Planetary Radio: Space Exploration, Astronomy and Science - Europe's Rosetta On Its Way to a Comet

Episode Date: March 12, 2007

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landing on a comet this week on planetary radio hi everyone welcome to public radio's travel show that takes you to the final frontier i'm matt caplan rosetta visited mars just two weeks ago. It's one of many whistle stops on a 10-year, four-and-a-half-billion-mile journey to a comet. This week, we'll meet the mission's project scientist. Gerhard Schwemm will tell us about that very successful swing past the red planet and where Rosetta goes from here. Emily Lakdawalla has found the heartbeat of Saturn. She'll play it back for us during her Q&A segment, and she'll tell us what that rhythm is telling scientists about the ringed planet.

Bruce Betts has a tale to tell about the night sky, culminating in another chance to win the coveted and highly fashionable spring edition of the Planetary Radio T-shirt. It's a busy show, and we only have time for a few space headlines, beginning with bad news for anyone who'd like to find near-Earth objects before they find us. The U.S. Congress asked NASA to come up with a plan to find the 20,000 or so biggest killer asteroids, but they haven't come up with the money to pay for the search. On the other hand, the Planetary Society has just named the latest winners of Shoemaker-Neo grants.

The seven researchers in five countries will use the funds to aid their searches for the rock with our address stamped on it. Both stories

are at planetary.org where you'll also find Emily's blog. She writes about one place on Earth that still considers Pluto a planet. The New Mexico

State Legislature has issued that declaration, at least when Pluto is in the sky over the southwestern state. And here's Emily with that Q&A. Gerhard Schwemm is just a minute away. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, what does the length of a day mean for a rotating ball of gas like Jupiter? New Horizons and several previous missions have returned animations of Jupiter's clouds,

showing that each dark belt and light zone seems to be moving around the planet at a different rate, with the anticyclonic storms rolling in between them. moving around the planet at a different rate, with the anticyclonic storms rolling in between them. It's obvious even through a backyard telescope that the whole planet rotates under these clouds, but how do you pick the length of one day when there are no surface features to set Jupiter's equivalent of the Greenwich Meridian? What you need is some signal from Jupiter's rotating interior that is not subject to the same variability as its upper-level clouds. Fortunately, Jupiter and the other gas giants do send signals from their interiors that scientists can tune into. Stay tuned to Planetary Radio to find out more.

Gerhard Schvame has already been working on Rosetta for more than two decades, and it will be another seven years before his spacecraft begins orbiting 67P Churyumov-Gerasimenko. Good thing he has lots to keep him busy, including two asteroid flybys and two more visits to the mysterious planet known as Earth. The missions project scientist is also head of the Solar System Science Operations Division for ESTEC, the European Space Research and Technology Center at the European Space Agency. In fact, he was ESA's first planetary scientist. Thanks so much for taking some time out on a Saturday to bring us up to date on the Rosetta mission. Let's begin with this very successful flyby of Mars that your spacecraft just experienced.

I take it that everything went extremely well. Yeah, that's correct. Everything went extremely well. And for us, it was really the first major step on the long route to the comet after the launch because we had to use the Mars gravity assist to really retarget the spacecraft very precisely to Earth for our next Gravity Assist with a much bigger body, which is really important that we then gain the orbital energy to make our way to Comet Chirium of Karasimenko.

It's very interesting, and I think this may come up again in our conversation, that there are parallels between your mission, Rosetta, and the New Horizons mission. We were covering its flyby of Jupiter just last week, and I read, in fact, that some of Rosetta's operations were coordinated with the New Horizons flyby. Yeah, this is correct. We have the good chance that we can do measurements together with New Horizons. New Horizons passed Jupiter on the 28th. We have one instrument on board from our orbiter payload, which is Alice, a UV spectrometer.

The PI is Alan Stern, and Alan Stern, as your listeners who have listened to you know, is also the PI of the New Horizons mission, and it was a good opportunity to then coordinate observations of Jupiter from both spacecraft from different viewing angles, so to say. And as I said, I think some of these other parallels may come out later in our conversation, but let's come back to Mars. You had one image in particular very near your closest point to Mars.

