From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.
Bureau Seminar, January 15, 2010
The Search For Water On The Moon
Link to streaming video: available 01.15.2010 at 8:25am
Bureau of Economic Geology
Although water on the Moon was only recently been verified from the LCROSS (Lunar CRater Observation and Sensing Satellite) mission in 2009, it was hypothesized to occur in cold traps in polar regions nearly 50 years ago (Watson et al. 1961). Water is an important resource in space exploration. In addition to sustaining human settlements, hydrogen and oxygen in water are sources for rocket propellants that can be manufactured on the Moon, contributing to overall space-transportation costs. Indications of high hydrogen levels at the poles came from the Clementine mission in 1994, based on polarized radar signatures from deeply shadowed craters near the Moon’s south pole. Moreover, neutron spectroscopy data from the 1999 Lunar Prospector mission revealed elevated levels of polar hydrogen. A leading explanation for these hydrogen anomalies is that water-ice deposits and other volatiles accumulated as ejecta from lunar impacts from water- and volatile-rich comets and asteroids that settled in areas of permanent shadow at or near the Moon’s poles in the last 3 billion years. Although volatiles deposited on the lunar surface rapidly sublimate in sunlit areas where the temperature can exceed 100ºC, they are stable in areas of permanent shadow where the temperature is slightly above absolute zero. The Moon’s low obliquity (~1.5º) results in significant shadowed and weakly illuminated areas near the north and south poles. Bussey et al. (2003) estimate that ~2,900 mi2 (~7,500 km2) of such shadowed areas occur within 12º of the north pole and ~2,500 mi2 (~6,500 km2) of permanent shadow exist within 12º of the south pole. However, radar-scattering properties of many shadowed areas, consistent with rugged inner-crater walls and impact-related ejecta, suggest that water ice may occur as disseminated grains at 1 to 2% abundance in the shallow regolith.