Planetary Radio: Space Exploration, Astronomy and Science - Deep Impact Begins to Reveal Comet Secrets

Episode Date: July 18, 2005

Deep Impact Begins to Reveal Comet SecretsLearn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Comet Tempel 1 Secrets Revealed by Deep Impact, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. The University of Maryland's Lucy McFadden is our happy but utterly swamped guest. I'm Matt Kaplan. and the team have figured out so far. Bruce Betts manages to mix Shakespeare, fish, and a new trivia contest in this week's What's Up segment. You'll just have to hang around to see what I mean. And while you're hanging, here's a handful of helpful headlines. Okay, this one is great.

Everybody knows gas giant planets can't possibly form in a three-star or trinary system, right? Except a Caltech astronomer has just found one, 149 light-years from Earth. Planets, planets everywhere, and a variable in the Drake equation bites a little more dust. Details are at planetary.org. While you're there, you can check out the latest cool images from Cassini, While you're there, you can check out the latest cool images from Cassini, the spacecraft whizzed by within just 170 kilometers, or barely 100 miles, from Saturn's icy moon Enceladus. Looks like it's going to be at least Saturday the 23rd

before Discovery can lift off on its return-to-flight mission. NASA engineers are still figuring out the problem with the fuel sensors in the big external tank attached to the space shuttle. What is a ring occultation? Here's a hint. It has nothing to do with that flawed cubic zirconia you bought your significant other. Let Emily help you figure it out. I'll be right back with Lucy McFadden. I'll be right back with Lucy McFadden. Hi, I'm Emily Lakdawalla with questions and answers.

A listener asked, what is a ring occultation? The Cassini spacecraft is now in a phase of its tour around Saturn in which it is performing experiments called occultations. To occult means to hide or conceal. Cassini's navigators are deliberately causing the spacecraft to travel behind Saturn's rings so that the spacecraft is hidden from the Earth's view. What possible use could hiding Cassini have for scientists? If Cassini were totally hidden from view in these experiments, there wouldn't be much use. But Saturn's rings are not solid objects. They are actually made of innumerable unconnected particles. Because of that, Saturn's rings allow some radiation to pass through them. During the spacecraft's passage behind the rings,

Cassini broadcasts a continuous radio signal which is picked up on the Earth. What can we learn from radio signals sent through Saturn's rings? Stay tuned to Planetary Radio to find out. Lucy McFadden has her hands full. She celebrated with the rest of us on the 4th of July as Deep Impact slammed into Comet Tempel 1. She watched in awe as the impactor portion of the spacecraft vaporized in a tremendous explosion, blasting tons of primordial dust and ice hundreds of kilometers into space. In fact, that explosion was even bigger than Lucy or her colleagues expected. It has made her job a little more challenging, but no less exciting.

We reached her at the University of Maryland, where she works as an associate research scientist in the astronomy department. As a spectroscopy expert and co-investigator on the Deep Impact mission, it's her job to figure out what all that comet stuff really is and what it can tell us about the early years of our solar system when Tempel 1 may have formed. Lucy, first of all, thank you for probably the most spectacular fireworks display in the history of the Fourth of July.

Well, I didn't do it alone. It was a big team effort, so it wasn't at something. And the team continues as you analyze, what, 4,500 images returned by the Deep Impact spacecraft, I guess both parts of it, and a lot of other data coming in from around the Earth. What have you learned so far? I've heard there are already some surprises. Well, actually, I'm overwhelmed. I'm glad to hear you tell me that there are 4,500

images, and that explains why I haven't looked through them all. We're just overwhelmed. We're trying to get ourselves organized here. What have we learned? Well, we learned that we made a big impact on this comet. We learned that the comet's continuing in its orbit, as expected. I mean, one thing that your colleague, Micah Hearn, the principal investigator, said is that you were surprised by the opacity of the stuff you knocked off of this comet. That did surprise us, and we're not quite sure why. Clearly, we produced a lot of stuff, why. Clearly, we produced a lot of stuff, and that stuff really saturated our detectors, filled our field of view, fogged us out at some point, and we weren't expecting that.