A lot of us here, and particularly I think my colleague Emily Lactawala, were particularly enamored of. And that was this shot from one of your instruments that actually caught a bit of one of your solar panels. Yeah, this was an amazing image, and I was really glad that we got this excellent shot. And it also gives you a great feel, you know, from a flyby, because you see, you get a perspective. You see part of the spacecraft. You see Mars below. It's like you sit in an aircraft and look down on Earth. At closest approach, we had to switch off most of the orbiter subsystems and also the payload

because we went through an eclipse. And Rosetta is not designed to go through this eclipse. It's now en route to the comet. And OSETA is not designed to go through this eclipses now en route to the comet. But the lander who will be deployed onto the comet Nucleus has to live on his own power there. So what we did, we charged the lander batteries, and then the lander was, so to say, taken as a standalone instrument and could run on its own power. run on its own power. So the lander camera, the SEVA camera, was able to take this close-up picture basically from 250, 300 kilometers high above the surface. This lander has really a historic role to play once you reach the comet, which is Rosetta's ultimate goal, because it will be the first spacecraft to set foot on the core of a comet,

the inner ice ball or dirty snowball, as we've come to know comets to be. Yes, that's really one of the highlights of the mission today, and it will happen very early in the comet science phase that we have, that we put and deploy the lander, and it should soft land onto the nucleus, anchor onto the nucleus, and then take in situ measurements. This will be one of the very important parts of the mission, and we're also glad that, again, two instruments really demonstrated how good they work, so the SEWA camera, and we also got some very good measurements from the instrument that's called ROMAP,

which is the plasma instrument and a magnetometer. So although there we got very good data. We have not yet got the data analyzed. We should get the results in a couple of days, I hope. They are working on it. But then you can also intercalibrate the two instruments, and you can also compare itibrate the two instruments, and you can also compare it to previous measurements around Mars.

However, there you have to say there are not so many plasma instruments that are flying around Mars. We were a little bit alone in that area, but we got excellent data, and we can also see we have Mars Express there, another ESA mission that is orbiting Mars, where we have a plasma instrument. And this will help us to calibrate our instruments, as you say. And it was a great opportunity, and we got, I believe, also good science out of it. Yeah, in fact, that's the next point I was going to make.

This was more than a flyby and a chance to test your instruments. You really did conduct science at Mars. Yeah, this is correct. This was, for us, was secondary, I really have to admit. But we took the opportunity, and it turned out that we, I think, did a pretty good job to really introduce a very nice timeline for these instruments. And as you saw from this Lenda instrument, a great shot, which is just by its beauty, so to say.

You don't have to make science out of it. It's just a wonderful sight of Mars with a spacecraft, basically, on the image. But also the OSIRIS camera, this is our imaging system on the orbiter, really took a few brilliant shots of Mars and also could, in the different wavelength areas that camera has, which are basically unique for an imaging system because it's designed for comet. But there you could also look for, you know, certain molecular lines. We have this wonderful image where you see the clouds up above the Mars surface. So the data are there,

and as usual, my colleagues have to work on this data. We will put links to your website and some of these images, of course, on our website, right where some people are probably listening to this program, but if you're not, they'll be at planetary.org. We encourage people to take a look. There really are some spectacular photos. Rosetta is on, like New Horizons, an extraordinarily long trip. I like to think of it as two round trips to Saturn, except that you have some additional flybys ahead of you.

Yes, that's correct. We will now go to the Earth, as I said, for gravity assist. That will bring us, so to say, a little bit farther away from the Sun, so we will have our first asteroid close flyby in 2008, come back to the Earth for another gravity assist, then go to asteroid or flyby asteroid Lutetia a couple of thousand kilometers distance. And then we come into another very critical phase for us where we hibernate the spacecraft because we are far away from the sun and we have not enough power to run the spacecraft fully fledged. So we will put in hibernation for about two years. we have not enough power to run the spacecraft fully fledged. So we will put in hibernation for about two years,

and when we come out of this hibernation, then the really exciting cometary science will start. So beginning of 2014, when we wake up the spacecraft again and prepare ourselves for rendezvous with the cometarium of Gerasimenko. We should see, so to say, the comet in spring, and then we have what we call an observation phase, a mapping phase, because we have to characterize the comet nucleus and to prepare for the lander deployment. And this lander deployment we want to do at the end, late autumn in 2014.

So this 2014 will be a really exciting time because we will, so to say, get close to the nucleus, prepare everything to go into orbit and learn as much about, so to say, the dynamics of the nucleus that we can prepare. And this will be a very intensive phase. that we can prepare. And this will be a very intensive phase. We have three and a half months for characterizing the nucleus because we also have to find a nice spot where we want to land, an interesting spot, to program everything correctly that we can deploy the land. I can tell you this will be very, very exciting.

