Computer Science – Sound
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p23a1614c&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P23A-1614
Computer Science
Sound
[5422] Planetary Sciences: Solid Surface Planets / Ices, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The Medusae Fossae Formation (MFF) consists of a number of distinct, friable, highly eroded, near-equatorial deposits, extending from Elysium to Amazonis Planitia, that are up to 3 km thick and cover a total area of 2x10^6 km^2. Proposed origins of the MFF have included everything from paleopolar deposits, whose presence reflects a prior location of the planet’s spin axis, to dry, high porosity volcanic ash. Radar sounding investigations of the deposits indicate that they have a dielectric constant of 2.9, consistent with either high porosity lithic materials or a large volumetric content of water ice. Here we consider the thermal and volatile response of an ice-rich crust to burial by an initially dry porous mantle of sediment or volcanic ash. Given reasonable values of surface temperature ( 200 - 220 K), effective pore size (1-10 μm), mantle porosity (20-50%), thermal conductivity (0.05 - 2 W m^{-1} K^{-1}), and global heat flow (15-30 mW m^{-2}), we find that the thermal reequilibration of the crust, following deposition, will cause a migration of the local crustal cold-trap (lowest mean annual temperature) from an initial position several meters below the original surface to a final position, at an approximately equal depth, a few meters below the surface of the mantle. This upward displacement of the local cold-trap results in the thermal redistribution of the underlying ground ice at a rate sufficient to saturate the available pore space in an initially dry 100 m-thick mantle within 10^7 - l0^8 years (and a 1 km-thick mantle, in a time span just several times longer). The results of this analysis indicate that even a small change in crustal temperature can exert a strong influence on the transport, stability, and ultimate distribution of subsurface H20. In particular, it demonstrates that through the process of thermal vapor diffusion, an initially volatile-poor depositional mantle, overlying an ice-rich crust, may (on a geologically short time scale) become quickly charged with ice - a fact that is likely to have important implications for reconciling the geologic evidence for extensive resurfacing on Mars with the widespread geomorphic evidence for the occurrence of ice within the near-surface crust. It also suggests that, even if the MFF deposits were initially dry, they may have become charged with ice in a geologically short span of time.
Clifford Stephen M.
Heggy Essam
Lasue Jeremie
Le Gall A. A.
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