Comet's Dust Holds Basic Ingredients Of Life

NASA's Stardust spacecraft flew billions of miles to snatch dust from the comet "Wild 2," returning samples to Earth in 2006. Now researchers have found amino acids, the building blocks of life, in the dust. Stardust principal investigator Don Brownlee discusses the discovery.

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IRA FLATOW, host:

Up next, a listener. A listener called us a few weeks ago.

(Soundbite of telephone ringing)

CAROL(ph): Hi Ira. It's Friday, August 28, Carol in Bartlesville, Oklahoma. I heard that the Stardust probe has detected glycine in that cometary tail. I don't have a computer - can you believe it? - or any science training, really, but I'm really interested in that, and I haven't seen anything in the popular press. Could you sometime in the next few years give us an update on what actually is happening with the Stardust thing, that probe thing? Thank you, Ira. Help me.

FLATOW: And we're going to help Carol because, as they used to say on television, you asked for it. We're going to go straight to source to answer this question. The principal investigator for the Stardust mission joins us.

Don Brownlee is professor in the department of astronomy at the University of Washington in Seattle. He joins us from KUOW. Welcome back to SCIENCE FRIDAY.

Dr. DON BROWNLEE (Professor, Department of Astronomy, University of Washington Seattle): Thank you very much.

FLATOW: Can you help Carol? Whatever happened to Stardust?

Dr. BROWNLEE: Well, you know, we brought back samples a little over three years ago, and we've had a fabulous scientific result from many studies. There have been over 200 scientists around the world that worked on these. And we found some incredible things, including the smell of life, since you've been talking about the smell of death.

FLATOW: And that was glycine. This is an amino acid.

Dr. BROWNLEE: Glycine, yeah. One of the most recent things was in the news just a week or so ago, was that a group of three scientists at the Goddard Space Flight Center in Maryland discovered glycine, an amino acid, in this comet sample, a sample of a comet that formed at the edge of the solar system, out past Neptune and Pluto.

FLATOW: Wow, and do we know where it came from? I mean, was it made on the comet? You know, was it picked up from some other place?

Dr. BROWNLEE: It probably was made somewhere out there and then went in to form the comet along with rocks and ices and other organic materials 4.5 billion years ago, when the comet formed, and it's very exciting.

You know, amino acids are a fundamental building block of life. It doesn't require life to make amino acids. Amino acids were found in primitive meteorites actually in 1969, with a meteorite that fell in Australia called Murchison. But there was a big wonder whether amino acids would have formed at the edge of the solar system, out where the comets formed, past the orbit of Neptune.

FLATOW: How do we know that it didn't start out on the spacecraft to come back on…?

Dr. BROWNLEE: On this, the glycine - it's actually a miracle to be able to do this. When the sample - when the spacecraft was launched, we had no expectation that anyone could ever actually measure something like amino acids in this pinch of comet dust that we were bringing back. But over the last three years since the samples came back, they developed these fabulous techniques. And they…

FLATOW: All right, Dr. Brownlee, I'm going to stop you there because we have to take a break, but you'll come back right after the break.

Dr. BROWNLEE: Right, okay. I'll tell you the secret then.

FLATOW: Yeah, tell us the secret, what happened over those years to allow them to find this glycine on there? Interesting story. Stay with us. We'll be right back with Don Brownlee at the department of astronomy, University of Washington in Seattle.

1-800-989-8255 is our number. Also, you can Tweet us @scifri, @-S-C-I-F-R-I. Stay with us. We'll be right back.

(Soundbite of music)

FLATOW: You're listening to SCIENCE FRIDAY from NPR News. We're talking this hour about NASA's Stardust mission, what we've learned from studying those tiny grains of comet dust.

Here to talk with us - we've been talking with Don Brownlee. He was principal investigator for that mission, and he's professor in the department of astronomy at the University of Washington in Seattle. And before I rudely interrupted, he was talking about the discovery of glycine and how you say you never expected to find something like that.

Dr. BROWNLEE: No, we didn't expect that the sample would be big enough to match the techniques that were available, but the scientists at Goddard Space Flight Center refined techniques and remarkably were able to prove that there are extraterrestrial amino acids in the comet. And they did this on the basis of the isotopic composition of carbon that was different than for terrestrial materials.

