From: Ames Research Center
Posted: Wednesday, April 4, 2007
Astrophysicist Scott Sandford Discusses Stardust Preliminary Findings (Segment 1)
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Jesse Carpenter: NASA study finds new kind of organics in Stardust mission samples. Hi, I'm Jesse Carpenter and you're listening to a podcast presented in three parts from the NASA Ames Research Center. Launched in 1999 the Stardust spacecraft collected dust particles from the tail of the comet Wild 2 in 2004 and returned the samples to Earth in 2006. Today, we have an interview with research astrophysicist Scott Sandford. He's the lead author of the preliminary findings from the Stardust sample return mission. Scott, tell us why would we want to go to a comet to begin with.
Scott Sandford: Well, I think one of the principle reasons why we want to go to a comet is we think that the material that comets are made out of hasn't been processed much since comets formed 4.5 billion years ago, when the solar system formed, and as such, they may be one of the best reservoirs in the solar system of the original, primordial stuff from which everything else in our solar system was made. So a component of this material could be organic compounds, complex organic compounds. And so if material from these comets was rained out on the Earth after its formation, and we think it was, then this material may have played a role in getting life started because these complex organics that are basically falling out of the sky could have participated in all kinds of chemical reactions that could have led on to much more interesting things like us.
Jesse Carpenter: Tell us where the samples came from and how unique that is.
Scott Sandford: Okay, well, the samples came from a comet called Wild 2, which currently is in an orbit where the closest it gets to the sun is not quite the Earth's distance from the sun, and the furthest it gets from the sun is all the way out at Jupiter's orbit. But we collected this material by flying a spacecraft at fairly high velocity through the coma of the comet. And the coma is the cloud of dust participles surrounding a comet. It's the dust particles that ultimately make the tail that most people are familiar with. And so we basically swept up some of this dust as we went piling through this dust cloud.
Jesse Carpenter: Why go to this comet?
Scott Sandford: Okay, well, there are sort of several reasons why we picked Wild 2 as the comet to go to. The more mundane one is it was a comet we could get to. I mean the comet is in an orbit now where the furthest it gets from the sun is Jupiter's orbit. The closest it gets to the sun is getting down near the Earth's orbit. So it doesn't take a gigantic rocket motor to get there. And so one of the reasons we went is because we could get there. However, it turns out that even if it had been harder to get to, this is a comet we would have liked to have gone to because prior to 1974, this comet was in an orbit where the closest it got to the sun was Jupiter's orbit and spent most of its time out by Neptune. But in 1974, it almost slammed into Jupiter, just missed it, and that caused -- Jupiter bent its orbit into the current one, and so this is a comet that has not been near the sun for probably most of its lifetime and has only gotten near the sun a few times.
So it hasn't lost all the volatiles and the ices and the things that come off a comet when it gets near the sun like most other comets. Haley's Comet's been near the sun probably hundreds of times and so when you go to Haley's Comet, the surface you see is not the original surface. It's a surface that's been cooked many, many times. Well, in the case of Wild 2, it's only been cooked a few times since 1974, so this meant that we had a good chance when we got to Wild 2 that we would get a sample of kind of a raw comet, a comet that's not been, you know, slapped around much. And the images we got when we flew by Wild 2 suggests that's the case, that, in fact, we're looking at a very much more pristine surface. And so the hope is that means that the sample we captured is also more representative of the original comet and not of a comet that's been processed over time.
Jesse Carpenter: Are there any preliminary observations you might be able to share with us?
Scott Sandford: We've noticed a number of interesting things. One is that comet dust seems to be a real zoo of things. We see all kinds of particles that clearly formed in different places, possibly at different times, and certainly under different conditions. And so there's a very strong implication that the comet contains components from all over the solar system when it was forming, so when the solar nebula was first making the planets and the sun, there must have been a lot of mixing going on. A solar nebula may have been a big, giant, you know, washing machine at some level.
Jesse Carpenter: So what is significant about this material?
Scott Sandford: Okay, well, it's of great interest to us because we think it is the starting material from which everything was made, and so it tells us something very important about a very important part of the history of our solar system, when it formed. It tells us what it formed from, something about the conditions under which it formed, and so on. And so it really is a kind of Rosetta Stone, in some respects, of extra terrestrial material for us to understand this key component of our history.
Jesse Carpenter: Give us an idea of the size of sample that was typically found in the aerogel.
