It used to be that journalists joked about the multiple times that water was “discovered” for the first time on Mars. So when I heard that there would be an ad-hoc “water on the moon” press event today at LPSC, I wondered if I would hear about yet another wonderful watery lunar discovery.
To review: There has been an exciting flurry of discoveries that began in September, just as LRO was settling into orbit and finding hints that water lay in the frigid, permanently shadowed craters of the Moon’s north and south pole.
Just a week later, an instrument on India’s Chandrayaan-1 satellite showed that if scientists had just been looking a little more carefully in the near-infrared, they would have found a spectral signature for water and hydroxyl, right under their noses, distributed across nearly all latitudes of the Moon. Deep Impact and Cassini had also seen the signature, apparently. Faith Vilas had seen it even earlier, from a telescope on Earth, and no one believed her. Remember, however, that this is a different type of water to the chunks or bits of ice everyone imagined at the poles. It would be trace water, H2O molecules in the upper millimeter of soil, that had adsorbed onto minerals.
After the Chandrayaan result came the showtime of LCROSS — a not-so-spectacular crash that yielded a spectacular result: incontrovertible evidence that the impact had tossed up water. Yet more data from LRO and LCROSS were presented at AGU in December.
As a result, the packed-room LRO talks today didn’t surprise me too much, though the data set is getting richer and richer, and making the case for a watery and dynamic moon stronger and stronger. My favorite result came from the LEND instrument on LRO, which counts neutrons as a proxy signature for hydrogen, in turn a proxy for water. Sure enough, LEND, which probes the upper metre of soil, is finding strong evidence for water. But strangely, the hydrogen enrichment isn’t confined to the permanently shadowed regions. In fact, three areas outside of the craters — where they get lots of hot, bright sunlight — showed statistically significant evidence for water.
So what was the press conference all about? I’m not quite sure. Perhaps it was organized to showcase Paul Spudis’ radar work from Chandrayaan, which is about to be published in GRL. Spudis and others have been talking about using radar to detect ice on the moon for years. But other media are taking that as the news of the day.
And in some ways, they are right for paying a little attention to Spudis. If he is right, this will be a third type of ice, much more significant in abundance than the trace amounts of the adsorbed molecules, and the percent or two pore-space bits that LEND and the other LRO instruments are finding. Spudis’ radar would be detecting millions of tons of blocks or chunks of ice in the upper 10 metres – something that would indeed be incredibly useful as a resource if humans ever returned. Ben Bussey, who took over for alleged NASA spy Stu Nozette on a similar instrument on LRO, should have the capability to follow up on Spudis’ work.
Bottom line? The moon is not a dry, dead desert but a wet (well, damp at least) and wild one — with at least a few different types of ice. “There’s not just one flavor of ice on the moon,” said LCROSS’s Tony Colaprete. So let’s stop talking about the discovery of water, and move on to the more interesting questions, which will take months and years to solve: How did the water get there? Is it mostly from the continuous stream of protons emplaced by solar wind? Or do comets and asteroid impacts play a big role? How does the water move around? What percentage of the water is adsorbed molecules? What percentage is ice filling pore space? And what portion of it is the solid chunks that could nourish human exploration?