In early October, NASA’s LCROSS mission will impact a crater near the Moon’s south pole, creating a massive plume of debris that will be visible from Earth. Telescopes on the ground, and on board the LCROSS shepherd spacecraft, will search this plume for evidence of water vapour.
The main goal of this mission is to provide evidence of ice deposits in the Moon’s polar regions, which are believed to lie in permanently shadowed craters.
Finding water on the Moon is scientifically interesting and highly practical. The water deposits could support astronauts living on a Moon base in the future.
Although the search for water is clearly the most important objective of the LCROSS mission, there will probably be other discoveries. This author would like to predict a potential discovery that hasn’t received a lot of media coverage: argon gas.
Argon is a noble gas that gives a nice blue glow to some fluorescent light tubes. We know it’s on the Moon. Rock samples from the Apollo missions held traces of argon, which is produced by the decay of radioactive rocks.
There’s no reason why argon shouldn’t be at the poles, but there is reason to suggest that there could be more of it there than elsewhere. The polar regions are very cold, as NASA’s Lunar Reconnaissance Orbiter recently discovered. In fact, the poles could be the coldest places in our solar system!
Temperatures are so low that argon would be frozen solid. This could help these regions to retain more argon than the hotter regions of the Moon, because argon gas escaping from rocks over a long period could simply freeze in place. Admittedly, radioactive decay produces heat as well as trace gases, but the gas could percolate upwards from hot, underground areas and reach the colder surface.
The low temperatures recently observed at the poles suggest that there’s not much heat from radioactive decay there today, but the argon could have been held in a frozen state for eons.
Alternatively, argon released from other regions of the Moon could migrate to the poles as a cold trap.
There are likely to be other volatiles at the poles, but I suspect that no other noble gases will be found in higher quantities. Some are too volatile to be frozen as clumps of ice, or don’t seem to be present in high quantities in the Apollo samples. There could be some helium there, but not as much as other parts of the Moon.
We won’t have long to wait before this theory is tested.