Scott Sandford: Normally, if you tell somebody you have a mission that's returning a sample to Earth, the first vision everyone has is the Apollo astronauts bringing big boxes of rocks back. But in the case of the Stardust mission, we brought back a modest number, thousands of sub – of micron-sized grains that hit the aerogel, so we're talking about the particles that we collected measuring, being measured in picograms, so a billionth of a gram of material. So if you add our whole sample together, it's much less than a milligram, which doesn't sound like very much material for all that effort, but, in fact, it's plenty of material for what we want to do. The size of a sample you need, to understand it, has more to do with the nature of the sample than the volume of the sample, and the nature of comet dust is to consist of conglomerates of really tiny things. And so if you get a 10-micron grain, that's not much material, but if it contains 10 million sub micron grains that represent the composition of the comet as a whole, then that's enough material. So fortunately for us, since we brought back these modest amounts of material, it's sort of as we expected -- comet dust is very fine-grained, so the material we've got has been very complex, and there's a rich amount of stuff to learn even in a single grain. And the fact we don't have tons of it is not a problem.
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Astrophysicist Scott Sandford Discusses Stardust Preliminary Findings (Segment 2)
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Jesse Carpenter: Welcome to Part 2 of our podcast interview with Scott Sandford from the NASA Ames Research Center.
Tell us a little bit about the team who analyzed the samples.
Scott Sandford: We decided early on that the samples shouldn't be examined just by the members of the Stardust team, but that we should put together a wider team of people from around the world who could bring a whole variety of analytical techniques to bear. And in the end, the preliminary examination team, I believe, had something on the order of 175 scientists on it from around the world. And I'm not sure the total number of institutions involved but it's something like 70 or 80 institutions. I know on the organics paper for the organics team that I led I think the final paper had 55 authors from 31 institutions.
So while NASA certainly deserves huge credit for getting this mission together and paying the bill and getting it there successfully and all of that, the actual analysis of the sample has been opened up to the worldwide community -- I think to NASA's credit -- and it's been a real joint effort on the part of all these folks. And I anticipate in the future, as samples continue to be allocated beyond the Stardust mission, that we'll see this same thing happening -- that we'll see participating by people from all around the world. Scientists from many, many institutions will continue to look at this stuff in much the same way that people from all around the world are free to request lunar samples brought back by the Apollo astronauts, Antarctic meteorites found by ANSMET and so on.
Jesse Carpenter: How rare is it is for us to get something that's this old?
Scott Sandford: Well, certainly there's nothing on that belongs to the Earth that's four and a half billion years old. Every rock on the Earth has been processed since the Earth formed. So there's nothing that old that's the Earth's. Okay, but we do get things that are four and a half billion years old that land on us all the time in the form of meteorites, so in that respect this old material is not super-rare. It's pretty rare -- I mean you don't see that many meteorites lying around. But the fact that this is from a comet and known to be from a specific comet makes it an extremely rare and unique specimen.
And I'd also point out that while most of this material is presumably four and a half billion years old -- so it's as old as the forming solar system -- we have good evidence for a component of meteorites and also in the comet dust that some of the material is older than the solar system. In other words, there are components present in the comet that existed as material before the solar system formed -- so they were in the dense cloud of gas, dust and ice from which our solar system formed before the solar system was a gleam you know, in anybody's eye.
And then as part of that cloud started to collapse into the solar nebula and the planets and the sun started to form, some of that material from that previous phase survived into the comet without any alteration at all. So there are materials in the comet that are not as old as the solar system – they're older than the solar system.
Jesse Carpenter: So does that older material present any unique surprises?
Scott Sandford: Well, I mean, we're always very interested in that because that allows us to see beyond the origin of the solar system. It's like if you watch a movie -- you only know what happens to the beginning of the movie. Well, in this case if you find these materials you can see what happened before the movie, you know? And so in the case of the organics we can see isotopic anomalies in hydrogen and nitrogen so these are ratios of the isotopes of these elements that are different from what we see in the solar system.
They can actually give us clues on what kinds of processes were happening in this original cloud, so they can tell us something about the environment and the chemistry and the physics going on in this cloud before the solar system even started. And in some cases we can find in the minerals isotopic anomalies that go even further back in time than that, and they tell us something about what was going on in a star that's exploding. Okay some, when a supernova blows up and throws stuff out some of that material can form grains and those will have weird isotopic ratios.
