No Carbon on the Moon?

 

No Carbon on the Moon?  Not so fast, my friend!

 

We are pretty sure that there is water ice on the Moon, mostly at the poles in Permanently Shadowed Regions (PSRs).  PSRs probably contain water ice and many other volatiles. But some PSRs are colder than others. A recent study published in Nov of 2021 looked at the last 11 years of temperature data from the Diviner Lunar Radiometer Experiment, an instrument aboard NASA’s Lunar Reconnaissance Orbiter. They located the kings of the Cold Traps – cold enough to preserve solid carbon dioxide.

Credit: NASA/GSFC/Arizona State University

The biggest area of concentration looks to be in Amundsen crater (around 82 square km). This does not mean there is necessarily carbon dioxide in the traps, but they are cold enough to preserve it from sublimation. The LCROSS mission detected some carbon dioxide, so if the Moon has appreciable amounts – this is probably where it is hiding.

We’re trying to get rid of excess atmospheric carbon dioxide on Earth but carbon is rare and valuable on the Moon. What can we do with it in situ? We could break it down for oxygen, of course, but there is more than enough oxygen in the regolith. We can use it to make steel, but then there is plenty of aluminum and iron around. Carbon can also be used for biomaterials and it can definitely come in handy in growing food. However, the most valuable use, perhaps in the short term, may be methane. Methane is rocket propellant. Methane is easily obtainable for spacecraft on both Earth and Mars. Now, if it is also available on the Moon…

How hard is it to convert carbon dioxide into methane? Perhaps easier than it used to be. A low-energy method of exposing the carbon dioxide to the lunar day temperatures (around 100 C) in the presence of a catalyst and an electric field could do the trick. The resulting liquid methane could easily be stored in pressure vessels inside PSRs.

If carbon dioxide is harvestable at the South Pole, the Moon could be a valuable methalox propellant station. Note that SpaceX Starship uses methalox for propellant. Of course, hydrogen is also available from breaking down the lunar water ice for propellant.  

The VIPER rover is going to the highlands west of Nobile crater at the South Pole but it is not designed to be able to go down into one of these deep cold traps.  We need an ultra-cold resistant rover (and the infrastructure to support it) to explore Amundsen crater.