The search for water on the moon has produced a discovery of tiny molecule-sized perhaps widespread amounts of H20 in a sunlit lunar crater.
The water is not in a liquid or ice or gaseous form, but rather apparently contained (and protected) inside glass beads formed when micrometeorites hit the surface.
The detection was made using the Stratospheric Observatory for Infrared Astronomy (SOFIA), a high-flying modified airplane with an infrared telescope.
NASA scientists made clear that the lunar H2O in sunlight might prove to be too difficult to collect to be of use to astronauts, but future robotic and human missions on the lunar surface could also find more concentrated deposits now that they know some water is present.
“Prior to the SOFIA observations, we knew there was some kind of hydration” on the lunar surface said Casey Honniball, the lead author of a paper in the journal Nature Astronomy. “But we didn’t know how much, if any, was actually water molecules – like we drink every day – or something more like drain cleaner.”
“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Honniball, who is now a postdoctoral fellow at NASA’s Goddard Space Flight Center. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”
Scientists have searched for water on the moon since Apollo days, and have known for some time that frozen water exists in some always-dark craters of the lunar south pole. Prior lunar missions have also detected hydrogen on sunlit surfaces, and it was initially thought to be in the form of hydroxyl (OH) rather then water (H2O.)
SOFIA offered a new means of looking at the moon. Flying at altitudes of up to 45,000 feet, this modified Boeing 747SP jetliner with a 106-inch diameter telescope reaches above 99% of the water vapor in Earth’s atmosphere to get a clearer view of the infrared universe.
Using its Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), SOFIA was able to pick up the specific wavelength unique to water molecules, at 6.1 microns, and discovered a relatively surprising concentration in sunny Clavius Crater.
Honniball suspects the water is produced when in-coming micrometeorites or solar winds interact with the lunar soil and in the process modify the hydroxyl into water, or deliver H2O already in a micrometeorite. The H2O is then protected in pockets between grains of moon dust or within bead-like glass formed by the heat produced during micrometeorite impacts.
“The water must be sheltered from the harsh lunar environment, because at the time of our observations the location on the moon was quite warm,” Honniball said.
The SOFIA study detected individual molecules of water near the Clavius crater, in the moon’s southern region. Because the water molecules are so spread out, Honniball said, they don’t “interact with one another and so cannot form liquid water or water ice.”
So the concentation of surface water is small for sure — NASA described the lunar water concentration detected by SOFIA to be 1/100th of what would be found in the Sahara desert. But this discovery may be just the start. Although the molecules of water found in this new study aren’t abundant enough for astronauts to use — and surely aren’t potable — Honniball said greater concentrations may be found in other regions of the moon, underground, and especially in ancient volcanic deposits.
As a result, the findings raise welcome if complicating questions for the NASA personnel in charge of the Artemis mission — which hopes to land astronauts on the moon in the mid 2020s and to begin establishing a self-sustaining astronaut colony on the moon in the 2030s.
And so during the NASA press conference about the lunar water discovery, members of the NASA human exploration team had a lot to say.
Since water is heavy to transport from Earth to the moon, any long-term presence on the moon requires a lunar source of H2O.
Before this Clavius Crater discovery, the only water known for sure to be present on the moon was locked as ice in those always dark craters of the poles. These deposits may be large, especially near the southern pole, but the water would be very difficult to collect for drinking or to crack to produce oxygen for breathing and hydrogen for fuel.
“Water is a valuable resource, for both scientific purposes and for use by our explorers,” said Jacob Bleacher, chief exploration scientist for NASA’s Human Exploration and Operations Mission Directorate. “If we can use the resources at the moon, then we can carry less water and more equipment to help enable new scientific discoveries.”
Bleacher said numerous smaller missions will be headed to the moon in the years ahead to, in effect, prospect for water and to see what sources might be most accessible.
Included are SOFIA’s follow-up flights that will look for water in additional sunlit locations and during different lunar phases to learn more about how the water is produced and stored. The data will add to the work of future moon missions, such as NASA’s Volatiles Investigating Polar Exploration Rover (VIPER), to create the first water resource maps of the moon for future human space exploration.
The additional robotic missions will also study whether or not the water beads move, if they are stable, and whether they will change with the approach of a machine. Some will bring a drill for digging.
In the same issue of Nature Astronomy, scientists have published a paper using theoretical models and NASA’s Lunar Reconnaissance Orbiter data that suggest other venues for water ice. They hypothesize that water could be trapped in small shadows where temperatures stay below freezing that can be found across more of the moon than currently expected . The results can be found here.
SOFIA is a joint NASA and German Aerospace Center mission designed to look at distant, dim objects such as black holes, star clusters, and galaxies. So its use for lunar science was a departure from business as usual.
The telescope operators typically use a guide camera to track stars, keeping the telescope locked steadily on its observing target. But the moon is so close and bright that it fills the guide camera’s entire field of view. With no stars visible, it was unclear if the telescope could reliably track the moon. To determine this, in August 2018, the operators decided to try the test observation that proved to be so productive.
“It was, in fact, the first time SOFIA has looked at the moon, and we weren’t even completely sure if we would get reliable data, but questions about the moon’s water compelled us to try,” said Naseem Rangwala, SOFIA’s project scientist at NASA’s Ames Research Center. “It’s incredible that this discovery came out of what was essentially a test, and now that we know we can do this, we’re planning more flights to do more observations.”
While it was unclear whether SOFIA could actually observe the moon, it was not a surprise that it could detect chemicals — it specializes in assessing star chemistry.
When visible light is spread into its component colors, a rainbow appears. But when infrared light is broken into its components, it reveals a series of bright lines, called spectra. Each element creates a unique line, so the lines act as chemical fingerprints. Scientists use them to identify which substances are in and around stars. SOFIA’s instruments can detect small details in the chemical fingerprints from the cores of massive young stars, similar to how high-resolution images reveal tiny features.
In a recent Astrophysical Journal article, authors described SOFIA observations of massive young stars where future planets could begin to form.
It found massive quantities of organic molecules in these swirling, disk-shaped clouds, offering new insights into how some of the key ingredients of life get incorporated into planets during the earliest stages of formation. These carbon-based organics are the basis of life on Earth, have been found on Mars and in the plumes of the moon Enceladus, in meteorites and comets, and in the interstellar dust.
In addition to the organics, SOFIA also found in those distant stellar clouds large amounts of H2O.
Many Worlds 