Through the looking glass
The first study reports the detection of water molecules on lunar surfaces exposed to the sun, thanks to observations made by the Stratospheric Observatory for Infrared Astronomy (SOFIA) managed by NASA and the German Aerospace Center. It has long been thought that water would have the best chance of remaining stable in regions of the moon, such as large craters, which are permanently covered with shadows. Such regions and any water they contain, the researchers think, will be protected from temperature disturbances induced by the sun’s rays.
When it is discovered, there is water sitting in broad daylight. “This is the first time we can say with certainty that the water molecule is present on the lunar surface,” he says. Casey Honniball, a researcher at NASA Goddard Space Flight Center and lead author of the SOFIA study.
SOFIA observations point to water molecules incorporated into the structure of glass beads, which allows the molecules to withstand exposure to the sun. The amount of water contained in these glass beads is comparable to 12 ounces which are scattered on a cubic meter of earth, scattered on the surface of the moon. “We expect abundance of water to grow as we approach the poles,” Honniball says. “But what we have observed with SOFIA is the opposite” – pearls have been found in a latitudinal region that is closer to the equator, although it is not likely to be a global phenomenon.
SOFIA is an aerial observatory built from a modified 747 that flies high through the atmosphere, so its nine-foot telescope can observe objects in space with minimal disturbance from the Earth’s heavy water atmosphere. This is particularly useful for observing at infrared wavelengths, and in this case it helped the researchers to distinguish molecular water from hydroxyl compounds on the moon.
The characteristics of glassy water on the moon were found in a survey of lunar mineralogy conducted in 1969 (thanks to observations made by a balloon observatory). But these observations have not been reported and published. “Maybe they didn’t realize the great discovery they had made,” Honniball says.
The amount of water contained in the glass grains is a bit low to be useful to humans, but it is possible that the concentration is much higher in other areas (the SOFIA study focused only on one area of the moon). ).
More importantly, the findings raise the possibility of a “lunar water cycle” that could replenish water reserves on the moon, something that seems barely understandable to a world long thought to be dry and dead. “It’s a new area that we haven’t really looked at in great detail before,” he says Clive Neal, a planetary geologist at the University of Notre Dame, who was not involved in any studies.
The second studyHowever, it might be more relevant to NASA’s immediate plans for lunar exploration. The new findings suggest that the moon’s water ice reserves are supported by so-called “micro cold traps” that are only a centimeter or less in diameter. New 3D models generated using infrared and optical images taken by NASA’s Lunar Reconnaissance Orbiter show that the temperatures in these micro traps are low enough to keep the water ice intact. They may be responsible for housing 10 to 20% of the water stored in all the permanent shadows of the moon, for a total area of about 40,000 square kilometers, mostly in regions closer to the poles.
“Instead of just a handful of large cold traps in the ‘named craters,’ there is a whole galaxy of small cold traps scattered throughout the polar region,” he says. Paul Hayne, a planetary scientist at the University of Colorado, Boulder, the lead author of the study. “Micro-cold traps are much more accessible than larger, permanently shaded regions. Rather than devising missions to venture deep into the shadows, astronauts and rovers could stay in the sunlight while extracting water from traps in micro-cold. ”There could be hundreds of millions or even billions of these scattered sites on the lunar surface.
More data makes more mysteries
The studies are not perfect. There is also no clear explanation for how these water-bearing glasses are formed. Honniball says they probably originated from meteorites that either generated water on impact or supplied it as is. Or they may be the result of ancient volcanic activity. Neal points out that the SOFIA study is not able to provide a complete picture of why the distribution of glass appears as a function of latitude, or how it might change for a full lunar cycle. Direct observations are needed to confirm what the two studies suggest, and to answer the questions they pose.
Maybe we shouldn’t wait long for this kind of data. In preparation for Artemis missions to take astronauts to the surface of the moon, NASA plans to launch a robotic mission suites which would also help to characterize the ice water content on the moon. The highest profile of these missions is VIPER, a rover planned for 2022 that is supposed to feature groundwater ice.
In light of the new findings, NASA could choose to slightly change VIPER’s focus to study surface water as well, and take a closer look at all the features of glass or examine how cold micro traps might work. to preserve water ice. Other payloads from NASA, as well missions managed by other countries, are likely to study the surface water content more closely. Neal suggests that a lunar exosphere monitoring system would be very useful for revealing the history of water on the moon and understanding how a possible lunar water cycle results in stable (or unstable) surface water.
“The more we look at the moon, the less we seem to understand it,” Neal says. “Now we have a few more reasons to go back to study. We’re going to come to the surface and get samples and put in place monitoring stations to actually get definitive data to study this type of cycle.”