FLATOW: So this means that this must be - if it's out on this comet that's way out there, way in outer space, it might be as old as the Earth itself, floating around…

Dr. BROWNLEE: Absolutely. The comet - the reason we went to the comet is because it is believed to be the best-preserved building blocks of the solar system, and it's 4.567 billion years. So it's actually older than anything on Earth.

FLATOW: So, and the theory is that it's possible that the countless number of these comets not only brought water to Earth but now may have brought these amino acids, the building blocks of life.

Dr. BROWNLEE: Yeah, comets definitely delivered water to Earth. They may not have delivered most of the oceans, but they delivered some of the oceans. And amazingly enough, even today we have 30,000 tons of comet and asteroid debris that lands on the Earth every year.

So throughout the entire history of Earth, we've had this sort of (unintelligible) of stuff coming in from space, which includes amino acids, both from asteroids that form closer to the sun, as well as comets that formed out near Pluto.

FLATOW: And how do you get an amino acid to form on a comet?

(Soundbite of laughter)

Dr. BROWNLEE: That's a good…

FLATOW: Very slowly, as they say…

Dr. BROWNLEE: That's the big question. But one of the real issues, even though amino acids were found in meteorites, there are some meteorites that are very carbon an organic rich that do not contain amino acids. There's a meteorite called Tagish Lake, weighed 100 tons before it broke up over the Yukon. And six percent of that meteorite is carbon, but the amino-acid content is basically zero.

And so why did some bodies have it, and some of them didn't? So there was some thought that maybe comets would not contain amino acids, but that's clearly not the case. It was proven that it existed in our comet.

FLATOW: Do we have any theories about how they formed on the comets?

Dr. BROWNLEE: Well, one idea is that they, you know, formed in the inner-solar space, in the materials actually older than the solar system. But one of the astounding things that we found on this Stardust mission was that most of the material, most of the mass of the comet we went to, actually formed within our solar system.

The expectation, and the reason we called the mission Stardust, the dominate material would have been formed right on other stars. You know, comets form way out beyond the most distant planets, always cold, always small, super pristine. But we found that most of the material in the comet, at least of the rocky materials, were made in the inner solar system, probably interior to Earth's orbit, and were carried all the way out there past Pluto.

FLATOW: So you had this rocky core that goes out and then gets a crust of ice around it outside there and brings it back?

Dr. BROWNLEE: No, no, it's not a rocky - its rocky core, it's little, tiny rocks and dust particles that - when the solar system was forming, it was a disk called the solar nebulous, some forms of metal, and there was a circulation pattern where stuff flew outwards. Even though some stuff's going inwards, other stuff flew outwards. So the comets are this fantastic mix of things actually that formed across the entire early solar system, and then they were packed in ice, including those amino acids, and frozen for the entire age of the solar system for us to find an analyze.

FLATOW: 1-800-989-8255 is our number, if you'd like to talk about the comets, and also you can Tweet us, @scifri. That's @-S-C-I-F-R-I. Do we know what the rocky materials in the comet are made of? Are they crystals? Are they minerals? Or what's in them?

Dr. BROWNLEE: Most of the particles that we collected were actually rocks. Rocks are things made out of multiple minerals. Even though the particles, you would think, were fairly small, they contained very small mineral grains, and they tell an incredible story. Many of the particles found were actually igneous. They were molten rocks at the time they formed, which means they formed at extremely high temperatures. And we also found examples of the highest temperature, most refracted materials that were ever in the young solar system, and we found this in a comet.

Comets were, you know, formerly most famous because they contain ices that formed only tens of degrees about absolute zero, but they also - now we know they contain rocks that were actually white-hot and some of them actually molten at the time that the formed, very violent - so the comet's this incredible mixture of rocks formed at a high temperature of violent conditions, ices that formed at really low temperatures and organic materials like amino acids like glycine that formed by an unknown process.

FLATOW: And they said the only way you would know that is this mission. Where did they go, to Wild 2 comet?

