Assessment of Mars Science and Mission Priorities (2003) / Chapter Skim
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2. Interior and Crustal Structure and Activity
2. Interior and Crustal Structure and Activity
Pages 9-17
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From page 9... ...
2. Mars had a magnetic field in the past, but there is no present global field, as shown by high-amplitude magnetic anomalies detected in the southern highlands of Mars by the Mars Global Surveyor (MGS)
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From page 10... ...
The ranges of estimated uncompressed densities are 3.8 to 3.9 g/cm3 for Mars and 4.4 to 4.5 g/cm3 for Earthy The moment-of-inertia factor measured for Earth is 0.3315.8 The difference in moment-of-inertia factors indicates that the concentration of mass toward the center of Mars is less than that of Earth. Earth's core size is well determined from seismic studies; thus, the measured moment-of-inertia factor for Earth directly constrains the ratio of the core density to the mantle density.
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From page 11... ...
The field seen in parts of the highlands is consistent with a crustal magnetization model made up of multiple quasi-parallel linear features with dimensions ~200 km in width, extending as far as 2000 km in length. Some workers interpret these highland areas as remnants of early "oceanic crust," reworked in places by subsequent major impacts and thermal events, but preserving elsewhere the magnetic imprint acquired when the crust formed by "sea floor spreading."20 Others consider that dike intrusions produced the magnetization patterns.2i Measurements made early in the MGS mission established unambiguously that Mars does not currently possess a significant global magnetic field, the estimated upper limit for a Mars dipole moment being ~2 x 10~8 A m2.22 The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Noachian epoch (~4 billion years ago)
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From page 12... ...
First, the gravity anomalies are explained as a result of the load of Tharsis volcanic rocks on an 100-km-thick elastic lithosphere with insignificant contribution from the deep interior.34 35 Second, the gravity and topography of the Tharsis Rise are interpreted as dynamic effects of mantle convection.36 A key insight from the MGS topographic data is that the plateau predates the formation of apparently fluvial channels. This suggests that the outpouring of lava to make the plateau may have released enough carbon dioxide to form an insulating atmosphere and sufficient water to form the channels and even an ocean.
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From page 13... ...
Though this planned experiment involves a minimal number of stations, it may accomplish several important goals, including constraining the size and state of the core, and determining the level of tectonic activity and the rate of meteroid impacts. This is an excellent start to the exploration of Mars's interior, and COMPLEX encourages NASA to support this and more comprehensive future seismic experiments.
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From page 14... ...
With the thickness and velocity profile through the crust determined at several locations, models could be constrained for the origin of the hemispheric dichotomy, thus improving our understanding of the geologic history of Mars. Receiver function analysis of passive seismic stations could constrain the crustal thickness and shallow mantle structure.
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From page 15... ...
Given the high priority that COMPLEX places on the range of objectives that seismic experiments could accomplish, the committee strongly recommends that NASA support passive seismic expenments.
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From page 16... ...
Roark, "The MOLA Topographic Signature at the Crustal Dichotomy Boundary Zone on Mars," Geophysical Research Letters 25: 44094412, 1998.
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From page 17... ...
Stevenson, "Influence of Early Plate Tectonics on the Thermal Evolution and Magnetic Fields of Mars," Journal of Geophysical Research 105: 11969-11980, 2000.
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