Researchers Take Peek Inside a Comet Early results from NASA's mission to crash a probe into a comet have some surprises for comet specialists.
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Researchers Take Peek Inside a Comet

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Researchers Take Peek Inside a Comet

Researchers Take Peek Inside a Comet

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You're listening to TALK OF THE NATION/SCIENCE FRIDAY. I'm Ira Flatow.

A bit later in the hour, happiness.

But first, something that--well, maybe you could describe this as happy. A lot of scientists are happy about it. Last July, scientists deliberately smashed a space probe into the side of a passing comet, Tempel 1, to see what it was made of. This week, scientists published the first results from the Deep Impact Mission and what they found was a big--was sort of a bit surprising. For one thing, this comet at least is a pretty fluffy, dirty snowball.

Joining me now to talk about the finding is Lucy McFadden. She is a co-investigator on the Deep Impact Mission and an associate research scientist in the department of astronomy at the University of Maryland in College Park.

Welcome to SCIENCE FRIDAY, Dr. McFadden.

Dr. LUCY McFADDEN (Deep Impact Mission; University of Maryland): Thank you, Ira.

FLATOW: So what...

Dr. McFADDEN: Great to be here.

FLATOW: Thank you. This was kind of surprising what you found, was it not?

Dr. McFADDEN: Well, we've always expected that comets are very, very light and not very dense, very porous. So we were expecting it but maybe not to the same magnitude that we actually were able to measure.

FLATOW: Describe the comet for us, what it looked like and how fine were these particles you found?

Dr. McFADDEN: OK. Well, as we approached the comet, as the spacecraft was traveling closer and closer to the comet, we saw this irregular-shaped object sort of pop out of the gas and dust that's released in the coma of the comet and we saw the--well, we didn't have much time to look at the comet before we hit it, so we were looking afterwards and saw this surface that has features on it--circular features which we believe are craters. There's this rough terrain that looks very old and like it hasn't changed since the beginning of the solar system. And then there's material there that's very smooth and looks very new and has no craters on top of it. And then when we hit it, we saw this huge brightening--immediate brightening which was scattered light off of all these microscopic dust particles. And we knew we'd release dust, but we just never anticipated we'd release so much dust. And it just stayed around. It took a long time for the dust to clear. And by the time it cleared, the spacecraft had flown by.

FLATOW: So instead of being like a compact, hard snowball--a dirty snowball, it was sort of like a snowdrift.

Dr. McFADDEN: Yeah. Yeah. Good way of expressing it.

FLATOW: And what about these smooth areas on the comet? Was that surprising, too?

Dr. McFADDEN: Well, it was surprising because they're not--the whole comet isn't totally covered over with this smooth stuff. We can envision that this smooth stuff might be fallback from normal comet outgassing, but yet it doesn't cover the whole surface of the comet. It's just in two localized regions. And so that's sort of--you know, we're just trying to explain that.


Dr. McFADDEN: So we're sort of scratching our heads over that.

FLATOW: Yeah. A lot to scratch your heads on...

Dr. McFADDEN: Yeah. Yeah.

FLATOW: ...on this one. That's always the exciting part, isn't it?

Dr. McFADDEN: Oh, absolutely. It's--we're really in this phase where people who like chaos are really having a good time. Those of us who like to work in an orderly and logical environment are really struggling. We think we learn something one day and find out, `Oh, it's an artifact on a camera,' and then--you know, but we've got to be careful, maybe we're making some new discovery and we don't want to dismiss it as an artifact on a camera or something.

FLATOW: Does that happen, really? `This can't be true?' I mean, `It's so unexpected, it must be dust on the lens or something'?

Dr. McFADDEN: Well, you know, sometimes in some cases, though...


Dr. McFADDEN: ...but not with the images that we've released.

FLATOW: Right.

Dr. McFADDEN: That's why it takes a while to--you know, to prepare the material and release it. We have to, you know, sort of vet it among each other and then make...

FLATOW: Right.

Dr. McFADDEN: ...sure we can persuade each other that what we think is true is actually true. So we...

FLATOW: We're talking with Lucy McFadden, who's co-investigator of the Deep Impact Mission.

Now tell us about the actual composition. There was another surprise of what material it was made out of.

Dr. McFADDEN: Yeah. Well, we see--we determine the composition from spectroscopy. We have an infrared spectrometer onboard and we were able to observe the comet before impact and then again during and after the impact. And so our first spectra that we look at show emission bands due to hot water. So hot water vapor as well as hot carbon dioxide vapor. So this is a short-term phenomenon that shows us that we're seeing the initial heated material that came off in the first second after the impact. We also see heated grains of carbon-bearing minerals which we call hydrocarbons. Mainly we call them that 'cause we don't know the details of what's in those spectra.

FLATOW: I'd heard also that you might have found minerals that could only be made in a crucible of heat, which how do you find that out from deep space?

Dr. McFADDEN: Yeah, I know. Well, that's--we were lucky; at the time of our impact we had not only data from our spacecraft, but we had data from the Hubble Space Telescope and the Spitzer Infrared Observatory.

FLATOW: You had something like 80 telescopes looking at this.

Dr. McFADDEN: Oh, and all the ground-based telescopes around the world.

FLATOW: Right.

Dr. McFADDEN: So it was quite striking. So the Spitzer observations gave us some signatures of a lot of other materials that were sort of surprising to us. And so that was sort of exciting, evidence of material, oh, silicates and some...


Dr. McFADDEN: ...hydrocarbons and things. So...

