Moon's Changing Water Ice Explained by Galactic Cosmic Rays

On the far reaches of Earth's moon, ice is locked in one of the solar system's coldest regions. Now, scientists have explained how galactic cosmic rays penetrating lunar soil can actually create molecular hydrogen from water ice, which provides insight into how radiation can change the chemistry of ice throughout the solar system.

Finding molecular hydrogen on the moon was surprising. Discovered after NASA's Lunar Crater Observation Sensing Satellite (LCROSS) sent its spent Centaur rocket crash-landing into the Cabeus crater at 5,600 miles per hour, the hydrogen was a component in the giant debris plume that was blasted into the atmosphere from the crash. 

Finding the hydrogen was a surprise, though. While the scientists expected to see water vapor and water ice, they hadn't planned on seeing hydrogen. After it was detected, though, researchers began trying to figure out why it was present beneath the lunar soil. More specifically, they examined data gathered by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument aboard the LRO spacecraft. 

"After the finding, there was a couple of ideas for how molecular hydrogen could be formed but none of them seemed to work for the conditions in the crater or with the rocket impact," said Andrew Jordan of the University of New Hampshire's Institute for the Study of Earth, Oceans and Space, in a news release. "Our analysis shows that the galactic cosmic rays, which are charge particles energetic enough to penetrate below the lunar surface, can dissociate the water, H2O and H2 through various potential pathways."

Molecular hydrogen is formed when water (H2O) breaks apart into its components. Essentially, the scientists found that high-energy particles, which can originate from supernovae, penetrate the moon's atmosphere and, consequently, the lunar surface. These particles spark a reaction in the buried ice that forms the molecular hydrogen. In fact, the scientists found that these particles can form between 10 and 100 percent of the H2 measured thus far.

The study reveals a little bit more about the processes that go on beneath the lunar surface. It may show us a little bit more about how radiation can change the chemistry of water in our solar system.

The findings are published in the Journal of Geophysical Research: Planets.