Although, of course we were expecting it. This was an experiment. So, you know, why should we be surprised that something unexpected happened? I mean, that's the way it is in an experimental science. Makes it more exciting, doesn't it? Absolutely. It's made it harder for us to find the creator. But, you know, we're still working on that. We do believe that all the dust that was sent out is very small, fine-grained, microscopic dust. And that's why it scattered a lot of light and that fogged our cameras or saturated our cameras.

Yeah, there's an image. I'm looking at one taken of the impact right now by the flyby portion of Deep Impact, and it is brilliant. I mean, it is just, it looks like it's lit from within, but I guess that's really reflected sunlight? Well, no, it depends on when you're looking. At impact, there was a lot of energy here. There was a lot of energy that hit the comet, and the impactor disintegrated.

That energy was turned into a shockwave, and for a brief time, the material was luminous. It was incandescent. It glowed. Real fireworks, yeah. So for a time it was self-luminous, but for a short period of time. And we're trying to figure out just how long that stayed luminous is something that will tell us something about the process. Well, your job, I guess, is spectroscopy.

And so with all this light, some of it actually generated by the explosion, some of it reflected sunlight. I suppose, I hope that means you have a lot to work with. Oh, yeah. Well, we have not only, we have tons of spectra which reflected sunlight, but also recorded fluorescent emission from the impact. So we have both emission spectra and reflected spectra, and we have the thermal background, too. So that gives us a wealth of data. And then our imager, the medium-resolution and high-resolution imager,

and the imager on the impactor, too, gave us great views of the comet nucleus, the closest views of the comet nucleus that have ever been recorded. So I really don't know where to begin. Do I look at the images before impact and look at the comet nucleus? Why would I do that? I should look at impact. I'm sitting here trying to figure out which way to turn. Well, fortunately, all this data is safely packed away on, I hope, a number of hard drives,

and you've got all the time in the world now, now that the impactor has been vaporized and did its job. Well, okay, thank you. Thank you again for telling me I've got all the time in the world. Oh, I know. Slight exaggeration. We are, again, making our plans and looking at the data. The first thing to do is to look at the data. Second thing to do is to verify that we've converted our raw signal, our digital counts,

our data numbers that we call them, we converted them into the right units of energy, and do we have the right corrections. So that's our first task, to make sure we can convert our measurements into something with physical meaning. And we're trying to figure out where the spectrometer was pointing. That's not an easy task to do. So we can take a concurrent image that was taken by the MRI and put the slit from the infrared spectrometer onto a visual image of the comet so we know what we're looking at, so we can interpret it.

And when you talk about a slit, I mean, obviously this very advanced instrument works like spectrometers have since they were invented. You have the light coming through the slit and you look at the spread of the spectrum that emerges from it. That's true. That is a principle that has been known for hundreds of years, probably 150 or so. The advantage that we have acquired in recent decades is that we have these detectors that are two-dimensional, so they're arrays, so that we can get a spectrum in the wavelength dimension as well as a spectrum in the spatial dimension. So we have an image cube.

We have a three-dimensional data set. It's quite rich, but it's a challenge to work with. I can imagine. You know what it's like? It's like looking at the images, learning how to deal with the images is like learning how to play a piano. An imaging spectrometer is like learning how to play the organ. An organ is just a much more complicated instrument.

With your feet going and several, yeah, I understand. Different octaves and everything. So it can be done, but boy, it's a challenge. everything. So it can be done, but boy, it's a challenge. Well, hopefully you are all learning to make beautiful music there as we head into a time when we need to take a quick break. But there's a lot more I'd like to ask you about Deep Impact and what you've learned about Temple One, and also more about that crater, which it's so difficult to see because, of course, there are, oh, a few people out there who are anxious to hear how big that thing is to see who won that prize. Right.

We'll come back and do that in a moment, if that's okay. Our guest is Lucy McFadden. She is an associate research scientist at the University of Maryland in the astronomy department. But more important for purposes of this conversation and what she's probably spending most of her days and nights doing, she is co-investigator on the Deep Impact mission. And we'll be back with Lucy right after this. This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary Society,

the world's largest space interest group. The Planetary Society is helping to explore Mars. We're tracking near-Earth asteroids and comets. We sponsor the search for life on other worlds, and we're building the first-ever solar sail. We didn't just build it. We attempted to put that first solar sail in orbit, and we're going to try again. You can read about all our exciting projects

and get the latest space exploration news in-depth at the Society's exciting and informative website, planetary.org. You can also preview our full-color magazine, The Planetary Report. It's just one of our many member benefits. Want to learn more? Call us at 1-877-PLANETS. That's toll-free, 1-877-752-6387. The Planetary Society, exploring new worlds. Lucy McFadden is our guest on Planetary Radio this week.

