Scientists have been turning up evidence for the existence of water on the moon for decades, but there’s always been a nagging doubt: Maybe the source of the chemical signatures of hydrogen and oxygen was hydrated minerals, rather than good old H2O.
Now those doubts have been eased, thanks to readings picked up by the Stratospheric Observatory for Infrared Astronomy, also known as SOFIA. The discovery of water’s signature in the moon’s sunlit regions was published today in Nature Astronomy and discussed at a highly anticipated NASA news briefing.
“This new discovery contributes to NASA’s efforts to learn about the moon in support of deep space exploration,” the space agency said.
The readings were gathered two years ago as SOFIA, a heavily modified Boeing 747SP jet, flew above 99% of Earth’s atmosphere — a strategy that made it possible to observe the moon in the right infrared wavelengths.
A research team led by Casey Honniball of NASA’s Goddard Space Flight Center analyzed the spectral characteristics of the infrared light in the 6-micron band, and identified a chemical signature that can be found only in molecular water rather than in hydrated minerals.
They estimate that the concentration of H2O at the surface is about 300 or 400 parts per million at high southern latitudes. Honniball said that’s roughly equivalent to a 12-ounce bottle of water in each cubic meter of surface soil.
In their Nature Astronomy paper, the researchers stressed that the moon doesn’t have water, water everywhere. “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,” they said. But the distribution, at least within the area of Clavius Crater that SOFIA studied, appears to be wider than previously thought.
Scientists have long suspected that water ice might be accumulating in permanently shadowed regions of the moon, but SOFIA’s readings suggest flecks of water could be found within the soil of the moon’s sunlit regions as well.
Based on previous studies of the moon’s surface conditions, the researchers say the water detected by SOFIA almost certainly “resides within the interior of lunar grains, or is trapped between grains shielded from the harsh lunar environment.” They go on to speculate that the water could have been delivered to the moon by meteorite impacts, or liberated from water-bearing minerals by such impacts.
Knowing that honest-to-goodness H2O exists on the moon, at least near the south pole, should boost NASA’s confidence as the space agency proceeds with plans to send astronauts to that region starting as soon as 2024.
Extracting lunar water is seen as a key requirement for supplying lunar operations with drinkable water, breathable air and locally produced energy. Theoretically, H2O can be converted through electrolysis into hydrogen and oxygen, which can in turn power fuel cells and rockets.
It’s an appealing idea for NASA — and also for Amazon CEO Jeff Bezos’ Blue Origin space venture, which is working on a lunar lander that could touch down someday in the moon’s south polar region.
“I think we should build a permanent human settlement on one of the poles of the moon,” Bezos said back in 2017.
However, the newly published findings suggest that extracting the water won’t be as easy as melting down ice cubes.
NASA’s VIPER rover, due for launch to the south lunar polar region in 2023, is designed to find out what it’ll take to get to the moon’s water. (European researchers have their own concept for a rover mission to the moon’s polar regions, known as LUVMI-X.)
Another study published today in Nature Astronomy focused on the sorts of places where lunar water is most likely to persist: those permanently shadowed parts of the polar regions. These are places where the sun doesn’t shine, resulting in temperatures that always stay low enough to keep the water frozen in the ground.
This research team, led by Paul Hayne of the University of Colorado’s Laboratory for Atmospheric and Space Physics, analyzed imagery from NASA’s Lunar Reconnaissance Orbiter to determine just how much of the moon’s surface never sees the sun.
“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,” the researchers write.
Most of the water-bearing areas come in the form of “micro cold traps” — patches of terrain that are less than a yard (a meter) in width. But there are also cold traps that measure more than 6 miles (10 kilometers) in width, particularly in the south polar region.
The cold traps in the south are thought to add up to about 23,000 square kilometers, which covers as much territory as the state of New Jersey. The cold-trapping areas in the north polar region are estimated to total 17,000 square kilometers, which exceeds Connecticut’s area.
Those micro cold traps may sound as if they’re too small to bother with, but Hayne and his colleagues say they might actually be the best places to visit. “If water is found in micro cold traps, the sheer number and topographic accessibility of these locales would facilitate future human and robotic exploration of the moon,” they write.
In addition to Honniball, the authors of “Molecular Water Detected on the Sunlit Moon by SOFIA” include P.G Lucey, S. Li, S. Shenoy, T.M. Orlando, C.A. Hibbitts, D.M. Hurley and W.M. Farrell. In addition to Hayne, the authors of “Micro Cold Traps on the Moon” include O. Aharonson and N. Schörghofer.