FLATOW: But they would require heat to be formed, silicates, would they not?

Dr. McFADDEN: Well, that's correct.

FLATOW: So where are you going to get heat from out in the frigid outers of--where comets come from?

Dr. McFADDEN: Well, the--well, that's a very good question, and it had to have come from the exploding star from which the solar nebula formed. So it comes from the beginning of the solar system when there is this--when this gas and dust collected. So it did come from the very beginning, from the early stages of solar system formation.


Dr. McFADDEN: And that's what's so dramatic about it.

FLATOW: Wow. That's a--we're talking billions of years old, the stuff.

Dr. McFADDEN: We are. Back four and a half billion years ago and, you know, we don't have any way of telling exactly when this happened, but it had to have been very early in the solar system's formation.

FLATOW: Let's go to the phones. Hi, Ron, in Madison. Hi, Ron.

RON (Caller): Were comets and other larger planetesimals the origin of the water in the Earth's ocean, also that ice belt around the equator of Mars that was there about five million years ago--was it from comets? And what perc--do you have any idea on the percentages how much of your comet was water, how much hydrocarbons, how much silicate, you know, etc.?

Dr. McFADDEN: Yeah. OK. Well, it is a viable theory that the water here on Earth and elsewhere in the solar system was brought by the icy planetesimals, the comets, as the debris was being swept up and as the planets were forming. We cannot prove that from these observations. We didn't have the right kind of--the precise spectrometers that we need to determine that, but it's still a viable hypothesis that the water on Earth came from the comets.

FLATOW: There'd have to be a lot of comets for all that water, wouldn't there?

Dr. McFADDEN: Yeah. But it's...

FLATOW: What about the outgassing, the big burp theory that it was coming from deep below the Earth?

Dr. McFADDEN: Well, right. That's--OK, that's--again, there is more than one hypothesis, and we need to make the right measurements to distinguish between those.

FLATOW: Right.

Dr. McFADDEN: And that's another measurement for another project...

FLATOW: Right.

Dr. McFADDEN: another time.

FLATOW: Right. Let's move on, 'cause I have so many questions and so little time.

Dr. McFADDEN: Great.

FLATOW: But the fact of the hydrocarbons, we've always talked about that as being the primordial building blocks of life that might have come to Earth from comets. Does this really lend evidence to that idea?

Dr. McFADDEN: Well, again, it lends evidence to it, but, you know, there's a long way between these carbon-bearing compounds that have carbon-hydrogen bonds in them and the complex biochemistry that produces proteins and RNA and DNA. So, again, we're making progress, but again, there's still many steps to--or many pieces of the puzzle to put together.

FLATOW: Right. Right. You know, you were also author of--one of the authors of a report this week published about the asteroid Ceres.

Dr. McFADDEN: Yes.

FLATOW: The largest asteroid we know about in the asteroid belt. Tell us about that.

Dr. McFADDEN: OK. Well, Ceres was discovered in 1801 and it's been in orbit--it was forming back at the beginning of the solar system, too, and it failed to grow into a larger planet mainly because of the gravitational forces of Jupiter that knocked it--kept it from accreting and acquiring more material. And this week we published results from the Hubble Space Telescope that allowed us to measure the exact--the precise shape of Ceres. And what we found is that it's almost spherical but it's not quite. It's oblate. It's sort of like--somewhat like a hamburger shape. And the difference between its equatorial axis and its polar axis indicates that the inside of Ceres is differentiated so that something--there's been some heat mechanism or some mechanism that has brought heavier material to the center of Ceres, and then there's some material holding it up, sort of distorting its shape as well.

FLATOW: How far away out of our solar system, let's say from Pluto, would this be?

Dr. McFADDEN: Oh, no. Ceres is just past Mars--between Mars and Jupiter.

FLATOW: Could we call it another little planet?

Dr. McFADDEN: Well, we could call it another little planet, but we have to give it a perspective of scale, because it's about--let's see, it's about one-third the size of the moon--of the Earth's moon.

FLATOW: That's pretty small.

Dr. McFADDEN: So it's pretty small. But yet it is the first object in the asteroid belt that is--well, that we found that--where its shape has deformed it in the combination of its rotation rate, one day on Ceres is nine hours and...

FLATOW: Right.

Dr. McFADDEN: So its shape has deformed. And it has the charac--some characteristics of a planet because it's differentiated.


Dr. McFADDEN: But it's really not big enough to be one.

FLATOW: One quick question and then we have to go: Where do you--do you weigh in on Pluto as a planet?

Dr. McFADDEN: Oh, well, that's just semantics, so I'll discuss that in an English class with you.

FLATOW: All right. You're a diplomat also.

Dr. McFADDEN: I try.

FLATOW: All right. Thank you very much for taking time to talk with us.

Dr. McFADDEN: OK. My pleasure. OK.

FLATOW: Dr. Lucy McFadden is co-investigator on the Deep Impact space mission and an associate research scientist in the department of astronomy, University of Maryland in College Park, talking about comets and who knows, you know, there's a mission that's going to be going out to another comet, a European Space Association mission, it's going to land on a comet. Maybe this will be fluffy. And if it's this fully, maybe it'll sink into that comet as the same as Tempel 1--we'll find out when it gets there.

We're going to take a short break. When we come back, we're going to talk about happiness. What is happiness? What makes you happy? Can pain make you happy? Maybe some people find that to be happy--make them happy. A couple of authors are with us. We'll take your questions and your opinions on happiness. Don't go away. We'll be right back.

I'm Ira Flatow. This is TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

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