She is one of that team that provided that tremendous fireworks show, one with great impact. Just before the 4th of July, for those of us on the West Coast, but for most of the world, it was smack dab on July 4th. And it was smack dab on Comet Tempel 1, which got a rude awakening early that morning when a little over 800 pounds of copper slammed into it at something like 23,000 miles per hour. Lucy, we were talking about spectroscopy. As all that dust was coming off, what did you learn or what have you learned so far from these spectroscopes that were looking at the impact? Well, so far we've only looked at

the very few seconds after impact. So we've looked at a small subset of the data. But that's the most exciting part to have looked at. And we see emission lines due to very hot water, very hot carbon dioxide, and hot hydrocarbons. Was any of this a surprise? Not necessarily. These are what we expected. We designed the spectrometer to see these features. What surprised me, though, you know, I was glad to see these emission bands due to very highly ionized and excited electrons in these basic components that make up all comets. But what surprised me was I was expecting more complicated chemical reactions to occur

at the time of the impact when things were very hot. And that surprised me. I thought we'd see spectra with lots and lots of lines that we couldn't interpret and that the thing would look like chicken scratches all over the place or just scribbling by a little kid. I was surprised and relieved to see the bands, the emission bands, in regions that we could understand and interpret and that they were well-defined and there wasn't a lot of chemical reactions. So that's something I learned.

Now, maybe people with a chemical background could have predicted that, that the hot flash was very short-lived. There really wasn't a lot of time for a lot of complex chemical reactions, and that this impulse of the impact was just a short impulse, and it really just propelled the material out of the comet. Do you suspect that we are going to learn from this data and these images that comets are not just knockoffs of each other, clones, that they may be a little bit more individual than we thought?

Yeah, probably. The striking thing to us when we saw the nucleus at close range was that there were features there that we hadn't seen yet on other comets. Remember, we flew past Comet Halley in 1986. We flew past Comet Borelli in 2001. And then last January, we flew past Vilt 2, another comet. They all look different. They're all made of the same things, but their surface morphology differs. And this is probably telling us something about their history in the solar system.

Comet Halley has an elongated, very elliptical orbit, a longer period of about 76 years, I guess. And so it's spent its time in different parts of the solar system. Tempel 1 has circular features on them that you might call craters. They appear to have raised rims. But some of my science team colleagues say, oh, be careful here. We're talking about an icy body where sublimation is the dominant process, and you can't tell yet whether these

circular features that have well-defined and raised rims were formed by impacts that have sustained throughout the lifetime of the comet, or even sustained since they hit. Well, at least you know one of them was made by an impact. That's right, exactly.

But that one's proving hard to find. We know where to look for it, but we haven't seen it yet. Well, what can we say then, with a couple of minutes left, to those people who are waiting with bated breath to find out who came closest to guessing the diameter? I have to say, please be patient. What we did, we know where to look. We went and looked, and we thought we found something, but then we said,

nope, this isn't the crater. This is an artifact of our image processing. And then we determined with further analysis, this was a great team effort, we determined that we needed to get better calibrations. We needed to know our background better, and we actually went back to the spacecraft this last week and took some more calibration data. And it's going to take us another week or two to process that.

We just got the data next week or the week, and then in the next two weeks we're going to be working on it, so we have to ask for patience. And believe me, we all want to find it too, because many of us have a bet on it too. That doesn't seem fair. You can't run into the contest, but I can understand where you... We didn't enter the planetary contest, but that doesn't mean that we don't have our own contest.

Yeah, I don't blame you. Well, I do blame us because it's making it hard for us to be objective. Yeah, well, I'm sure you'll act like responsible scientists. Well, I didn't bet in this thing, and I couldn't figure out why until I heard everybody say, oh, I'm sure it's going to be 156 meters, right? And then I realized everybody had their favorite number. So I think I'm going to be the one that will make the measurement, because I couldn't bet on this. So I'll be the official measurer, because there's nothing at stake in it for me.

