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Fifty years ago this month, astronauts left their footprints on the moon. What they brought home was rocks. Nearly half a ton of moon rock was collected by the six Apollo missions to the lunar surface. NPR's Nell Greenfieldboyce looks at what happened to those rocks and why scientists still want to go back and get more.
NELL GREENFIELDBOYCE, BYLINE: When Darby Dyar was a kid, she remembers watching the Apollo astronauts return. She'd see their capsule bobbing in the ocean as the astronauts emerged with some precious cargo.
DARBY DYAR: They climbed out, and then they very carefully took the lunar samples and put them in the little rubber boat.
GREENFIELDBOYCE: You remember watching that on TV?
DYAR: Oh, absolutely.
GREENFIELDBOYCE: The box holding the rocks looked like an Igloo cooler. She never thought that someday she would study those rocks.
DYAR: I was growing up in Indiana in the 1960s. Girls didn't do science. I never saw a woman scientist.
GREENFIELDBOYCE: She set out to be a journalist but ended up majoring in geology. As a college student, she started working for a researcher who'd gotten some of the newly arrived moon rocks. She remembers how he kept them under lock and key.
DYAR: We all knew that the filing cabinet in his office was the safe. You know, I remember my hands shaking the first time he said, well, you know, grind this up and put it in the sample holder. And I was like, are you sure?
GREENFIELDBOYCE: Dyar is still studying moon rocks. She's a researcher with the Planetary Science Institute who's also a professor at Mount Holyoke College. At her lab there, she shows me a bunch of lunar samples. Some are thin, translucent slices of rock on microscope slides. Others look like gray pebbles in tiny glass vials. A few vials look empty.
DYAR: If you had the microscope, you could look at these vials that seem to be empty, and in them, you would find tiny, single crystals of lunar samples, which we carefully save because we have to return every speck of this to Johnson Space Center when we're done.
GREENFIELDBOYCE: Johnson Space Center in Houston, Texas, is the chief repository for Apollo samples. The rocks and dirt are stored in special cases in vaults. Ryan Zeigler is the curator. He says the Apollo astronauts collected 842 pounds of lunar material.
RYAN ZEIGLER: Eight hundred and forty-two pounds is a couple of refrigerators' worth of samples in terms of sheer volume and weight.
GREENFIELDBOYCE: He says a tiny fraction of all this was destroyed in analytical experiments. Some of it is on display, like in museums. But the vast majority is available for study.
ZEIGLER: There were 2,200 individually numbered samples that came back, and we've looked at 2,194 of them. So we only have six unstudied samples from the moon.
GREENFIELDBOYCE: Of the unstudied ones, a few are pristine. They were vacuum sealed on the moon and have never been opened. NASA was waiting for technology to advance. And now the agency says it's time to open one.
ZEIGLER: It's not exactly because it's the 50th anniversary, but it sort of is.
GREENFIELDBOYCE: NASA recently picked six science teams to study these precious rocks. One of the lucky scientists is Dyar.
DYAR: I think we knew that there had been some samples put away for future uses. And, boy, I remember as a graduate student thinking, man, I wonder what that could be. What will we be doing in 40 years?
GREENFIELDBOYCE: What she'll be doing is studying tiny glass beads that formed during ancient eruptions to learn about volcanic activity.
Already, lunar samples have told scientists a lot about how the moon formed when a giant body hit the early Earth. But they've also learned about the rest of the solar system by dating rocks from lunar craters. They could tell when different-sized meteorites hit the moon, which helped them understand the history of other planets that were being similarly bombarded.
DYAR: So it's really the underpinning of a huge amount of planetary science, just being able to relate the size of the crater to how old it was.
GREENFIELDBOYCE: NASA is aiming to go back to the moon, maybe as soon as 2024. I asked Dyar if she could go to the moon and get any rock, what would she want? She says in the South Pole, there's a giant crater where some massive impact seems to have punctured through the moon's crust.
DYAR: And it exposed rocks that we don't see anywhere else on the surface of the moon. I would love to go there. And it would be really, really important to understand, is the interior of the moon really what we think it is?
GREENFIELDBOYCE: She sometimes marvels at how far the study of lunar materials has come over her lifetime.
DYAR: I've also been known to get the samples out on the night of a full moon and stand there in my office when I can see the moon out my window and think, look; you know, I got part of you here. You know, we're onto you.
GREENFIELDBOYCE: NASA will probably be ready to open the pristine, sealed lunar sample sometime next year.
Nell Greenfieldboyce, NPR News.
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