We are looking forward to it. We still have to be patient. We still have to do a lot of work to prepare. I'll be right back with more from Gerhard Schvehm of the Rosetta Comet Mission. We are looking forward to it. We still have to be patient. We still have to do a lot of work to prepare. I'll be right back with more from Gerhard Schvaym of the Rosetta Comet Mission. This is Planetary Radio. I'm Robert Picardo. I traveled across the galaxy as the doctor in Star Trek Voyager.

Then I joined the Planetary Society to become part of the real adventure of space exploration. The Society fights for missions that unveil the secrets of the solar system. Transcription by CastingWords of this greatest of all voyages, and I hope you'll consider joining us. You can learn more about the Planetary Society at our website, planetary.org slash radio, or by calling 1-800-9-WORLDS. Planetary Radio listeners who aren't yet members can join and receive a Planetary Radio T-shirt. Our nearly 100,000 members receive the internationally acclaimed Planetary Report magazine. That's planetary.org slash radio.

The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. We're talking with Gerhard Schwemm, project scientist for the European Space Agency's Rosetta mission, the first ever to orbit and even land on a comet. But do you really land on something that's only four kilometers in diameter? Now, with an object this small, is it actually a landing, or is it more like a rendezvous? No, it's actually, yeah, it's a touchdown, it's a landing.

But, you know, one of my colleagues, he wants that, and that comes close, that this is a mission to kiss a comet. You go very smoothly, you know, very gently down there, and you basically fall onto the surface. We are in orbit around the nucleus, and then we deploy the lander that we give him, so to say, in a small velocity against the orbital velocity we have for the nucleus. That means it will then gently fall down. And this has to be really timed and designed very, very carefully and accurately. I give you now rough numbers because this is what we have in the planning and the requirements

from about two kilometers above the surface. And then it goes down with about 30 centimeters per second. So it's very gentle. Yes. But on the other hand, you'll be orbiting something, well, at times as close as 2 kilometers from the comet's head. Will Rosetta be passing through the tail of the comet, and are there any concerns about damage from material coming off of the comet?

We are sitting so close with the spacecraft that we are in the coma. Wow. The tail is far. This is one of the things are in the coma. You know, the tail is far. This is one of the things some of the guys want to go. But we are at two kilometers distance from the surface. Basically, if you look at it from perspective from Earth, we are

close to the nucleus. The tail is farther away. You know, the coma extends several 10,000 kilometers. It depends how active the comet is. But when we arrive at the comet, and this is the phase why we want to deploy the land also very early we arrive at the comet at a very inactive time so to say we are still far away from the sun the other thing is where always people are so to say concerned about and that one has to say as well this is a rendezvous mission you know even stardust when it collected the samples,

it was basically relative velocity was 6 kilometers per second. Yes, yeah, huge. Yeah? So this is 6. What we do is meters per second, relative velocity with the dust. Yeah? So up to 200 meters per second depends what orbits we chose as we get there. So you have to see these are totally different domains.

So the threat is much less than stardust. Yeah, no, the threat is really low. What we have to look at after or have to be careful with is later when, you know, we stay with the comet when it goes through its perihelion. Yes. So we have to be very careful to really monitor how the production of how the comet releases

dust and gas and that will increase when we get closer to the sun and the more danger you have is that you collect dust on surfaces. From the studies we have we are fairly confident and I can tell you just as an example, we have

instruments on board that have to collect dust. This is, you know, the COSIMA instrument, which is a dust mass spectrometer, that has to collect dust on the target. And also MEDUS, which is an atomic force microscope, they have to collect. And we have in our preliminary planning, we have to put in, so to say, two or three weeks where we give these instruments really the opportunity to collect. It takes a lot of time to collect enough dust. I should think that as Rosetta approaches the sun and becomes more active, that this will become a much more exciting time for Rosetta and for your scientists to be watching this for the first time from this kind of distance.