Yeah, thank goodness you can be the objective referee. We only have about a minute left. What happens now over the next weeks and months in your life and with that part of Deep Impact that is still very much a functioning spacecraft? Well, you know, we did get permission from NASA headquarters to make a final trajectory correction maneuver, a TCM, make a final trajectory correction maneuver, a TCM, that's going to place the spacecraft in an orbit that will allow us to wake it up later should we determine that we have another comet to fly by.

So NASA has not approved an extended mission, but they have approved us to put it in a parking orbit that gives us the option in the future, after we have some review of our plans, to possibly fly by another comet. So deep impact, the story may not be over, and it certainly is not over in terms of the conclusions that you may be able to reach from all that data. Oh, absolutely. We're just starting. Okay, a word now about that party that followed at JPL. Were you there to hear the Comets?

You bet. We danced to the Comets. Rocked around the clock. Bill Haley's Comets. Yes, it was terrific. It was a wonderful event, a great way to celebrate the impact, and boy, are the Comets ever good. Lucy McFadden has been our guest. She is an associate research scientist at the University of Maryland,

where she works with Michael Ahern, and both of them will most recent developments in the Deep Impact mission. And, of course, we will put up the links to both the JPL and University of Maryland websites revolving around Deep Impact. Lucy, anywhere else people should look? Matt, I just wanted to let you know that the Discovery Channel has done a documentary, an hour-long documentary that will air on July 31st, 10 p.m. Eastern and Pacific time. And for times in between, have to check your local listings. Excellent. That's great. Lucy, we're about out of time. I'm going to thank you and wish you the best of luck as you continue to analyze that data from Deep Impact. And nobody's rocked both the astronomy community and Comet Temple 1 quite as well as the Deep Impact team. We'll be back with Emily Lakdawalla and a little more of her Q&A segment for this week,

followed by Bruce Betts with What's Up. Thanks, Matt. I'm Emily Lakdawalla, back with Q&A. In a ring occultation experiment, the Cassini spacecraft flies behind Saturn's rings as seen from Earth while broadcasting a continuous signal. That signal is picked up by Earth-based ground stations, which record how the strength of the signal varies with time. As Cassini passes behind a ringlet with more particles, the signal strength decreases. Then it passes behind a gap and the signal strength increases. When the signal strength is turned into a map of Cassini's course,

a picture emerges of the density structure of the rings. The resolution of Cassini's map of the rings is limited only by the accuracy of the clocks at the ground stations. Ring occultation experiments could reveal structures only 50 meters wide, one ten-thousandth of one percent of the width of the rings. What's even more tricky, Cassini can broadcast its signals in three different radio wavelengths. Radio waves don't interact with particles that are smaller than their wavelength. So if rings contain particles smaller than a few centimeters in size, they could be transparent to one radio wavelength, but not another.

The Cassini ring occultation experiments will yield incredibly detailed knowledge of the fine structure of Saturn's rings and the size of the particles they are made of. But what creates all those fine divisions and ringlets? Scientists have yet to figure that out. Got a question about the universe? Send it to us at planetaryradio at planetary dot org. And now here's Matt with more Planetary Radio. Well, I don't know how well you can hear it, but you probably can tell that What's Up is on location again with Dr. Bruce Betts, the Director of Projects for the Planetary Society. Hi, Bruce. Where are we?

We are in Long Beach at the Aquarium of the Pacific and also at the Shakespeare Festival. And there's good reason for that. Now, you were actually just down here with your boys because they're sitting with us, and we may or may not hear from them later, but it also happens to be the location of the Long Beach Shakespeare Festival, the second year that they've done it out on the grass

in front of the aquarium. And my daughter is in this production of The Tempest. It's her last show, so it's a good place to be. Aww. Yeah, so it's a good place to be. Aww. Yeah, so it's child evening in planetary land. On this planet. On this planet. Let's talk about what other planets you can easily see in the evening sky.

Don't miss the Venus and Jupiter show these days. Look low in the west, and the really, really bright star-like object is Venus. Look above that a ways, and the other bright star-like object is Venus. Look above that a ways. And the other bright star-like object, a little bit dimmer, is Jupiter. And in the pre-dawn sky, you can see Mars in the southeast getting brighter and brighter for the next two or three months. Good stuff. On to random space fact! Jupiter's moon, Europa, is thought to have a subsurface ocean. I thought this appropriate outside the Aquarium of the Pacific,

under a few kilometers to tens of kilometers of ice, and it gets people very excited in the astrobiology world because of the presence of liquid water. And it exists because of the tidal interactions between Jupiter and Europa, but also requiring the moons such as Io and Ganymede to tug each other around, the same reason you get lots of volcanism on Io. I don't know. Renaissance music and oceans on Europa? Why not? We shall sail the seas, exploring as the new dawning, the awakening of the...

