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.
Rachel L. P. Klima, a senior staff scientist at the Johns Hopkins University Applied Physics Laboratory who was not involved with the study, said Dr. Li’s results were impressive.
“We’ve had all of these kind of circumstantial things that hinted at ice on the moon — different data sets — but there really was not a robust observation that could only be attributed to ice,” she said. “This is, in my opinion, the first evidence that there’s really no other way to explain.”
Dr. Li hopes to see more lunar exploration in the near future. In fact, this new evidence of ice could make such exploration more likely. After all, scientists still have questions about how deep this water goes, whether it could be useful to human visitors, and where it came from — was it delivered by comets and asteroids? And if so, when?
The use of near-infrared light could help scientists find new answers to those questions.
“We’re really pushing the boundaries,” Dr. Milliken said of the study methodology. “I could imagine, now that we know this does work, you could easily go and design an instrument that is tailored to these more difficult conditions and that would open even more doors.”
