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  • 1
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    Topography of the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50 degrees is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 279; 5357; 1686-92
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  • 2
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    Observations of the north polar region of Mars from the Mars orbiter laser altimeter (1998)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 282; 5396; 2053-60
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  • 3
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    The global topography of Mars and implications for surface evolution (1999)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 284; 5419; 1495-503
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  • 4
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    Crustal Structure of Mars from Mars Global Surveyor Topography and Gravity (2000)
    In:  Other Sources
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    Publication Date: 2017-10-02
    Description: In this analysis we invert global models of Mars' topography from Mars Orbiter Laser Altimeter (MOLA) and gravity from Doppler tracking obtained during the mapping mission of Mars Global Surveyor (MGS). We analyze the distribution of Martian crust and discuss implications for Mars' thermal history.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXI; LPI-Contrib-1000
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  • 5
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    Thermal history and evolution of the moon. (1973)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: In this work, theoretical lunar temperature models are computed taking into account different initial conditions to represent possible accretion models and various abundances of heat sources to correspond to different compositions. Differentiation and convection are simulated in the numerical computational scheme. Models of the thermal evolution of the moon that fit the chronology of igneous activity on the lunar surface, the stress history of the lunar lithosphere implied by the presence of mascons, and the surface concentrations of radioactive elements, involve extensive differentiation early in lunar history. This differentiation may be the result of rapid accretion and large-scale melting or of primary chemical layering during accretion. Differences in present-day temperatures for these two possibilities are significant only in the inner 1000 km of the moon and are not resolvable with presently available data.
    Keywords: SPACE SCIENCES
    Type: The Moon; 7; May-June
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  • 6
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    Thermal evolution of the moon. (1972)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The thermal history and current state of the lunar interior are investigated using constraints imposed by recent geological and physical data. Theoretical temperature models are computed taking into account different initial conditions, heat sources, differentiation and simulated convection. To account for the early formation of the lunar highlands, the time duration of magmatism and present-day temperatures estimated from lunar electrical conductivity profiles, it is necessary to restrict initial temperatures and abundances of radioactive elements. Successful models require that the outer half of the moon initially heated to melting temperatures, probably due to rapid accretion. Differentiation of radioactive heat sources toward the lunar surface occurred during the first 1.6 billion years. Temperatures in the outer 500 km are currently low, while the deep interior (radius less than 700 to 1000 km) is warmer than 1000 C, and is of primordial material.
    Keywords: SPACE SCIENCES
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  • 7
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    Density within the moon and implications for lunar composition (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A number of simple density models for the moon are discussed. The considered models are consistent with the lunar mass and moment of inertia, the latest information on the seismic velocity of the lunar crust and mantle, and assorted estimates of temperature in the lunar interior. New material presented includes the implications for density models of recent seismic evidence for a thin, high velocity layer beneath the lunar crust and for a zone of partial melting below 1000 km depth. The consequences of a dense, iron-rich central core are also explored.
    Keywords: SPACE SCIENCES
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  • 8
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    A Procedure for Determining the Nature of Mercury's Core (2001)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: We review past assertions that the determinations of the four parameters, C(20), C(22), theta, phi, are sufficient to determine the size and state of Mercury's core. C(20) and C(22) are gravitational harmonics, theta is Mercury's obliquity and phi is the amplitude of the forced, 88 day period libration in longitude. The upcoming MESSENGER orbiter mission to Mercury with onboard instrumentation capable of measuring these four parameters, and the possibility of precision measurements of Mercury's spin geometry with radar interferometry techniques make a reexamination of this proposal particularly relevant. The two necessary conditions on the core-mantle interaction for the experiment to work are: 1. The core must not follow the 88 day physical librations of the mantle. 2. The core must follow the mantle on the time scale of the 250,000 year precession of the spin in Cassini state 1. We shall assume these two conditions are satisfied to develop the method and later establish the constraints on the core viscosity for which they are satisfied. Proposed mechanisms of core mantle coupling other than a viscous coupling do not frustrate the first condition. The physical libration of the mantle about the mean resonant angular velocity arises from the periodically reversing torque on the permanent deformation as Mercury rotates relative to the Sun. Additional information is contained in the original extended abstract.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Mercury: Space Environment, and Surface and Interior; 73-74; LPI-Contrib-1097
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  • 9
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    On the density distribution in the moon. (1968)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Models for lunar density distribution consistent with available data on lunar physical properties
    Keywords: SPACE SCIENCES
    Type: ; YAL SOCIETY (
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  • 10
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    The Crust of the Moon as Seen by GRAIL (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-23
    Description: High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN6865 , Science (ISSN 0036-8075) (e-ISSN 1095-9203); 339; 6120; 671-675
    Format: application/pdf
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