NASA's intriguing announcement last week that it would reveal an "exciting discovery about the Moon" led to a lot of speculation on what this big discovery might be. We can now all share in the excitement of the space agency: the Moon appears to have a lot of water, and this could make future exploration of our natural satellite much easier.
Two studies published today in Nature Astronomy reveal the important new watery findings. The first paper, led by Dr Casey Honniball from the University of Hawaiʻi at Mānoa, reports the unequivocal discovery of water on the surface of the Moon. The second study, led by Dr Paul Hayne from the University of Colorado, Boulder, examines how the Moon captures and stores this water in "cold traps".
Clues that the Moon hosts water have been collected since the 1970s, but only in the 21st century have researchers been able to find strong evidence. Both NASA’s Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Satellite and India’s Chandrayaan-1 reported the detection of a particular light emission related to water, but couldn’t differentiate between water and other compounds where hydrogen and oxygen are bound together.
Honniball and her team observed the Moon using the Stratospheric Observatory for Infrared Astronomy (SOFIA) airborne telescope, a modified Boeing 747 observatory that flies about 38,000-45,000 feet up in the stratosphere and can view the Solar System in a way ground-based telescopes can't. They were able to detect a specific signature of H2O that is not shared by other compounds. With that, they were able to assess that at high southern latitudes water is present in the soil in about 100 to 400 parts per million, including in a sunlit crater. That’s equivalent to a glass of water for each ton of soil.
The team is unsure where the water is located but posit it could be trapped in glass crystals or remains within the soil grains. It is also uncertain if the water was brought there by asteroids and meteors or is produced on the Moon through a different mechanism.
This is where the second study comes in. Hayne and colleagues looked at the distribution of what is known as "cold traps" on the Moon. These are regions in perennial shadow, where the Sun never shines. The temperature in these shadows remains below 110 kelvins, or -160°C (-260 °F), which means these cold traps are excellent places for ice to form.
"The temperatures are so low in cold traps that ice would behave like a rock," Hayne said in a statement. "If water gets in there, it's not going anywhere for a billion years,"
Their research shows that cold traps ranging from 1 centimeter (0.4 inches) to 1 kilometer (0.6 miles) are likely extremely numerous on the lunar surface. The "micro" traps appear to outnumber the larger ones by hundreds to thousands of times. In fact, they estimate these nooks and crannies that have the capacity to trap water cover about 40,000 square kilometers (15,000 square miles) of the lunar surface, more than double the previous estimate.
Though the traps have been found at both poles, 60 percent of the traps are found above 80 degrees of latitude in the Southern Hemisphere, which confirms this an exciting area to consider for future human exploration.
"If we're right," Hayne said, "water is going to be more accessible for drinking water, for rocket fuel, everything that NASA needs water for."
Whether the water is delivered to the Moon or efficiently produced there, its discovery indeed has important implications for future lunar missions, from establishing a lunar base to providing fuel as a stopover on the way to Mars.
"These results have implications for how humans might extract water to sustain a habitation or make fuel," Associate Professor Alice Gorman from Flinders University, who was not involved in the study, said. "Extraction from small craters might be less technically demanding than mining the big ice craters, but it may also be more destructive to a unique landscape of shadows and ice... As we learn more about the lunar water cycle, it seems that water might be a renewable resource. This is a new challenge for sustainable environment management on the Moon."