Water on the Moon

There has been a lot of planetary science news in the last weeks. I think the most significant is the discovery of water on the moon, detected by NASA’s M³ instrument (Moon Mineralogy Mapper) on the Indian orbiter Chandrayaan-1. These observations were made before Chandrayaan-1 sadly stopped transmitting in late August. The Science papers (abstracts only) can be found here, here, and here.

(image is from the first link, above)

It had long been thought that the impact, melting, and accretionary processes that formed the Moon largely depleted volatiles like water. In 2008, however, water from the Moon’s interior was found in volcanic glass in Apollo 15 and 17 samples, at the level of 100’s of parts-per-million. Some water had been detected before near the lunar poles, and it was suspected that there was ice in the permanently shadowed craters there. Now it looks like water (sensu lato – it’s actually both H₂O and hydroxyl, or OH) is distributed globally in the top few millimeters of the regolith. Most scientists think this surface water is delivered by comets or that it forms by the interaction of the solar wind and cosmic rays with the regolith, but at least one thinks the lunar interior is providing some of it. I suspect comets or solar wind play the bigger role. If we ever go back, and we’re slated to return in the 2020’s, we could investigate the source using stable isotopes or other means.

The presence of this much water in the shallow regolith, as much as 1000 ppm, is important to manned exploration. In my last job, part of my work supported the in situ resource utilization (ISRU) efforts in lunar exploration. Engineers are developing technologies to derive oxygen from lunar regolith to breathe and to use as fuel. It’s much easier to dissociate O from H₂O than to pull it from rocks – in fact, some of the oxygen extraction processes make H₂O, which then has to be dissociated.

I’ve been skeptical, doubtful even, about NASA’s plans to return to the Moon. Between the financial crisis, the new administration (I’m an Obama supporter, but presidents seem to like to change paths when they come into office), and the Augustine Report, things don’t look so good for manned exploration. Personally, I’d like to see humans on the Moon, on Mars and its moons, and on near-Earth asteroids, but I’m more interested in the science than in manned exploration for its own sake. Maybe this discovery of abundant fuel and resources outside of the Earth’s gravity well will be the impetus to get people beyond near Earth orbit again.