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Stardust: Heading Home

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The treasures of Stardust are heading home.

I'm Jane Platt and this is a podcast from JPL -- NASA's Jet Propulsion Laboratory in Pasadena, California.

Nearly seven years ago, the Stardust spacecraft launched on its mission to collect comet dust and dust from between the stars. With its precious cargo captured and carefully stowed away, Stardust is now heading home. Engineers are preparing for the spacecraft sample return capsule to land in the Utah desert on January 15, 2006. Somebody who's very anxiously awaiting a peek at the treasures inside is Dr. Don Brownlee. He's the Stardust principal investigator, and he joins us today from the University of Washington in Seattle.

Don, some of our listeners have been following Stardust through the years, but others are just learning about it right now. Just so we can get everybody up to speed, can you give us a quick recap of what Stardust has been doing since its launch in February 1999?

BROWNLEE: OK, we are a sample return mission, so our primary goal is to collect samples and bring them back. But in the intervening seven years, we've had quite a trip. We've gone three loops around the sun, we did an Earth flyby, we flew past a famous asteroid named Anne Frank, and of course we also took fabulous pictures of the comet during the time that we were collecting our hundreds of thousands of particles. Stardust is now streaming back to Earth and will be here on January 15.

Q: Okay, and that comet flyby was two years ago. You gathered a lot of dust, as you mentioned. In the wee hours of January 15, those samples of comet dust and also some interstellar dust are coming back to Earth. Briefly tell us what will happen in the wee hours of that morning.

BROWNLEE: Well, the capsule will enter the atmosphere at a high altitude and at about 100,000 feet, a small parachute comes out at over, at supersonic speed of about Mach 1.4. It's called a drogue chute. And then later at about 10,000 foot altitude, the main chute comes out and it gently hits the ground at about 15 feet per second. And it's picked up by a helicopter crew, taken back to a cleanroom, where part of this capsule is de-integrated, and then the samples then fly on an airplane to Johnson Space Center in Houston, Texas.

Q: As you await the big day, you've put a lot of time and energy into this mission. What's running through your head?

BROWNLEE: Well, we are very excited, and we're actually thrilled because you know, you start a mission like this, everything is unknown and there are many, many difficult things ahead of you. We are in a position now that is very envious, because we have done almost everything there is to do on this mission, and almost everything has worked extremely well. It's sort of a charmed mission, and so we're really looking forward to the samples. The samples are a new page in science. This is a sample return mission of solid materials from space, and it's a rather historical event, and I'm very excited about it.

Q: Why are comets so intriguing to you and to many other scientists?

BROWNLEE: Well, comets are intriguing for a variety of reasons, but my personal strong interest in them is that comets are bodies that formed at the very edge of the solar system, out beyond the orbit of Neptune, where Pluto is. And they are the best preserved samples of the initial material that actually made the sun and earth and planets and even ourselves. So this is a history project. We are going to the edge of the solar system, collecting the original building blocks of the solar system and bringing them back to our labs. I said we are going to the edge of the solar system, we actually are, even though we only flew halfway to Jupiter. We met halfway, the comet came in from where it was, and we went out to meet it and grab a sample. So even though we only went halfway to Jupiter, we're effectively going to the edge of the solar system as it was four-and-a-half billion years ago.

Q: What is it you hope to learn from these samples that you're bringing back?

BROWNLEE: Well, we believe we will be finding the actual building materials of the solar system. So the number one question is, what are these materials like and how do they compare with extraterrestrial materials we already have in the lab, samples of meteorites and interplanetary dust, most of which come from the inner part of the solar system, where the asteroids are. The mission is called Stardust because it is believed that a significant fraction of material, solid material in comets, are actually stardust, interstellar dust that was formed around other stars, and those particles are actually older than the sun and the planets.

Q: I've heard a percentage relating to humans and stardust, can you rattle that off the top of your head?

BROWNLEE: Well, the relation between humans and stardust, amazingly is that, virtually all the atoms in our bodies were in little grains like the ones we're bringing back from the comet. They were in there before the earth and sun were formed. Stardust, or interstellar grains, form around other stars and they are the vehicle which carry elements like carbon, nitrogen, silicon, and iron and magnesium from place to place within our galaxy. So when stars in new planetary systems form, they form from gas and dust. Virtually all the elements except hydrogen and helium are in the dust, and we have collected some of that stuff and it will be in our lab just after January 15.

