Source: Sci News

Up until the last decade, planetary scientists thought the Moon was arid, with any water existing mainly as pockets of ice in permanently shaded craters near the lunar poles.

More recently, they have identified surface water in sparse populations of molecules bound to the lunar soil (regolith). The amount and locations vary based on the time of day. This water is more common at higher latitudes and tends to hop around as the surface heats up.

Water molecules remain tightly bound to the regolith until surface temperatures peak near lunar noon. Then, they thermally desorb and can bounce to a nearby location that is cold enough for the molecule to stick or populate the Moon’s exosphere, until temperatures drop and the molecules return to the surface.

“Lunar hydration is tricky to measure from orbit, due to the complex way that light reflects off of the lunar surface,” said study co-author Dr. Michael Poston, a research scientist at Southwest Research Institute.

“Previous research reported quantities of hopping water molecules that were too large to explain with known physical processes. I’m excited about these latest results because the amount of water interpreted here is consistent with what lab measurements indicate is possible.”

Researchers have hypothesized that hydrogen ions in the solar wind may be the source of most of the Moon’s surface water.

With that in mind, when the Moon passes behind the Earth and is shielded from the solar wind, the ‘water spigot’ should essentially turn off.

However, the water observed by the LAMP instrument does not decrease when the Moon is shielded by the Earth and the region influenced by its magnetic field, suggesting water builds up over time, rather than ‘raining’ down directly from the solar wind.

“These are important new results about lunar water, a hot topic as our nation’s space program returns to a focus on lunar exploration,” said LAMP principal investigator Dr. Kurt Retherford, also from Southwest Research Institute.

“Our results aid in understanding the lunar water cycle and will ultimately help us learn about accessibility of water that can be used by humans in future missions to the Moon,” said Dr. Amanda Hendrix, a senior scientist at the Planetary Science Institute.

“Lunar water can potentially be used by humans to make fuel or to use for radiation shielding or thermal management; if these materials do not need to be launched from Earth, that makes these future missions more affordable.”

The study was published in the journal Geophysical Research Letters.