Okay, whatever. Anyway, on to our trivia contest. Last time we asked you why the shields that protected the Deep Impact spacecraft as it flew through the coma or dust of the comet, why those are called the Whipple Shields. Who are those named after? How did we do, Matt? Lots of new listeners.

I don't know if this is because we're picking up so many other radio stations or what, but all kinds of names that I had never seen before. Here's one that you might almost recognize, Bruce. We got an entry from Stephen Hawkins. Sorry. Stephen Hawkins wrote in from Boone, Iowa. I just had to play with the name there because wouldn't that be cool? But no, it wasn't Stephen Hawking. It was Stephen Hawkins. He also was not our winner. Our winner was actually chosen by one of your boys.

You ready for that? I am. So basically, you just read poor Stephen Hawkins' name to get a little bit of humor out of it. Yeah, did I get a little bit? A little bit. We actually do appreciate your entry, however. I just want to make sure everyone knows that. But you didn't win. Who was randomly selected by my son? Chris Lewis of Lafayette, Colorado had the right answer.

The Whipple Shield is named for Fred Whipple. Indeed, Fred Whipple, a long-term planetary scientist who was the originator of the dirty snowball model of comets and such. So named after Fred Whipple. One of the listeners wrote in, actually a couple of them, and said that Fred Whipple actually invented the Whipple shield in the 40s before we had sent anything out into space. Yes, it was actually to take care of bugs off the front of your car as you're driving around on the freeway. Yeah, what have you got for us next week? Well, next week I take you back to Europa and its subsurface ocean.

Asking you why, or I'm sorry, what evidence, give me one piece of evidence we have for Europa having a subsurface ocean, something that's not totally confirmed, but we do have at least a couple really good pieces of evidence. Give us at least one of those and send your entry to us via planetary.org slash radio, where you can find out how to email us. And, you know, just a little bit, a few words is adequate, as long as they're the right words. And get those entries to us by Monday, July 25th at 2 p.m. Pacific time, the 25th at 2 p.m. Pacific,

so that your entry in this week's or this brand new trivia contest on What's Up will have a chance at winning another Planetary Radio t-shirt, just like Chris Lewis. Bruce, I think we're done. All right, everybody, go out there, look on the night sky, and think about... Think about... I have no idea what... Wait, Kevin, what should they think about? Shoes.

Shoes. Daniel, what do you think they should think about? Alien sharks. Alien sharks. Very nice. Alright, everyone, go out there, look on the night sky, think about shoes and alien sharks. Thank you, and good night.

That's Bruce Betts and boys with What's Up? Comes to us every week here at the end of Planetary Radio. Bruce Betts is the director of projects for the Planetary Society in Pasadena, California. And we say good night from the Long Beach Aquarium of the Pacific, where we are finishing the Renaissance music, and they go out with the Temp Aquarium of the Pacific, where we are finishing the Renaissance music and they go out with the Tempest. By the way, if you're in Southern California, drop on down and see Henry V over the next four weekends. We're almost done for this week, but we have a favor to ask.

Bear with me as I explain. We know of 20 or 25 radio stations that air planetary radio. Some of them get the show each week from National Public Radio's Public Radio Satellite Service. The nice folks there take very good care of us, but they have no way to identify every radio station that receives the show. And we think there may be a few out there that haven't gotten around to telling us. That's where you come in. If you're listening to us on your local station, could you let us know?

Just send the station's call letters and the time it airs Planetary Radio to our email address, planetaryradio at planetary dot org. Don't worry, we don't want to yell at them. We just want to let other people know where to tune in. Sorry, no prizes for this, but you'll have our eternal gratitude and the knowledge that you are a citizen of the solar system in good standing. Come on back next time to hear four-time shuttle astronaut Tom Jones talk about his new book, The Complete Idiot's Guide to NASA. Thanks for listening, everyone, and have a great week.