LAUREN FRAYER, HOST:
This is Lauren's log, stardate December 31, 2017. Captain Lulu Garcia-Navarro is away, but we continue the mission to explore matters of space, the stars and the universe.
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FRAYER: As we near the end of 2017, let's take stock of the most momentous space stories of the year. There were some big ones. NPR science correspondent Nell Greenfieldboyce joins me now to help us look back. Hi there, Nell.
NELL GREENFIELDBOYCE, BYLINE: Hey.
FRAYER: So probably the science story that grabbed the most attention, at least here in the U.S. this year, was the Great American Eclipse. Now, I'm assuming you didn't miss this.
GREENFIELDBOYCE: Oh, absolutely. There's no way I was going to miss this. And the thing is, I had talked to a lot of eclipse chasers before, so I thought I knew what I was getting into. But when the moon went in front of the sun and the whole sky went dark and there was this other worldly sort of circle of white light in the sky and there was sunset in the middle of the day - I mean it was crazy. People were screaming.
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UNIDENTIFIED WOMAN: (Screaming) Oh, my God.
FRAYER: And you were not the only one.
GREENFIELDBOYCE: No. There was something, like, 200 million adults who went and saw this thing. And I mean, so for me, not only was it a science story that gripped the nation, it was a moment where we all really got to share something.
FRAYER: So OK, let's head a little bit farther away from the Earth to Saturn, where we saw the fiery end of NASA's Cassini spacecraft. Remind us what that was and why it's such a big deal.
GREENFIELDBOYCE: So Cassini had been in space for, like, 20 years, OK? It took, like, seven years just to get to Saturn because Saturn is so far away. And then this spacecraft spent 13 years going around Saturn and learning a lot, not just about Saturn but mainly about its moons, OK? Saturn has got a bunch of moons.
FRAYER: I've heard about the rings, but I didn't know about the moons.
GREENFIELDBOYCE: It's got big moons, and Titan is bigger than Mercury. And from this mission, we learned that it's got this weird cycle on it that's sort of like Earth's water cycle. But Titan is so cold that instead of water, what it is is liquid methane. So there's, like, lakes of liquid methane and liquid methane rain and liquid methane clouds. And then there's this other moon called Enceladus, and Cassini learned that it's got, like, geysers of water just, like, shooting off the surface, which means there's some sort of subsurface warm ocean, which is now seen as, like, one of the best places in the solar system to look for life. So Cassini gave us all of this great information, and then whammo, it was just over.
FRAYER: It gave us all that information, and now it's gone.
GREENFIELDBOYCE: It was running out of fuel. And they weren't going to be able to control it. And they worried that it actually might get out of control and smash into one of those moons and contaminate it with Earth microbes. So they're, like, better just to kill it off.
FRAYER: So we euthanized Cassini.
GREENFIELDBOYCE: That's right. Yeah.
FRAYER: And now let's go even farther out into space - 130 million light years away, to be precise. What happened out there?
GREENFIELDBOYCE: So that's these two colliding neutron stars. And neutron stars are these crazy stars. They're only the size of a city, like New York, but they've got more mass packed in there than our sun. So these two incredibly dense things slammed together, and they generate ripples in space time. And so this was the first time this type of event had ever been detected by our gravitational wave detectors. And because of this, astronomers all around the world, thousands of people, were able to point their telescopes and actually see this event as it happened. It was, like, spewing out heavy elements, like gold and platinum, in this vast solar system-sized cloud of radioactive waste. It was one of the biggest events in astrophysics in years and years and years, maybe ever. And that's the kind of thing that scientists are hoping to see more of in the year ahead and in the years ahead.
FRAYER: Wow. So 2017 - eclipses, spacecraft and Saturn, colliding neutron stars. I look forward to seeing what happens in 2018.
GREENFIELDBOYCE: Nobody knows what it'll be.
FRAYER: NPR's science correspondent Nell Greenfieldboyce, thank you very much.
GREENFIELDBOYCE: Thank you. Transcript provided by NPR, Copyright NPR.