Water Ice from Mars and the Moon
Water ice and other volatiles are not only vital to sustaining human settlement in space, but hydrogen and oxygen extracted from water by hydrogen-oxide reactions can also be used as propellants on interplanetary missions. Water ice occurs in abundance on Mars in polar ice caps, as well as in shallow permafrost. Martian polar caps, 2.7 and 3.1 km thick at the north and south poles, respectively, have an ice core overlain by carbon dioxide frost that sublimates during spring. The ice layers are interbedded with numerous thin dust layers that record global cycles of dust storms. Martian permafrost, which appears to hold more water ice than the poles, occurs in a wide variety of forms, including collapse structures, polygonal terrain, and pingoes with morphologies similar to those of terrestrial periglacial features. Water ice may also occur on the Moon at the north and south poles, judging from hydrogen neutron scattering signatures from Clementine and Lunar Prospector missions. Given radar reflectivity signatures, lunar ice probably does not occur in extensive sheets at the surface, but, rather, in disseminated form in the shallow (<40 cm) regolith in floors of permanently shadowed craters. Estimates of the ice resource, hypothesized to have accumulated from meteoritic and cometary impacts, range from 10 to 300 million metric tons (3 to 90 billion gallons). An important objective of the Lunar Reconnaissance Orbiter mission, planned for launch in 2009, will be to map the distribution of, and quantify, the lunar ice resource.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009