LCROSS crash coming soon

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Is there water on the Moon, how did it get there and why should we care? The third question is definitely the easiest to answer since if we ever want to build the moon base science fiction has been promising for years, a local water supply will be an essential resource – transporting it from Earth would be both time-consuming and expensive. The second answer is also relatively simple; it’s thought to have accumulated over time from cometary impacts. More information on the first question however will begin to be gathered on Friday when the upper stage of the LCROSS satellite is due to be crashed into the Moon.

The lunar surface is not a very hospitable place for water. Daytime temperatures in the exposed areas can reach up to ~120 degrees Celsius, boiling it off into space. However, ice could survive in the permanently shadowed craters in the polar regions where the Sun’s rays never reach.

Right, now we know where to look for it, finding it should be simple surely? Well yes it would if we wanted to send up some astronauts on a dangerous, costly, mission down into one of these polar craters. A much cheaper option is to send probes and satellites instead.

In 1998 the first tantalizing hints of the presence of lunar ice came from NASA’s Lunar Prospector satellite which detected hydrogen signatures (a possible indicator of water) in polar craters. However, trying to find water from lunar orbit is obviously always going to be harder than finding it from the surface. I’ve already ruled out sending people and a robotic rover (like Spirit and Opportunity on Mars) would also be too inefficient. The simplest and easiest method is to crash a large object into a crater and see what comes out…

This Friday at 4:30 am PDT (12:30 pm in the UK I think) the 2000 kg Centaur upper stage of NASA’s Lunar CRater Observation and Sensing Satellite (LCROSS) will be crashed at 2.5 km/s into the Cabeus crater, the best candidate for finding the signature of water. Four minutes later the remaining part of the spacecraft will then fly through the massive plume of vaporized material thrown up by the impact and analyze what it’s made of. It will then also crash and create a debris plume of its own. Incidentally LCROSS was launched in June along with the Lunar Reconnaissance Orbiter which took the pictures of the Apollo landing sites that Stuart blogged about earlier in the year.

The plume should also be visible from Earth with relatively small telescopes. As a result NASA is encouraging people in America to hold ‘impact parties’ to observe and photograph the crash and then to send them the resulting pictures to help in the data analysis – another example of ‘citizen science’ which I’ve talked about before.

This isn’t the first man-made thing thrown at the moon but I think it’s the biggest so presumably it has the best chance of throwing up enough material to find the water that could be there. It’s just a shame that it’s happening in daytime in the UK so people aren’t going to be able to get their telescopes out and see it here! I’ll be doing the next best thing and watching it live on NASA TV.

(Quick update: you can also watch astronomers observing the impact live at http://mmto.wordpress.com/2009/10/08/watching-lcross-impact/ )