A new study by scientists shows that the surface of the moon holds ice water hiding in the cold, dark places near the north and south poles.
These scientists reported that it appears that this ice — very muddy ice, mixed with a lot of lunar dust — exists inside craters where direct sunlight does not reach it.
The authors of the study, published on Monday in Proceedings of the National Academy of Sciences, say the findings are exciting because they call for further exploration of our rocky satellite.
According to them, the ice could even be a resource for human visitors — perhaps to be used for drinking water, or even to make rocket fuel.
Shuai Li, the lead author and a planetary scientist at the University of Hawaii at Manoa, said that despite decades of lunar research, scientists have had trouble exploring the polar regions, in part because the craters are so dark.
Researchers estimate that the exposed ice covers only 3.5 percent of the craters’ shadowy areas. They don’t know whether the water runs deep, like the tips of buried icebergs, or is as thin as a layer of frost.
The data used by Dr. Li and his team was not new. It had been collected by NASA’s Moon Mineralogy Mapper, which hitched a ride on Chandrayaan 1, India’s first lunar probe, in 2008 and 2009.
The instrument was able to map most of the moon’s surface, but data from the permanent shadows — inside some of the craters near the poles — was a little bit patchy, and hard for researchers to work with.
Dr. Li and his team peered into dark craters using traces of sunlight that had bounced off crater walls.
They analyzed the spectral data to find places where three specific wavelengths of near-infrared light were absorbed, indicating ice water.
They performed rigorous statistical analysis to make sure their results were uncorrupted by coincidental anomalies or instrument errors.
Ralph E. Milliken, a study author and an associate professor in the department of earth, environmental and planetary sciences at Brown University, said he “had a healthy dose of skepticism” when Dr. Li approached him with the idea of sifting through old data to look for clues in infrared. But he soon came around.
“I consider this to be the most convincing evidence that you actually do have true water ice at the uppermost surface — what we call the optical surface of the moon,” he said of the study’s results.
Scientists have researched extraterrestrial water before — on Mercury, for example, or the large asteroid Ceres. But the moon has been difficult.
Radar can be unreliable when the ice water is muddied by sediment, and some spectroscopic analyses couldn’t necessarily distinguish between water and plain old hydrogen.