart. On Mars, topographic maps are not of sufficient resolution to measure graben wall slopes. Seismic shaking on Mars might be capable of reducing 60 deg fault scarps to an angle of repose. Some other process must be responsible for further reducing graben wall slopes. If the deposition of sand and dust along graben walls is responsible for their extremely low slopes, then a variety of implications are possible. Sand and/or dust movement and deposition is ubiquitous in grabens over most of Mars, as similar looking grabens are found over the entire Western Hemisphere and this requires a plentiful supply of sand or dust. If the material that accumulates is of low density and cohesion, attempts to traverse graben walls might be difficult. Rimless shallow depressions could be more effective sinks for sand and dust on Mars than has been realized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Ames Research Center, Sand and Dust on Mars; p 20
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  • 6
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    Effects of Martian dust on power system components (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Before large power systems for manned exploration of the Martian surface can be put into place, it must be determined how their performance will be affected by the Martian environment. A program was started to assess the impact of these environmental factors on power system performance, and to find ways to mitigate the degradative effects. The effects of blowing dust on photovoltaic (PV) and radiator surfaces is studied. Extensive use was made of the Martian Surface Wind Tunnel (MARSWIT) located at NASA-Ames to simulate Martian winds. Two basic types of experiment sets were run. In the first, the threshold clearing velocity of dust deposited on PV coverslip material and high emissivity radiator materials in clear Martian-like winds was examined. In the second, dust was dropped near the inlet of the wind tunnel and the winds were allowed to carry the dust past the samples, simulating a dust storm. A summary of results is given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Ames Research Center, Sand and Dust on Mars; p 18-19
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  • 7
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    Concepts for manned lunar habitats (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The design philosophy that will guide the design of early lunar habitats will be based on a compromise between the desired capabilities of the base and the economics of its development and implantation. Preferred design will be simple, make use of existing technologies, require the least amount of lunar surface preparation, and minimize crew activity. Three concepts for an initial habitat supporting a crew of four for 28 to 30 days are proposed. Two of these are based on using Space Station Freedom structural elements modified for use in a lunar-gravity environment. A third concept is proposed that is based on an earlier technology based on expandable modules. The expandable modules offer significant advantages in launch mass and packaged volume reductions. It appears feasible to design a transport spacecraft lander that, once landed, can serve as a habitat and a stand-off for supporting a regolith environmental shield. A permanent lunar base habitat supporting a crew of twelve for an indefinite period can be evolved by using multiple initial habitats. There appears to be no compelling need for an entirely different structure of larger volume and increased complexity of implantation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-104114 , NAS 1.15:104114
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  • 8
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    Impact experiments. III - Catastrophic fragmentation of aggregate targets and relation to asteroids (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: An experimental study is conducted of collisions employing artificial aggregates as targets, in order to ascertain the fragmentation characteristics of weakly bonded bodies that consist of stronger constituent particles, such as loosely aggregated planetesimals. It is established that weakly bonded aggregate bodies may exhibit unexpectedly high impact strengths due to constituent particles' energy dissipation. The cumulative size distributions of fragments that are larger than the constituent grains form power-law segments resembling those formed by the fragmentation of homogeneous targets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 94; 283-298
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  • 9
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    Scientific Rationale and Requirements for a Global Seismic Network on Mars (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Following a brief overview of the mission concepts for a Mars Global Network Mission as of the time of the workshop, we present the principal scientific objectives to be achieved by a Mars seismic network. We review the lessons for extraterrestrial seismology gained from experience to date on the Moon and on Mars. An important unknown on Mars is the expected rate of seismicity, but theoretical expectations and extrapolation from lunar experience both support the view that seismicity rates, wave propagation characteristics, and signal-to-noise ratios are favorable to the collection of a scientifically rich dataset during the multiyear operation of a global seismic experiment. We discuss how particular types of seismic waves will provide the most useful information to address each of the scientific objectives, and this discussion provides the basis for a strategy for station siting. Finally, we define the necessary technical requirements for the seismic stations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-188806 , NAS 1.26:188806 , LPI-TR-91-02 , May 07, 1990 - May 09, 1990; Morro Bay, CA; United States
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  • 10
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    Fassaite composition trends during crystallization of Allende Type B refractory inclusion melts (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Major-, minor-, and trace-element zoning trends in fassaite from Type B1 and B2 inclusions from the Allende meteorite are defined by using electron and ion microprobe data. Fassaite/liquid distribution coefficients are calculated for many of the lithophile elements, and evidence for and against the presence of relict fassaite in these inclusions is discussed. Major-element zoning in fassaite in Type B CAIs is found from Ti-, V-, Sc-rich cores to relatively Mg-, Si-rich rims. Trace elements that are incompatible in this fassaite are Nb (effective fassaite/liquid distribution = 0.29), Y(0.52), Ta(0.34), Th(0.053), U(0.4), and rare earth elements (0.31-0.48), while compatible trace elements are Zr(1.1) and Hf(1.5). Rare-earth-elements (RRE) abundances in fassaite are found to be controlled by crystal/liquid fractionation. Candidates for relict fassaite grains are discovered: Ti-, Sc-rich, REE-poor crystals enclosed in melilite in the mantle of TS34.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 55; 2635-265
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