NASA has the best evidence yet that there is water on the Moon — and it appears far more abundant and more accessible than scientists first realized.
Trapped in ice, the evidence offers welcome justification for NASA’s ambitious program to not only return humans to the Moon by 2024, but to also establish a long-term, manned lunar base operating on a similar basis to the International Space Station.
As part of NASA's upcoming Artemis mission, the space agency wants to build a permanent lunar base on the Moon that will help astronauts reach further destinations like Mars. However, in order to do that, future astronauts would need to find resources on the Moon that can help accommodate their stay. Chief among them: water.
In a pair of studies published Monday in the journal Nature Astronomy, scientists report both the 'unambigious' detection of molecular water and small, icy water traps that are much more spread out across the lunar surface than previously believed.
In terms of the exact amount of water found, Casey Honniball, one of the scientists who took part in the research and a postdoctoral fellow at NASA, said: "The amount of water is roughly equivalent to a 12 ounce bottle of water within a cubic meter of lunar soil." However it is important to note that the water is seemingly distributed across the lunar surface, and there may be differences across regions, she added. Honniball made the comments during a press conference to announce the discovery Monday.
A watery world — In 2018, scientists discovered evidence of water ice on the Moon's surface, mainly at lunar crater in the Moon's southern pole. Some of the water ice was also apparent at the northern pole, where temperatures never reach above -250 degrees Fahrenheit.
But the new discovery find ice water may be much more abundant across the lunar surface — occupying an area some 40,000 km squared, or about the same area as the country of Switzerland. Importantly, water also appears to exist in areas lit by sunlight — a key distinction from the implication of the 2018 results that water existed only in extremely cold, dark regions on the Moon.
Paul Hayne, a researcher at the Astrophysical & Planetary Sciences Department at the University of Colorado, and lead author of one of the new studies, noticed cold shadows in images of the Moon collected by NASA's Reconnaissance Orbiter and decided to investigate it further.
"If you could keep zooming in forever, at one point would you stop seeing those shadows," Hayne tells Inverse.
By further analyzing the image, the team behind the new study discovered that besides the large permanently shadowed craters on the Moon, there are tens of billions of other smaller cold traps that had not been mapped before across the lunar surface. Some of these are the size of a penny, the data suggest.
"What surprised us is just the sheer number," Hayne says. "Tens of billions of them and spread out throughout the poles."
The new discovery also showed that these shadowed areas can be found within a centimeter of sun-lit areas on the Moon, meaning that they are a lot more accessible than previously believed.Astronauts may not need to venture to the areas of the Moon where temperatures are freezing.
Instead, they could be standing in the relatively warm sunlit areas and still be able to have access to the frozen water.“It definitely expands the possibilities,” Hayne says. “What this discovery does is also expand the real estate on the lunar surface where a base could be viable.”
The studies also find clear evidence that the signs of water the scientists in 2018 found are indeed water, not of hydroxyls. Hydroxyls are used in household chemicals, like drain cleaner, according to Honniball.
Humans' future on the Moon — The scientists behind the two studies reinforced the idea that water is "extremely critical" to deep space exploration. It could be used for drinking water, and for other purposes they said. But water is heavy, Jacob Bleacher, a NASA researcher involved in the work, said during the same conference. That makes it hard to transport from Earth to the Moon, or further into space.
"Finding water that is easier to reach is really important to us," Bleacher said.
Knowing how much water is on the Moon, how it is stored, and whether it is replenished over time are important questions to answer for any future human exploration or stays on the Moon, Bleacher added. Ultimately, scientists hope to establish a lunar water resource map, he said.
SOFIA, NASA's Stratospheric Observatory for Infrared Astronomy, was critical to these new results. But SOFIA was not supposed to study the Moon. It was a shock when, during a test, the scientists operating the observatory found these clear signals of water across the Moon's surface, Naseem Rangwala, project scientist for the SOFIA mission, said during the conference.
An important implication of these results is that when planning a future lunar base, scientists may no longer be restricted to exploring the rims of lunar craters previously known to have ice water. Scientists also noted in the press conference that there is likely similar abundance on the far-side of the Moon as seen here on the near-side.
The discovery offers up new questions about how water can persist on the harsh conditions on the lunar surface, Paul Hertz, Astrophysics division director at NASA, added. The Moon has no atmosphere, and the surface is thought entirely inhospitable due to the harmful affects of solar radiation. But the new results suggest lunar water may withstand solar radiation because it is stored in the form of glass-like beads.
If water can persist — and replenish — across the Moon, then it is possible future lunar explorers could mine and use Moon water as we use water here on Earth, from growing crops to drinking cocktails.
Abstract 1: Widespread hydration was detected on the lunar surface through observations of a characteristic absorption feature at 3 µm by three independent spacecraft1,2,3. Whether the hydration is molecular water (H2O) or other hydroxyl (OH) compounds is unknown and there are no established methods to distinguish the two using the 3 µm band4. However, a fundamental vibration of molecular water produces a spectral signature at 6 µm that is not shared by other hydroxyl compounds5. Here, we present observations of the Moon at 6 µm using the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). Observations reveal a 6 µm emission feature at high lunar latitudes due to the presence of molecular water on the lunar surface. On the basis of the strength of the 6 µm band, we estimate abundances of about 100 to 400 µg g−1 H2O. We find that the distribution of water over the small latitude range is a result of local geology and is probably not a global phenomenon. Lastly, we suggest that a majority of the water we detect must be stored within glasses or in voids between grains sheltered from the harsh lunar environment, allowing the water to remain on the lunar surface.
Abstract 2: Water ice is thought to be trapped in large permanently shadowed regions in the Moon’s polar regions, due to their extremely low temperatures. Here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the areas where ice may accumulate. Using theoretical models and data from the Lunar Reconnaissance Orbiter, we estimate the contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for water ice. Approximately 10–20% of the permanent cold-trap area for water is found to be contained in these micro cold traps, which are the most numerous cold traps on the Moon. Consideration of all spatial scales therefore substantially increases the number of cold traps over previous estimates, for a total area of ~40,000 km2, about 60% of which is in the south. A majority of cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to support ice accumulation. Our results suggest that water trapped at the lunar poles may be more widely distributed and accessible as a resource for future missions than previously thought.