Glass Beads From Moon Hint Of Watery Past
Scientists have found water in some tiny beads of volcanic glass that Apollo astronauts collected on the moon decades ago, raising new questions about how the moon was born.
For a long time, scientists have thought "that the moon is completely dry," says Erik Hauri, a geochemist at the Carnegie Institution's Department of Terrestrial Magnetism in Washington, D.C.
They believed there couldn't be water on the moon because of how it was formed. According to the "giant impact" theory, the moon was born 4.5 billion years ago when an object the size of Mars came hurtling out of the void and smacked the young Earth.
This impact melted both objects and scattered a cloud of debris around the Earth. That debris became the moon — and the new moon was a hot ocean of magma.
Researchers thought there was no way a moon this hot could have retained any water.
But Hauri got together with some colleagues to look for water in a special kind of material collected on the moon by Apollo astronauts: tiny bits of glass created by volcanic eruptions on the early moon.
"They're very tiny, the size of a period on a typical printed page," says Hauri, who explains that as volcanoes on the moon erupted, tiny droplets cooled in the air, turning to glass before they even hit the ground.
The glass beads come in different colors. Some were almost invisible and had to be picked out of gray moon dust, but others could be seen by the astronauts as they walked around on the lunar surface.
Moonwalker and geologist Harrison Schmitt discovered some of them back in 1972, during the Apollo 17 mission, when he looked down and was shocked to discover orange soil at his feet.
A study about 10 years ago looked at the beads and saw hints of water. But the results also fell within the instrument's margin of error. So Hauri and his colleagues decided to look again using newer, more sensitive detection technology.
Some moon experts were skeptical, saying there was no way the team would find any water molecules. "We got a lot of comments like, 'Oh, well, we already know that the moon is dry, we've known this for 20 years,'" Hauri says.
But this time they did find water molecules, according to a report in the journal Nature.
It wasn't a lot of water. The beads had only up to 46 parts per million. But from this, the researchers estimate that the interior of the moon once probably contained an amount of water equal to that of the Caribbean Sea.
This is a problem for the giant impact theory, says Hauri. "It's hard to imagine a scenario in which a giant impact melts, completely, the moon, and at the same time allows it to hold onto its water," he says. "That's a really, really difficult knot to untie."
Others agree that the discovery raises questions. "It's obviously a very new result to say that the moon might have had a significant amount of water right after it formed," says Ben Bussey, with the Johns Hopkins University Applied Physics Lab in Laurel, Md.
Scientists have seen hints of ice at the moon's poles, in cold, shadowed craters. But because the moon was assumed to be dry, researchers thought this ice had to come from meteorite impacts.
Now there's a small but real possibility that some of that ice — if it exists — may have come from inside the moon. "There is a chance that there might be some very old water of the type that they discuss in the paper," Bussey says.
If the moon does have ice, Bussey says, scientists could figure out where it came from, but only if a rover or an astronaut goes to get a sample.
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MICHELE NORRIS, Host:
At night, the moon can appear white or yellow or even red, but astronauts who walked on the moon mostly saw shades of grey. Once, though, a couple of astronauts saw something that amazed them: some brightly colored dirt.
Now, decades later, scientists have found a surprise inside that dirt which may teach us something new about the birth of the moon. NPR's Nell Greenfieldboyce reports.
NELL GREENFIELDBOYCE: Back in 1972, Harrison Schmitt was walking on the moon when he suddenly saw something shocking. It was a color.
HARRISON SCHMITT: It's all over. (Unintelligible)
GREENFIELDBOYCE: Schmitt and his fellow moonwalker, Eugene Cernan, could hardly believe it.
EUGENE CERNAN: It is. I can see it from here. It's orange. It's crazy.
GREENFIELDBOYCE: The astronauts scooped some up. Back on earth, scientists realized that the orange color came from bits of glass.
ERIK HAURI: They're very tiny, the size of a period on a typical printed page.
Erik Hauri is a geochemist. He says volcanoes made the glass a few billion years ago, when the moon was young.
HAURI: And these glasses are circular or spherical beads that form when the lava is ejected at high velocity out of the erupting crater and cools so quickly that it quenches to a glass in the air before it falls back to the surface.
GREENFIELDBOYCE: The glass beads come in different colors. They've been analyzed before, but Hauri and his colleagues wanted to take a fresh look to see if the beads contained any water. Some moon experts thought there was no way they'd find any.
HAURI: We got a lot a lot of comments like, oh, well, we already know that the moon is dry, you know, we've known this for 20 years,.
GREENFIELDBOYCE: People thought the moon was dry because of how it formed.
HAURI: Through a process called giant impact.
GREENFIELDBOYCE: Scientists believe the moon was born 4.5 billion years ago, when an object the size of Mars came hurtling out of the void and smacked the young Earth. This melted both objects and put a cloud of debris around the Earth. That became the moon. The new moon was hot, like a sea of magma.
HAURI: The prevailing idea has been that there's no way a completely molten moon could have retained any water.
GREENFIELDBOYCE: But Hauri thought, well, let's just see. He has an instrument in his lab at the Carnegie Institution of Washington that's very sensitive. He blasted molecules off the glass beads and found that some of those molecules were water molecules. According to a report in the journal Nature, it wasn't a lot of water, less than 50 parts per million, but from this, the researchers can estimate that way back when, the interior of the moon probably contained as much water as the Caribbean Sea. Hauri says this is a problem for the giant impact theory.
HAURI: It's really hard to imagine a scenario in which a giant impact melts completely the moon, and at the same time allows it to hold onto its water, and that's a really, really difficult knot to untie.
BEN BUSSEY: It's obviously a very new result to say that the moon might have had a significant amount of water right after it formed.
GREENFIELDBOYCE: Ben Bussey is a planetary scientist at the Johns Hopkins University Applied Physics Lab. He says besides raising questions about the giant impact theory, the finding raises another question too. Scientists have seen hints of ice at the moon's poles, in cold, shadowed craters. Everyone has thought this ice had to come from outside the moon, probably from meteorite impacts, but maybe some of it came from inside the moon.
BUSSEY: There is a chance that there might be some very old water of the type that they discuss in the paper.
GREENFIELDBOYCE: If the moon does have ice, he says scientists could figure out where it came from, but only if a rover or an astronaut went to get a sample. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright National Public Radio.
