Computer Science – Sound
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.h11a1254c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #H11A-1254
Computer Science
Sound
0702 Permafrost (0475), 0994 Instruments And Techniques, 1829 Groundwater Hydrology, 5419 Hydrology And Fluvial Processes, 6225 Mars
Scientific paper
The abundance and distribution of water on Mars has important implications for understanding the planet's geologic, hydrologic, and climatic history; the potential origin and continued survival of life; and the accessibility of a critical in-situ resource for sustaining future human explorers. For this reason, the search for water has become a key objective of NASA's Mars Exploration Program. Evidence of water, both past and present, is found almost everywhere, but most persuasively in the form of the planet's outflow channels -- broad scoured depressions hundreds of kilometers long that emerge abruptly from large areas of collapsed and disrupted terrain, the apparent result of a massive release of subpermafrost groundwater. Based on a conservative estimate of the volume of water required to erode the channels, Carr (Icarus, 68, 187-216, 1986) has estimated that Mars may possess a total planetary inventory of water equivalent to a global ocean 0.5 - 1 km deep. Of this global inventory, ~0.000001% is found in the atmosphere, while ~5-10% is visible as ice in the perennial polar caps. This leaves ~90-95% of the planetary inventory of water unaccounted for, the vast bulk of which is believed to reside, as ground ice and groundwater, within the planet's crust. Theoretical and geomorphic approaches to assessing the current distribution and state of subsurface water on Mars face numerous obstacles -- thus geophysical techniques hold the most promise. The first such investigation, the Gamma-Ray Neutron Spectrometer aboard the Mars Odyssey Orbiter, arrived at Mars in 2001. It revealed that the top half-meter of the Martian regolith is rich in hydrogen at latitudes above ~40-degrees, an observation consistent with the presence of near-surface ground ice. Assessing the distribution of water at greater depths (up to several kilometers) is one of the chief objectives of the MARSIS experiment on ESA's Mars Express spacecraft. MARSIS is a low-frequency (1-5 MHz) orbital radar sounder that began collecting its first data in June of this year. Several other geophysical investigations to search for water are either en route or planned over the next decade. In this talk, the capabilities and limitations of these investigations are discussed, as well as a proposed strategy for the types of investigations, and sequence of missions, that will provide the most direct, cost-effective, and technically capable approach for identifying the 3-dimensional distribution and state of water on Mars.
Clifford Stephen M.
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