Scientists working with NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) have found the unambiguous signature of water — H2O — on the sunlit surface of the Moon, which can reach scorching temperatures of 120 C (or 250 F).
Making the announcement at a press conference October 26, NASA representatives said the detection occurred at the massive Clavius Crater, which is easily visible through binoculars and telescopes.
NASA’s astrophysics division director Paul Hertz said this is the first time ordinary water molecules have been confirmed outside of the permanently shadowed regions at the poles of the Moon.
“This is exciting, because the expectation is that any water present on a sunlit surface of the Moon would not survive the lunar day,” he said.
Water may be there, but don’t expect to see ponds or streams.
Lead author Casey Honniball — postdoctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland — said that between 100 to 400 parts per million of water molecules were found in this location on the surface of the Moon. That’s not a lot, amounting to about one 12-ounce glass of water per cubic metre of lunar regolith.
“To be clear, this is not puddles of water, but instead water molecules that are so spread apart that they do not form ice or liquid water,” she said. “What’s interesting is that without a thick lunar atmosphere, water on any hot, sunlit surface of the Moon should be lost in space or find its way to the lunar polar cold trap.”
Honniball said researchers think the water is trapped within glass beads in the soil that form during micrometeorite impact.
“These glass beads are about the size of a pencil tip and protect the water from the harsh lunar environment,” she said. “Understanding the source of water and its retention helps piece together the broader history and role water plays in the inner Solar System and on other airless bodies like asteroids, and may have implications for human exploration.”
The discovery suggests a greater distribution of water on the Moon, an environment that astronomers in centuries past thought might have surface water but Apollo-era science suggested was bone dry. Since then, new laboratory techniques have cracked open previously-unstudied Apollo samples and found water molecules. Meanwhile, missions to the Moon over the past three decades found evidence of lunar water ice in permanently shadowed regions of the Moon, clustered around the poles.
Today’s discovery clarifies that ordinary water — not the “drain cleaner” version, hydroxyl — is present on the Moon’s surface during the lunar day.
SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a modified Boeing 747SP carrying a 2.5-metre telescope to make observations in flight, high enough that nearly all the Earth’s water vapor is below the airplane.
Naseem Rangwala, project scientist for the SOFIA mission — which is based in NASA’s Ames Research Center in California — said that SOFIA had never been used for lunar water studies, but that a test in 2018 “far exceeded our expectations.” Researchers found infrared radiation re-emitted at six microns — in other words, a clear signal of ordinary water molecules on the hot, barren lunar surface.
Honniball said the study was “a snapshot of one location at one time on the Moon.” Further flights are planned to increase coverage, potentially yielding a water map of the entire nearside, across all lunar phases.
The international focus on the Moon has quickened with the discovery of lunar water ice in permanently shadows regions of the Earth’s satellite. Hertz said with the Artemis program, NASA aims to land the first woman and next man on the Moon by 2024, and establish a sustainable human presence by the end of the decade.
Christopher Cokinos is co-editor, with Julie Swarstad Johnson, of Beyond Earth’s Edge: The Poetry of Spaceflight, just out from the University of Arizona Press. His astronomical articles, essays and poems have appeared in such venues as Scientific American and the Los Angeles Times. He’s working on a book about the Moon and divides his time between northern Utah and Tucson, with telescopes in each locale.
