Make a note: if you ever find yourself exploring the moon one day and you want to try some lunar skinny-dipping, you’ll have to do it at night.
All right, so there’s no water-filled lakes on the moon (and you’d be strongly advised to keep your suit on). But there is surface water, both in the form of ice inside polar craters and as scattered molecules within lunar soil and rocks. Except when the sun hits them — that is, ultraviolet radiation in the sun’s light — water molecules on the moon’s surface are set free and potentially even broken apart, as described in recent findings by researchers from Georgia Tech.
“If a lot of sunlight is hitting me, the probability of me getting sunburned is pretty high,” describes Thomas Orlando, professor and associate director of the Center for Space Technology and Research at Georgia Tech. “It’s similar on the moon. There’s a fixed solar flux of energetic photons that hit the sunlit surface, and there’s a pretty good probability they remove water or damage the molecules.“
A full solar day on the moon lasts about 29.5 Earth days, so any particular location will be receiving sunlight for a little over 14.5 days. During that long lunar daytime the sun’s harsh UV radiation, combined with the thermal heating of the moon’s surface, will apparently release — or “desorb” — molecules of H2O, scattering them into the thin lunar exosphere.
The research was performed using actual lunar samples and a high-powered vacuum system that recreates the conditions in space. By firing UV rays at the sample, scientists were able to observe what happened to the water molecules.
The desorption doesn’t occur with enough energy to send the individual molecules flying off the moon completely though; after the sun “sets” and the lunar surface cools, they could be redeposited elsewhere — perhaps even along some of the permanently-shadowed walls of craters at the moon’s poles. (That is if the molecules don’t end up breaking apart entirely en route.)
We’re not talking about high concentrations of water here, but over time — that is, tens or even hundreds of millions of years — this lunar version of a water cycle would build up.
While these findings mean that water won’t likely be found in any usable amounts on our moon’s sunny side, they can help scientists know where to look for it on other worlds, both in our own solar system and beyond.
Source: Georgia Institute of Technology