Dr. BROWNLEE: Wild 2, yeah. It's spelled wild, but it's pronounced vilt(ph).

FLATOW: And you had to go out and bring it back, right? You just couldn't wait for it to get here. It shows that you need to have a return sample mission for these things.

Dr. BROWNLEE: To do this kind of work - I mean, comets, you know, if you look at them from a distance of even feet away, they're just black rocks. They look like a pile of charcoal. In order to get at this stuff, you have to get it in the lab where you can study it basically at atomic and molecular resolution. Almost everything we know about ancient Earth history was obtained by studying rocks at very, very fine, fine, special scale. And that's what we can do on extraterrestrial bodies that we actually return to Earth.

FLATOW: And you are the only people, besides the folks who went to the moon and brought stuff back, who've ever brought anything back from space, right?

Dr. BROWNLEE: Yeah, yeah.

FLATOW: Isn't that amazing?

Dr. BROWNLEE: Yeah, it is. You know, it's kind of fun. I was at the Air and Space Museum on Friday actually looking at our little spacecraft. And if people are interested, they can actually see the sample return capsule. It's right there under the wing of the Spirit of St. Louis.

(Soundbite of laughter)

FLATOW: What a contrast.

Dr. BROWNLEE: The museum was quite intrigued by it because they deal in artifacts, and for planetary missions, we are the only planetary mission that actually came back. The Apollo missions came back from the moon, but all the other probes, you know, the Jupiter and Mars and Venus, they're one-way shots. You know, no astronaut's on board. So they didn't come back. We're the only thing that came back.

FLATOW: Yeah, and you parachuted down, but the mother ship is still out there.

Dr. BROWNLEE: The mother ship is still out there, and it's flying past a comet in about a year.

FLATOW: Nothing you can learn from it anymore now that it's done its mission, if it goes by another…?

Dr. BROWNLEE: Well, we can't collect any samples because we only had one collector and one sample return capsule. But the spacecraft is actually flying past the comet that another NASA mission called Deep Impact cratered, and so we're using the spacecraft, which is still in space, still operating, to fly past that comet and image the crater.

FLATOW: Let me see if I can get a call on here from Steve(ph) in Syracuse. Hi, Steve.

STEVE (Caller): How are you all doing?

FLATOW: Hi there, go ahead.

STEVE: I had an observation more, and I think you were just about hitting on it, and just a quick setup is one of my sons is an Air Force pilot and sort of aspires to astronaut, and I'm not, therefore, anti-astronaut, but I think if this discussion doesn't really validate non-human space exploration, I don't know what can because this, the value of this return is just remarkable.

I think it's - correct me if I'm wrong, if anybody knows - like 100 to one just in terms of non-human space exploration, the value you get back from that than, you know, human.

FLATOW: Yeah, thanks, Steve. Do you agree?

Dr. BROWNLEE: Well, this is a complicated issue. I feel both ways.

FLATOW: You don't want to get into hot water on this one.

Dr. BROWNLEE: Well, no, I think people can do amazing things in space, but there are a lot of things in space that people cannot do. No one's ever going to walk on the surface of Venus, and probably no one's going to walk on the surface of a comet, not for a long time, because you can do it actually better robotically. But you know, if you're going to the moon or Mars, it's more of an open question. It's a big question that some of these countries are struggling with right now.

FLATOW: Well, we might have to push one out of the way, though, a comet or an asteroid that might be headed…

Dr. BROWNLEE: Yeah, that's the really interesting thing is that the comets and asteroids do hit the Earth all the time as little particles - I said 30,000 tons per year. But the big ones come in every once in a while, and you can ask the dinosaurs what they thought about the last big one that hit 65 million years ago that caused their extinction.

Comet and asteroid impacts are the one certain thing that can kill us all, I mean all animals on the planet, unless we humans come up with a little scheme for pushing these things out of the way so it'll miss us.

FLATOW: At least we know how to get there now. Thank you, Don…

Dr. BROWNLEE: Yeah.

FLATOW: …for taking time to be with us. Don Brownlee is the principal investigator for NASA's Stardust mission. He's also a professor in the department of astronomy at the University of Washington in Seattle.

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