Yeah, sure. This is one of the prime objectives as well. When we go with Churyumov-Gerasimenko, when we get to the sun, we want to see how the production rates of the comet increase. We want to understand how this sublimation of the frozen gases works. And I can tell you this will be really an exciting time. And I believe we will basically in real time, we will learn a lot of new things. What else do you hope that Rosetta will help us to learn about comets and in particular the nucleus of a comet? I think one of the prime objectives we have, and I think that we will learn a lot because we have a very good payload for this, is the composition of the comet,

and especially the composition of the volatiles, the frozen gases that have been released. The second problem we hopefully get a handle on is the density of the comet. We believe that everything there is very fluffy, but we want to see how the gases or the ice and the dust, how that is there together, in what structure you will find it. So all these questions come, you know, come to mind, they have to be answered. The third one is really what we just addressed, is, you know, how does this sublimation really work? How is a comet working when it's heated up?

And we have, from the orbiter, we really have high-resolution imaging. We'll get down to a few centimeters. So I hope that we get a prime view of sublimation going on. Dr. Schwemm, you've already been on this mission for over 20 years. I've read that you became lead scientist for Rosetta in 1985. No, I was a study scientist at that time, but, yeah, I was leading the science team. It was in the really early, early stages, yeah. But with the mission for 22 years, and you've got seven more to go.

That's a long time to spend on a mission. This is correct, but I also have to say that I'm slowly phasing out. You know, one thing is that I, since a couple of years, am already doing much more management work than I did before. But secondly, this is perhaps for those listening to you in the U.S., we have still these rules that we have at a certain time. We have to go into pension. We have to retire from our job. And perhaps have more time again to go back to science and really do something with the data that we will get from Churyumov-Gerasimenko.

Well, I certainly hope that that's exactly how your life proceeds and that you continue to see the kind of success that we are seeing from Rosetta, and particularly as it nears that comet nucleus in 2014 and will be very active there, hopefully until well into 2015, during, interestingly enough, the same period that New Horizons flies past Pluto. Yeah, I think the whole community is really looking forward to these two exciting years. Well, I'd like to think that we could check back with you again, perhaps for the first of those asteroid flybys that you mentioned earlier in our conversation.

Yeah, you're welcome. I think it's always a good opportunity for us also to get a little bit of the excitement across and to demonstrate and explain what we are doing. Thank you so much. I think you've done that very well, and thanks for joining us. Thank you very much. Dr. Gerhard Schwemm is with ESTEC, ESA-ESTEC, ESTEC being the European Space Research and Technology Center.

ESA-STEC, STEC being the European Space Research and Technology Center. ESA, of course, the European Space Agency, from which we have stories quite frequently nowadays. He is, in addition to being the project scientist for Rosetta, he is the head of the Solar System Science Operations Division. We'll be speaking with Bruce Betts for this week's edition of What's Up, right after this return visit from Emily. I'm Emily Lakdawalla, back with Q&A. How do we figure out the length of a day on a gas giant when there's no solid surface that we can watch rotate? The answer is that scientists don't watch, they listen. The

giant planets all broadcast on radio frequencies. These radio emissions come from charged particles interacting with the magnetic field. The magnetic field is generated deep in the interior of a planet, so as the whole planet rotates, so does the magnetic field, and consequently so do its radio emissions. Here's the sound of Saturn rotating, sped up so that one second equals one Saturn day. According to measurements by Cassini, one Saturn day is about 10 hours and 46 minutes long. But therein lies a puzzle. Voyager performed exactly the same measurement and got a rotation rate more than 6 minutes shorter than the Cassini rotation rate.

This cannot actually mean that Saturn has slowed down that much in 20 years. There is no physical way for Saturn to have given up so much angular momentum so quickly. So it seems that although the radio rotation rate gives some clues, there are still a lot of puzzles concerning what's going on deep inside the giant planets. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Time for What's Up on Planetary Radio.

Bruce Betts is the Director of Projects for the Planetary Society. He is ready once again to tell us about the wonders of the night sky. Go out, look around, find the stuff he talks about right now. It's wonderful. And first, the wonder of the daytime sky. Partial solar eclipse March 19th from eastern Asia and northern Alaska. Road trip. It's never too late.

Well, unless you're listening to this the day after. I'm up for it. I'm ready. Let's go. Let's blow this joint. Really? Yeah. You and me? Yeah.

Road trip. Who else? Northern Alaska. I'm ready. I'm going to go. As long as I get some northern lights in. Well, it's a good time for them. All right.

Okay. Okay. Yeah, okay. We'll see. All right. It's getting really boring for the listeners, so let's tell you what else is up. We've got in the evening sky, Venus just always dominating there in the west, shortly after sunset in the early evening.