Q: Tell me how you're going to study these samples. You've got some very high-tech machinery including one really, really huge apparatus.

BROWNLEE: There's a whole variety of instruments around the world, the samples are distributed to people all over the world to investigate using the very best possible instruments. These instruments include electron microscopes, which weigh tons, and mass spectrometers, which weigh tons, and even nuclear accelerators. The largest instrument that I know that will be used to study this is the Stanford Linear Accelerator, which could produce beams of very finely focused X-rays, and this instrument is two miles long.

Q: About six months ago we had another highly-successful comet mission. Deep Impact collided with a comet so it could study the spray of dust. Explain how Deep Impact and Stardust are basically complementary of each other.

BROWNLEE: Well, they're very complementary. Deep Impact impacted a comet and for a period of about two days there was quite a bit of material ejected into space. The infrared observations, from orbiting telescopes and ground based and infrared measurements on the spacecraft itself, provided a really interesting infrared spectra from the mineral components of the comet. It was a rather spectacular event, releasing all this material. So we will be able to use that data to compare with what we actually see in the lab by studying it directly. And also, we can extrapolate using the astronomical measurements to similar measurements you can make for other comets, and even other clouds of dust around other stars. So what we are doing here, in our solar system, with missions like Stardust and Deep Impact has a terrific application to studying materials that we can view far away with telescopes that we'll never dream of actually visiting with a spacecraft.

Q: There's been a lot of preparation and planning for the sample return capsule descending and landing at the U.S. Air Force Utah Test and Training Range. But despite all the preparation, there's never a guarantee. So assuming everything goes as planned, when will you actually be able to look at the samples?

BROWNLEE: Well, they're landing on the fifteenth, and two days later we plan to open the canister in Houston and the science begins then. The month when we first open that up and peek inside, we will see tracks. The particles are collected in aerogel. It's a very low density, glass-like material, and they produce tracks. Just with your eyeball, looking at those tracks, we'll be able to tell something about the nature and strength of those particles. For instance, hard, strong, mineral particles make very long tracks and the aerogel looks like carrots, carrots and glass. Whereas, fragile particles can break up and make a more chaotic complicated structured track, that don't look like carrots. So almost instantly, just with the eyeball, we will tell something about the comet, just by glancing at the collector in the very first minutes.

Q: I've got a couple of final questions, but it occurred to me that we've really come a long way because comets throughout history have been always fascinating to people, but there was a time when they were very frightening. Tell me a little bit about the history of comets.

BROWNLEE: Comets are fascinating objects in the sky. In the past, people paid a lot more attention to the sky because they didn't have TV and podcasts, and other things to do. And they also lived in a world without electric lights, so the sky was very dark. And people watched the skies all the time, and they were astrology fans, and they were looking for signals in the sky. So imagine you look at the sky, night after night, and you see the stars go back and forth every night, in a regular way. Then those ornery planets that slowly drift from month to month across the sky, passing the stars, and moving in a mysterious way. Then all of a sudden, this strange thing that you've never seen before, maybe once in a lifetime, you'll see a really spectacular comet which will be this great glow in the sky and this ghostly white object that looks like a sword in the sky. And night after night after night, it gets bigger and brighter and brighter and slowly drifts across the sky. And that is an omen, so if you're worried about the death of the king, or invasion of Mongols, or whatever, that's the signal you're looking for. So people were terrified. It depends on how you look at it, I think they're the most beautiful things in the sky, other than maybe sunsets and sunrises.

Q: Anything I haven't asked you that you'd like people to know about Stardust or about this particular comet, which I guess we should mention is called Wild 2. It's spelled like the word "wild," but it's pronounced Vilt 2.

BROWNLEE: It's really exciting to me, that this message, this cosmic library is in a box and it's on the way back to Earth, and we will have it soon and have it in the lab to do whatever we can to try to read those records of our earliest history.

Alright, well, Don, thank you very much for joining us today.

Maybe you can come back after the samples have come back to Earth and you've had a chance to study them and share what you are finding out about them.

More information about the Stardust mission is online at http://www.nasa.gov/stardust . More NASA podcasts are at http://www.nasa.gov . Thank you for joining us today for this podcast from NASA's Jet Propulsion Laboratory.

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