Surprise! Water Found On Moon's Surface
Three different space probes have gathered evidence that the top layer of the moon's surface contains hidden stores of water.
The moon is generally thought to be a dry place, although scientists have long suspected that ice might be trapped in cold, permanently shadowed craters. A NASA mission will test that theory next month, by smashing a spent rocket part into a dark crater near the moon's south pole and creating a big debris cloud that will be searched for water.
But surprisingly, researchers have now found that there's water on the sunlit surface of the moon, where no one expected it to be.
Molecules of water as well as hydroxyl — that's just one atom of hydrogen with an oxygen atom, instead of the two hydrogen atoms normally found in water — are all over the lunar surface, in the very top layer of dust, according to new reports published online by the journal Science.
The first hint that the water might be there came from a NASA instrument called the Moon Mineralogy Mapper on board the Chandrayaan-1 spacecraft launched by India last October to orbit the moon.
A Shock To Researchers
The discovery was so surprising that researchers at first thought it was some kind of calibration problem. "Like any normal person, you'd say, 'Well, that's ridiculous, you know. It can't be there,' " says Carle Pieters, a planetary geologist at Brown University.
"So we spent months on the team, scrubbing this data with every means possible, arguing amongst ourselves," Pieters says, "and it would not go away."
Then they were able to confirm their observations using data from two additional spacecraft: NASA's Cassini probe that passed by the moon in 1999 while traveling to Saturn, and the Deep Impact spacecraft, which whizzed by the moon in June of this year on its way to visit a comet.
The water seems to be a very thin film of molecules stuck to the surface, says Jessica Sunshine of the University of Maryland-College Park.
"It's not liquid water, it's not frozen water and it's not gaseous water, OK? It's none of those things," Sunshine says. "It's not your grandmother's water on the moon. It's a completely different mindset. You sort of have to throw out everything you think of by that phrase."
Pieters concurs that the moon is still a very dry place. "There's no question about that. The amount of water is small," she says, even though it is found extensively over the moon's surface.
Still, the discovery has excited space buffs who say water and hydroxyl could be an important resource if astronauts ever return to the moon. NASA has spent the past few years working toward a return by 2020, and has even talked of plans for a lunar base, but that program is currently under review by the Obama administration.
A Previously Unknown Process
Sunshine estimates that scraping off all the water molecules from a part of the lunar surface the size of a football field would yield less than a quart of water. "And it could be a lot less. I think our understanding is not great," she says. "You're certainly not going to turn around and shovel up a bit of lunar regolith and start drinking it," she says, referring to the dusty lunar dirt.
The water seems to appear and disappear during the course of the lunar day, as temperatures rise and fall.
Scientists still aren't sure what the source of the water is, although they suspect that hydrogen atoms in the solar wind might be hitting lunar minerals and reacting with the oxygen in them.
But they say it was amazing to find such a dynamic and completely unknown process occurring on the moon. "Nature surprises us, and in this case, the moon completely surprised us," Pieters says. "This is something we were not expecting."
When the Apollo astronauts brought back samples from the moon, those specimens did contain trace amounts of water, but it was assumed to be water from Earth that had gotten mixed in by accident.
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MADELEINE BRAND, host:
Scientists have made a surprise discovery about our moon. It is generally thought to be bone dry but now, three new studies show that actually, the lunar dirt holds stores of hidden water.
NPR's Nell Greenfieldboyce reports.
NELL GREENFIELDBOYCE: Nobody thought the surface of the moon was covered with water. Even the scientist who saw the first hints of water didn't believe it.
Professor CARLE PIETERS (Geological Sciences, Brown University): Like any normal person, you'd say, well, that's ridiculous. You know, it can't be there. It must be calibration problems.
GREENFIELDBOYCE: Carle Pieters says her team thought their instrument must be out of whack. They spent months looking at their data.
Prof. PIETERS: Arguing amongst ourselves what could be real, what could not be real - and it would not go away.
GREENFIELDBOYCE: Pieters works at Brown University. She heads up research with a NASA instrument called the moon mineralogy mapper, which went up on a space craft built by India to orbit the moon. To make sure this mapper really had picked up water, the scientists got data from two other spacecrafts that flew by the moon. It turns out those probes detected signs of water, too. But Pieters says it's not the kind of water we normally think about here on Earth.
Prof. PIETERS: There's no oceans. There's no clouds. There's no lakes. There's no puddles. This is completely different.
Ms. JESSICA SUNSHINE (Senior Research Scientist, University of Maryland): You know, it's not your grandmother's water on the moon.
(Soundbite of laughter)
Ms. SUNSHINE: It isn't. You sort of have to throw out everything you think of by that phrase.
GREENFIELDBOYCE: Jessica Sunshine is a researcher at the University of Maryland in College Park.
Ms. SUNSHINE: It's not liquid water.
(Soundbite of laughter)
Ms. SUNSHINE: It's not frozen water and it's not gaseous water. OK? It's none of those things. What it is is a very thin film, maybe several layers of molecules thick.
GREENFIELDBOYCE: She says if you could scrape all the water molecules off an area about the size of a football field, you'd get maybe a quart.
Ms. SUNSHINE: And it could be a lot less. I think our understanding is not great.
GREENFIELDBOYCE: Another thing that's not yet understood is the source of the water. It seems to come and go over the course of the lunar day, as temperatures change. The new findings are being published this week by the journal Science. Carle Pieters says it was amazing to discover a previously unknown, dynamic process on our nearest celestial neighbor.
Prof. PIETERS: Nature surprises us. And in this case, the moon completely surprised us. This was something that we were not expecting.
GREENFIELDBOYCE: One reason space enthusiasts are so interested in water on the moon is because of hopes that it could come in handy if astronauts ever go back. NASA has been working on new rockets and space capsules for a return by 2020. There's even talk of a lunar base. Those plans are all currently under review by the Obama administration. And at a press conference this afternoon, experts pointed out that the moon's surface still looks pretty dry despite these new findings. Jim Green is director of NASA's planetary science division.
Dr. JIM GREEN (Director, Planetary Science Division, NASA): Even the driest deserts in the Earth have more water than are at the poles and the surfaces as we've presented here on the moon.
GREENFIELDBOYCE: Still, NASA hopes to find more water next month. Scientists had long assumed if the moon had any water at all, it would be frozen at the bottom of dark, cold craters. So in October, NASA will put a spent rocket part on a collision course with that kind of crater to see if the impact kicks up evidence of buried ice.
Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright National Public Radio.
