What SOFIA’s discovery of water on the Moon is, and isn’t

NASA and the Germany space agency’s airborne SOFIA telescope has detected water on the Moon’s surface. There are many misconceptions floating around this discovery so I’d like to clarify the nature of the findings and what it means for lunar science and exploration.

This illustration highlights the Moon’s Clavius crater with an illustration depicting water trapped in its lunar soil, along with an image of NASA’s airborne SOFIA telescope that found such water. Credits: NASA/Daniel Rutter

Different from Chandrayaan 1

SOFIA detected water on the Moon’s non-polar regions, and in areas of sunlight, making it different from ISRO Chandrayaan 1’s discovery of water ice inside dark, cold craters on the lunar poles.

The water SOFIA found is locked in the lunar soil and rocks. Interestingly, NASA’s M3 instrument on Chandrayaan 1 had seen hints of such trapped water in non-polar regions, as did Cassini. But unlike SOFIA, those missions couldn’t tell if what they had detected was water or just hydroxyl groups (H2O vs OH).

Chandrayaan 1 dropped an impact probe on the Moon 12 years ago and did find water, as in H2O. But it too is different from SOFIA’s findings because the probe detected water in the Moon’s thin atmosphere, not on the surface.

Scientific, not exploratory importance

NASA PR spinned the announcement as the water being a promising source for future missions in creating sustainable habitats. But that’s not the case since this trapped water is in trace amounts, less than even the driest deserts on Earth. However, finding out where this water comes from or how it’s created has implications for understanding the Moon’s origin, which itself is tied to Earth’s.

The one area where the results have some exploratory relevance is understanding how water is transported on the Moon, so as to get a better handle on where on the Moon such resources are deposited. But the substantially more water ice present on the lunar poles continue to be the prime target for enabling sustainable human presence on the Moon.

Illustration showing water ice in eternally dark craters on the Moon’s south pole (left) and north pole (right) as discovered by ISRO’s Chandrayaan 1 spacecraft. Credit: NASA

Alongside the SOFIA findings, NASA mentioned another result that does have exploratory significance. Researchers using data from NASA’s Lunar Reconnaissance Orbiter have identified several craters smaller than a kilometer which are eternally dark and can thus can host water ice. The sheer number of such small craters increases the expected amount of water ice on the Moon.

As per previous observations by the Chandrayaan 1 orbiter and the Lunar Reconnaissance Orbiter, scientists estimated the Moon’s poles to host more than 600 billion kilograms of water ice, enough to fill at least 240,000 Olympic-sized swimming pools. As the next logical step, Chandrayaan 2 orbiter is quantifying the amount of water ice on the lunar poles and mapping it as we speak, and its findings should include these smaller craters.

Once we have such data, these smaller, dark craters will likely be better targets for future missions as they’d be easier to explore and extract water from than large craters like Shackleton.

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