That really, really bright looking star-like object, that's Venus. We've also got Saturn high in the sky in the early evening, looking kind of yellowish, sort of near Regulus, a bright star. And in the pre-dawn sky, we've got Jupiter high over, high up in the sky, looking like the brightest star-like object up there at that time. And Mars lower in the southeast during dawn. And if you really try, you might pick up Mercury, which is briefly going to be above the east-southeast horizon, well to the lower left of Mars. Busy sky.

Yeah. I'm exhausted. On to this week in space history, 1781. William Herschel discovered Uranus during this time period. Which is a nice consolation. You know, England losing America and all that. They found a planet. We'll colonize that place.

Well, there's the whole naming thing. They were going to name it after King George. Oh, that's right, yeah. But eventually it changed to the much more popular and much more maligned Uranus. Really? There would have gone a lot of junior high humor between then and now.

Yeah, if they called it, like, Georgian, that would have been different. 1926, Robert Goddard launched the first liquid-fueled rocket. One of my heroes. The rocket, or? No, Robert. Oh, okay, yeah. No, he's worthy of hero-tum. Hero-tum? Yeah. One of my heroes. The rocket or? No, Robert. Okay, yeah. No, he's worthy of hero-tum.

Hero-wishes. Hero-tum? Yeah. Hero-tum, I always count. He's hero-wishes. On to Brandon's first fact! Hey, did you know that Voyager 2 was launched before Voyager 1? Kind of crazy, huh?

It was, no, not a lot different, but about two weeks before Voyager 1 in 1977. But Voyager 1 was on a faster trajectory and so got to Jupiter first and Saturn first, hence the 1 designation. And they knew that was going to happen. Yeah, it was just a surprise. Whoa, we better change the numbers. Yes. Well, they have trouble with numbers sometimes, you know, putting things in backwards and so on.

So they might have put the wrong spacecraft on the rocket. Yeah. Yeah, that's what they did. Moving right along to the trivia contest, we asked you, what is the diameter of the New Horizons radio antenna? How'd we do? This one is so cool because what happened was, now before we get to the winner, we have to mention Craig Journet, who noticed that there were different numbers on different websites, even on different NASA

websites. And he found that the general answer was one thing, but one particular website at the National Space Science Data Center at Goddard said that it was 2.5 meters. And he wrote to them and pointed this out, and they said, oops, thank you for letting us know. We've had it wrong. Witness the power of planetary radio listeners. Truly. Isn't that cool?

That's pretty cool. You want to know who really won, though? I do. Who was the randomly selected one who said 2.1 meters? That's what she said, Colleen Keneally. And she said it in Eden Prairie, Minnesota. Colleen, congratulations. We're going to send you out a planetary radio T-shirt.

And it is amazing, isn't it? 2.1 meters, and we're going to be talking to it from Pluto. Yeah, that's really far away. Yeah. Did you know? I did. Yeah, okay. And further, I mean, it's going to keep it up, right?

Yes, that's really the goal, and they have every intent to encounter a Kuiper belt object. Never ceases to amaze me. It is pretty amazing stuff. Let's ask you another trivia question to give more of you an opportunity to win your Planetary Radio t-shirt. Scientists from what country have provided magnets for nearly all the recent and future Mars missions, including the Mars Exploration Rovers and the Phoenix mission? Who provided the magnets that sit there and collect the Martian dust? What country are the scientists from?

Go to planetary.org slash radio. Find out how to send us your answer. And you've got until Monday, the 19th of March at 2 p.m. Pacific time to get us that answer. Are we done? We are. Okay, everybody go out there, look on the night sky, and think about flying corks. Thank you, and good night. Flying corks?

Flying corks. Okay, I'm going night. Flying corks? Flying corks. Okay, I'm going to ignore that and throw out a rhetorical question. Why are we able to pick up excellent data from beyond Pluto, from this tiny transmitter on a 2.1 meter dish, and my cable reception sucks?

You said it was rhetorical. You're right. You're right. You're right. If you paid as much for your cable reception as they paid for their mission, you probably would have excellent cable. Couldn't the Deep Space Network go into television distribution? I mean, they might pick up a few extra bucks. Yeah.

As long as they can keep track of which spacecraft number they put in which rocket. Bruce Fetz is the director of projects for the Planetary Society, and he has to put up with an awful lot sometimes when he joins us here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week, everyone. Thank you.