Right now I'm enduring winter in snow-encrusted Boston, but my head is in The Woodlands, Texas, where more than 1,200 researchers have gathered for the annual Lunar and Planetary Science Conference. The LPSC is always a 'best bet" for hearing new discoveries about the solar system, and yesterday got off with a bang as scientists discussed water ice on the Moon — not whether it's there, but how much of it might be lying around.
I think 2009 will be remembered as the year we finally convinced ourselves that water is present on the Moon. Planetary scientists have speculated about its existence there for decades, because some craters at the lunar poles never, ever see sunlight and thus might serve as "cold traps" where ice (arriving on comets, presumably) could remain stable. But last year three lunar spacecraft returned results that have made the case for lunar ice all but certain.
The most dramatic findings came after NASA "bombed" the polar crater Cabeus last October 9th with its Lunar Crater Observation and Sensing Satellite (LCROSS) — though it took mission scientists a while to certify that the impact had dredged up water from the crater's shadowed floor.
It turns out there's more to this story: Yesterday NASA-Ames scientist Anthony Colaprete announced that, in addition to water, LCROSS had unearthed a whole kettle of volatile compounds in the plume of impact debris that rose from Cabeus. So far the tally includes sulfur dioxide (SO2), methanol (CH3OH), and the curious organic molecule diacetylene (H2C4).
Last year scientists also realized that whiffs of water cling to much of the lunar surface. An instrument built by American scientists but carried on India's Chandrayaan 1 spacecraft found the spectroscopic signature of water and hydroxyl (OH) ions over much of the Moon. Carlé Pieters, the Brown University researcher whose team designed the Moon Mineralogy Mapper (M3), had fortuitously extended its near-infrared coverage enough to record 2.8 and 3.0 microns, where the OH and water molecules have telltale absorptions.
Yesterday another Chandrayaan 1 instrument made a splash at LPSC, so to speak. Paul Spudis (Lunar and Planetary Institute) announced that NASA's Mini-SAR instrument had found evidence for water ice in more more than 40 small craters near the Moon's north pole. (Any water ice is not going anywhere soon — the Diviner instrument aboard NASA's Lunar Reconnaissance Orbiter finds that the interiors of these craters are the coldest locations ever measured in the solar system.)
The craters range in size from 1 to 9 miles (2 to 15 km), and according to a NASA press release the lunar stash could total up to 600 million tons of ice, depending on its thickness within each crater.
Utilizing a compact synthetic aperture radar, Mini-SAR detects changes in the polarization of radio waves reflected off the lunar surface. Water ice is transparent to radio energy and causes the radar pulses to be scattered multiple times, creating a distinctive polarization echo. Spudis thinks the deposits inside some polar craters could be nearly pure ice.
If he's right, think of the potential for lunar tourism! Imagine a cozy chalet perched atop the rim of a lunar crater, basking in a perpetual lunar sunset and with the resplendent Earth periodically bobbing into view from behind a distant peak. Then you jump into your super-insulated space suit, slap on some sticks, and schuss straight down the inner rim until you bottom out.
But watch out for those lunar moguls — in space, no one can hear you "screaming starfish."