And we find grains in meteorites that have these weird isotopic ratios, and so they tell you that this is a grain that's older than the solar system and potentially even older than the cloud from which the solar system came from. And so if that isn't cool, I don't know what is. I don't know how to describe it any more than that! So obviously a lot of us get very excited about that kind of thing. It's a slightly different part of the science -- instead of learning about the formation of the solar system you're learning about processes even beyond that.
But even then, they tell you something about the origin of the solar system because they tell you that when the solar system formed the conditions had to be such that those grains could survive.
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Astrophysicist Scott Sandford Discusses Stardust Preliminary Findings (Segment 3)
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Jesse Carpenter: Welcome to Part 3 of our podcast interview with Scott Sandford from the NASA Ames Research Center.
Tell us why you're so focused on the organics found in the sample return.
Scott Sandford: Well, one of the reasons why we want to know about the organics in comets and why we think they might have a role to play in the origin of life is because we know from meteorites, which contain organics, that some of these organics are biologically interesting. They were probably made abiologically -- life didn't make them -- but they contain components like amino acids and a class of compounds called amphiphiles which, if you dunk them in water, will spontaneously form little membrane structures and so on.
There are organics present in meteorites that actually look like they could play functional roles in getting life started. And we can recreate those same kinds of compounds in the laboratory if we do things like blast cometary analogue ices with radiation. So there's some reason to believe that comets might in fact contain these same kinds of compounds, and so one of the things we want to do is look for these: do comets contain these biologically interesting compounds that could have played specific roles in getting life started?
Now, we haven't quite answered those questions yet but we do know the organics are there and we now these new organics at least are consistent with the kinds of stuff we make when we irradiate the ices. So it may well be that future studies will demonstrate that these things are present, and that's pretty exciting. I'm looking forward to delving into that one!
Jesse Carpenter: Scott, what future do you envision for the study of the sample return from the Stardust mission?
Scott Sandford: One of the things that's exciting about a sample return is that I can't even tell you now what we're going to learn from this sample. Its value -- I can give you a lower limit to its value because I've already gained value from it scientifically, but I don't know what's coming next. You know, the fact of the matter is some of the techniques that we used in the preliminary examination to study this sample did not exist when -- or were certainly not well-calibrated -- when we launched the spacecraft.
So I can't even tell you ten years from now what people will want to do with these samples. There will be analytical techniques available that I don't even know about, haven't even thought about. And so the things we can learn from these samples in the future -- who knows? I mean we can learn things to answer questions that we haven't even known we can pose yet, to some extent. And so the fact that we've learned so much already just tells me that this is going to be great. We're going to learn even more as time goes on. And, you know, after I've retired and I'm you know being pushed around in a wheelchair people will still be learning stuff from this sample. And hopefully I'll still be able to read the results, you know, so I'll learn more and more about comets as time goes on.
But I can't predict for you right now everything we're going to learn from this sample, because we'll be learning stuff from this sample in the year 2030.
Jesse Carpenter: In closing, do you have any reflections that you'd like to share with us about your experience with this project overall?
Scott Sandford: Yeah, I have to say I consider myself to be a really fortunate person. I mean, it's been a lot of work to do this mission and a lot of work by a lot of people -- not just me. But it has been a tremendous amount of fun to work with all these people. You know, there's a real marching army that you have to get together and move in the same direction to get a mission to go. But the thought that we could launch a spacecraft, go all the way out to this comet, capture samples -- even though they're moving at, you know, twenty times the speed of sound or whatever, relative to us -- bring them back to Earth, pry them out and study them is just amazing -- you know, to think that I've held a piece of a comet.
And I was on the recovery team so I was one of the folks who went out to Utah to collect it. And most of the time I was too busy to be very self-introspective about what was going on. We had a lot of things to do and we had to get them done right. But in the brief pauses, I have to admit to being sort of flabbergasted to think that here I am, participating with a group of people and in a larger organization that has done something sort of unique in the history of humankind, and that is to get a solid sample from outside the Earth/Moon system and bring it back to the Earth.
And so I think one thing that shouldn't be totally lost sight of – I'm in this for the science but in fact this activity, like many NASA activities, involves a bit of history as well. And I think people should keep that in mind. I feel very fortunate to be part of that and I also just want to acknowledge the fact that I was only a little part of that. I mean there were a lot of people working on this to make it work. And I enjoyed working with them, and you know I just can't wait to get onto the next sample return mission!
Jesse Carpenter: Thank you for joining us. I'm Jesse Carpenter and you've been listening to a podcast from the NASA Ames Research Center.
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