Mar 07 2009
The search for the lost lunar lakes continues into the 21st Century! This adventure, worthy of Indiana Jones, will strongly influence human expansion into the cosmos. If they are found, the lakes will be the key to lunar development and human settlement of the inner solar system during the 2015 Maslow Window. If not, hydrogen may have to be imported to support future lunar science, industry, and tourism.
Today, the search for the lost lunar lakes involves a beautiful international collaboration between India, NASA, and others. The Chandrayaan-1 — India’s first mission to the Moon — was launched by the ISRO on October 22, 2008 using its 4-stage PSLV rocket. The vehicle achieved lunar orbit on November 8. A week later India became only the 4th entity reach the Moon’s surface (after former Soviet Union, U.S., and European Space Agency) when its Moon Impact Probe hit near the Moon’s south pole. The MIP’s impact released debris from near the crater Shackleton that may provide clues to the presence of lunar water ice. You may remember that Shackleton is a famous name associated with the “Heroic Age” of Antarctic exploration during the early 20th Century Peary/Amundsen Maslow Window.
Happily hitching a ride on Chandrayaan-1 is NASA’s Mini-SAR, a synthetic aperature radar expected to help search “the inside of (polar) craters for water ice” (Space News, 1/26/09). According to planetary scientist Benjamin Bussey of the Mini-SAR program office at Johns Hopkins University, this is “the only way to explore such areas.”
The birth of the first Space Age stimulated serious interest in the lost lunar lakes when 3 Caltech scientists proposed in 1961 that water and other volatiles could be trapped in eternally shadowed crater floors near the Moon’s poles (K. Watson, B.C. Murray, H. Brown, J. Geophys. Res. 66, 3033 (1961)), because of the Moon’s low axial tilt (only 1.5 deg vs. Earth’s 23.5 deg). Their model indicated that lunar polar cold traps would have temperatures below 100 degrees K (- 173 deg C) and could retain ices for billions of years.
Ten years after the Apollo Moon landings, UC San Diego chemist James Arnold commented that like the lunar lakes, “an important paper by Watson, Murray, and Brown (1961) seems to have been lost.” The desiccated character of the returned Moon rocks showed that any water on the Moon probably came from elsewhere, so Arnold suggested water-rich meteors and icy comets.
In 2007, the National Research Council identified the lunar (and Mercurian) polar microenvironments as “unique in the solar system” because of their potential for illuminating “the volatile flux over the latter part of solar system history.” The NRC recognizes that “cold trapping of hydrogen-bearing volatiles does occur,” but their identity (e.g., water vs. hdrogen) and sources (e.g., comets vs. lunar outgassing) are currently unknown. However they see strong links between “lunar resource utilization, science, and human exploration.”
The first really successful searcher for the lost lunar lakes was Dr. Alan Binder, who led Lunar Prospector science in 1998. According to the NRC, LP detected a “distinct neutron albedo deficit over the poles.” This implies significant concentrations of hydrogen, possibly in the form of patchy ice, but most likely not at the immediate surface.
In an email to me on March 4, Alan commented that the LP discovered “an enhancement of up to 1700 ppm of hydrogen in the permanently shadowed craters of the north and south poles over the 50 to 100 ppm in the lower latitudes.” At this point, “the theoretical arguments favor … water ice crystal, at a very low mixing ratio of around just 1%, (but) we have no proof that the hydrogen is … not just enhanced deposits of solar wind hydrogen.”
Because of the low mixing ratio of 1%, Dr. Binder believes that “a spacecraft radar/radio experiment will not detect the ‘water ice’,” so he points to the upcoming LCROSS repeat of his LP impact experiment. According to NASA, this year LCROSS will target a shadowed lunar polar crater with two large impactors; the resulting debris cloud will be analyzed for the presence of lunar water, hydrocarbons, and hydrated minerals. Launch is scheduled for April 24.
The search for the lost lunar lakes intensifies!