A new study led by NASA scientists has discovered water present on the moon's surface in places previously thought to be impossible, raising new potential for harvesting the valuable resource on manned lunar missions later this decade.
The study published this week found water on sunlit parts of the moon's surface, refuting a long-standing theory that water could not survive the lunar day. It opens up the possibility that water could be easier to harvest and more plentiful, giving future missions to the moon the possibility of accessing water from areas other than the ice packed on the moon's dark and frigid poles.
The landmark study now has NASA scientists theorizing how exactly water can persist across the moon's surface and how much of it is present. It's also unclear to what extent humans could access the water to drink, turn it into oxygen or tap into as a fuel supply.
"This discovery raises new questions about how water is created and how it can persist in the harsh, airless conditions of the sunlit lunar surface," said Paul Hertz, NASA's Astrophysics Division director, at a press conference Monday.
Scientists have known for years about the presence of hydrogen on sunlit parts of the moon, but the measurements were too imprecise to determine whether it was water or hydroxyl, a similar molecule, said Casey Honniball, the lead author of the study. But researchers were able to use a powerful infrared telescope known as SOFIA, or Stratospheric Observatory for Infrared Astronomy, to observe the moon's surface at just the right wavelength to check for a chemical fingerprint unique to water.
"This observation finally allowed us to definitely determine that water molecules are present on the sunlit surface of the moon," Honniball said.
The study focuses on SOFIA's observations in the southern hemisphere of the moon's surface at and around the Clavius crater, a huge impact crater more than 140 miles across. Water was measured at a concentration of between 100 and 400 parts per million -- hardly puddles of water, Honniball said, but enough to fill a 12-ounce bottle of water from a cubic meter of powdery lunar soil.
The observations are limited in the sense that it can only detect water on the very surface of the moon, and it's unknown whether water could be buried meters underground.
SOFIA is a heavily modified 747 jet outfitted with a powerful infrared telescope designed to take measurements from high in the earth's atmosphere, flying up to 45,000 feet above ground to make accurate measurements above 99.9% of the water vapor in Earth's atmosphere, said Naseem Rangwala, project scientist for the SOFIA mission at NASA Ames Research Center in Mountain View. The observations that became the basis for the significant discovery were originally just a test, she said, checking out the moon's surface while flying over Nevada en route back to California in 2018. The instruments onboard were used to pick up a specific wavelength unique to water molecules at 6.1 micrometers.
"SOFIA is currently the only telescope on or off this world that can provide remote access to this unique chemical fingerprint," Rangwala said.
So how does water survive on the hot, sunlit surface without a thick lunar atmosphere? Scientists believe those conditions meant water would either be lost to space or end up in the polar "cold trap" with temperatures low enough to keep water condensed. The current theory, Honniball said, is that water is trapped and preserved in tiny glass beads, likely formed when micrometeorites strike the moon's surface. It's possible that solar winds deliver hydrogen that reacts with oxygen present on the moon, or it could be that the meteorites were carrying water during the crash landing, she said.
"These glass beads are about the size of a pencil tip and protect the water from the harsh lunar environment," Honniball said.
NASA is currently pushing to send a crewed mission to the surface of the moon by 2024 as part of the Artemis program, which is largely focused on "sustainable" exploration of the lunar surface. It's also seen as a stepping stone to better prepare for the first manned mission to Mars. Jacob Bleacher, NASA's chief exploration scientist, said the discovery could have huge implications, as water is heavy and expensive to launch from Earth and will eventually run out.
Up until now, Bleacher said the expectation was that astronauts would have to harvest water from cold, dark environments that are difficult to reach and even harder to work in for extended periods of time. As part of the Artemis program, NASA scientists have been working on lunar rovers capable of drilling one meter below the surface to look for and sample water ice on the poles.
The possibility of more plentiful and easy-to-access surface water could be a game changer and ease the dependence on polar ice, but Bleacher said many questions need to be answered. If water is locked into glass beads, it could require more energy to extract than if it were simply mixed in with the soil. It's unclear how the water gets on the surface, how much of it exists, whether it moves around and if it replenishes over time, he said.