LCROSS Found Water Ice

Mosaic of the Lunar south pole from Clementine images (NASA).

The LCROSS Science team held a briefing at 9AM PST today with results from the October 9th impact. Here's the summary of the content. They found ice. Previously, Lunar Prospector found hydrogen, Cassini detected water and hydroxyl (OH), and Chandrayaan found significant amounts of both water and OH present globally in hydrous minerals and as monolayers adsorbed on the surface of grains in the regolith. Those instruments were only able to examine the top few millimeters of the lunar surface. The LCROSS impact excavated to a depth of several meters in a permanently shadowed crater, and the science team says they've found large amounts of water in the impact plume -- too much, they think, to be solely due to water on the surface of mineral grains. It looks like the Moon may have a hydrologic cycle of sorts, with low concentrations in the regolith that increase towards higher latitudes and culminate in ice trapped in the permanently shadowed craters at the poles.

I posted on lunar water last month, but I'll recap. Lunar water may come from impactors, especially comets. It may come from the solar wind interaction with regolith. It is possible that water comes from degassing of the lunar interior -- we know that some water is present in the lunar interior because it has been found in volcanic samples returned by Apollo missions. My money is on the comets providing the bulk of it.

The science team is working to constrain the possible abundances of ethanol, hydrocarbons, and other chemical species. Apparently, ground-based observers of the LCROSS plume detected Na (Na is generally depleted on the Moon because it's volatile, so it makes sense to find it with water and other volatiles). We'll see detailed news reports later today and journal articles are on the way.