Saal Lab/Brown University
It's long been accepted that the moon is dry. No oceans wash its Swiss cheese surface, and lunar rocks and soil samples collected by Apollo astronauts 40 years ago bolstered the case the moon was an arid place.
But a paper published today challenges that notion -- and the findings emerged from a summer research project that Westwood native Thomas Weinreich worked on after his freshman year at Brown University, when he painstakingly sorted through thousands of grains of moon dust.
Weinreich wasn't strictly following orders. He had been asked to pick out orange glass beads from lunar soil samples taken from the moon during Apollo 17, almost two decades before he was born. As he became more familiar with looking at the fine grains under the microscope, he also began to use his tweezers to sift out something else that caught his attention -- a handful of tiny crystals flecked with black spots.
Today, the end result of Weinreich's painstaking summer task is being announced -- a paper in Science Express, a top journal, that shows that parts of the moon's interior are as wet as the upper mantle of the Earth.
It's the latest finding in what Benjamin Weiss, an associate professor of planetary sciences at MIT, calls "the new era of lunar water" -- in which people are beginning to rethink the dogma about how wet the moon is, and even how our closest neighbor came about in the first place.
"I think this is extremely important -- and I think the most important issue is what does it mean for the origins of the moon," said Weiss, who was not involved in the research. "It makes you wonder how many other bodies weíve inferred to be dry in the solar system are, in fact, dry. Thereís small bodies, there's Mercury, all these other rocky bodies in the solar system which appear to be dry on their surfaces -- it makes you wonder whether deep in their interiors, they are hiding substantial reservoirs of water."
The idea that the moon was dry -- and had been for billions of years -- has been a key part of the theory of how it formed in the first place. The thinking goes that about 4.5 billion years ago, a massive collision occurred between a miniature, nascent Earth and an object about the size of Mars. That violent jolt ejected a disc of molten debris that would become the moon, and because of the heat generated in the collision, any water would have evaporated and escaped into space.
But about five years ago, Alberto Saal, an associate professor of geological sciences at Brown, decided with collaborators to try out a technique he had been using to understand the composition of the Earth's interior -- examining glass beads formed during volcanic eruptions -- on lunar soil. He thought it would be possible to find traces of water or other volatile chemicals, so he wrote an application to NASA requesting approval to study lunar samples.
Saal recalls that his colleagues laughed at his naivete -- everyone who studied the moon thought they already knew the answer: he would find nothing. NASA rejected his request twice.
"They said, 'We know there is no need,' -- and that [made] me a little bit upset," Saal said. So he persisted and finally got NASA to change its mind.
From those samples, Saal and colleagues published a provocative paper in Nature that found traces of water present in beads. Based on a model, they predicted there was much more water than that in the moon's interior. The claim set off debate in the scientific community, and Saal said, "We got hammered" with criticism.
So when he met a particularly bright student in his freshman seminar on volcanoes, he asked him if he'd like a research job that summer. That student -- Weinreich -- agreed, and Saal started him off sorting samples taken on Earth and preparing them for analysis.
"I thought that would take the whole summer -- one month later, he comes and itís done," Saal said. "I said, 'No, itís not possible.' ... He is working at a level I have not seen."
So Saal gave Weinreich a precious vial of lunar soil and asked him to pick out the orange volcanic glasses.
"It was definitely a little bit nerve-racking knowing that if I made a mistake there wasnít really any way to get those things back," Weinreich said. But he began the task -- and also used his growing expertise to set aside interesting anomalies, like a handful of crystals with black specks, to show his advisor.
Saal was instantly excited. The crystals Weinreich found, called olivine, had essentially formed a kind of armor around a drop of molten rock from the early life of the moon. That meant that if there was water or other volatile material that had come from the moon's interior, it could be found by analyzing the speck.
Weinreich painstakingly polished the samples and they were sent to Erik Hauri, a staff scientist at the Carnegie Institution of Washington, an expert with a very precise instrument that could aim a narrow beam of charged atoms at a sample, and then analyze the composition of what was removed.
Together with a collaborator at Case Western Reserve University, they found amounts of water equivalent to that found in parts of the Earth's mantle -- just as they had predicted years earlier. Now, the team plans to analyze more samples from more spots on the moon. In recent years, satellites have found evidence of water on the surface of the moon, and the scientists hope that it will be possible in the future to determine whether that ice was deposited there by comets as has been thought -- or whether it came from the moon itself.
"Itís really exciting," said Weinreich, now a junior who is majoring in chemical physics. "Itís interesting to be doing something that has this air of excitement."
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