Planetary Radio: Space Exploration, Astronomy and Science - Ion Engines Drive Dawn to Asteroids Vesta and Ceres

Episode Date: December 24, 2007

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Sailing to the solar system's most massive asteroids, 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. As we speak, a little spaceship with great big wings is flying toward a big rock called Vesta. It will stick around a while once it gets there and then leave for an even bigger world called Ceres. After that, who knows where Dawn might head.

Not even Principal Investigator Chris Russell is entirely sure. Chris will join us today to talk about this first-ever mission that will orbit two different bodies, driven by the steady thrust of its ion engines. We'll also hear from Emily Lakdawalla about whether New Horizons had to be the first probe to visit Pluto. Could one of the Voyagers have been directed there? And we'll wrap up this holiday edition of our show by letting Bruce Betts once again play Santa Claus. And we'll wrap up this holiday edition of our show by letting Bruce Betts once again play Santa Claus. He'll tell us what to watch for in the crowded night sky and send a Planetary Radio t-shirt down someone's chimney.

2007 has been one of the busiest and most productive years ever for space exploration, with spacecraft headed almost everywhere from Mercury to Pluto. Unfortunately, our lead story this week is about an all-too-Earthbound problem for an upcoming mission to Mars. NASA says a conflict of interest discovered within a panel of experts must be resolved before the winning candidate for the Mars Scout Program can be selected. And since Mars missions launch during a window that only opens up every 26 months, it will be 2013, not 2011, before this trip to sample the

red planet's upper atmosphere gets underway. You can learn the details in Emily's blog at planetary.org. Speaking of Mars, somebody should warn the Martians to watch for falling rocks. It's just possible that the planet will take a moderate pasting from an asteroid called 2007 WD-5. Only discovered a month ago, the 50-meter-wide projectile is being watched carefully. My colleague Amir Alexander reports that there is about a 1 in 75 chance of impact on January 30. Those odds will change as astronomers learn more about the asteroid's path. Check out Amir's article at Planetary.org. When I was a kid, I somehow got a copy of NASA's annual spinoff review.

Well, Spinoff 2007 has just been published by the agency's Innovative Partnerships Program. Inside are 39 examples of how going out there is helping us down here, in fields ranging from health and medicine to agriculture and even recreation. We'll have to talk to someone about this new report sometime soon. Chris Russell of the Dawn Mission is coming up in just a minute or so. Here's Emily. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked,

Could either of the Voyagers have gone on to Pluto? I don't think anyone would wish to change the Voyager 2 mission, which accomplished flybys of all four giant planets. But there are some people who wish that Voyager 1 had followed a different plan. Voyager 1 visited Jupiter and Saturn, but during the Saturn flyby, it was commanded to fly very near Titan in order to closely examine this most enigmatic of moons, which was known to have a thick atmosphere that contained hydrocarbons and other building blocks of life. However, as Voyager 1 flew by, its cameras proved unable to pierce Titan smog, so the spacecraft returned nearly a thousand images of a place that was as featureless as a cue ball.

The close flyby tossed Voyager 1 out of the ecliptic plane, meaning that it was not able to continue on to any of the other outer planets. But mission controllers could have sent Voyager 1 to Pluto instead of doing the close Titan flyby. Should they have? Stay tuned to Planetary Radio to find out. Out there in deep space is a bird with 20-meter or 65-foot wings. Those wings are solar panels generating power for the bird's ion engines, delivering a gentle push that can last for years at a time. That's a good thing, as Dawn may have billions of miles to go before it sleeps.

After a quick swing past Mars in 2009, Dawn will head for Vesta, the third largest but second most massive asteroid in our solar system. The probe will circle Vesta for nine months before it does something no spacecraft has ever done before. Firing up its engines once again, it will depart for Ceres, the biggest asteroid in our neighborhood. It's an international effort, with participants including the Jet Propulsion Lab, Orbital Sciences Corporation, Los Alamos National Laboratory, two German agencies, and two Italian ones. Heading this team is Principal Investigator Chris Russell

of the University of California, Los Angeles, where he is on the faculties of both the Institute of Geophysics and Planetary Physics and the Department of Earth and Space Sciences. Chris's career began back in the days of the Apollo moon missions. He's virtually guaranteed work through July of 2015, the official end of the Dawn mission. But will that be the end? He recently talked with me from his office at UCLA. Chris, thanks so much for joining us on Planetary Radio.

And congratulations on seeing the Dawn spacecraft safely into its cruise phase as those ion engines drive it toward Vesta. Yes, this is the day we were looking for for a long time, and it's a real pleasure to see that spacecraft finally on its way to the destination it was built for. When you say a long time, you're not kidding. When did the genesis of this mission start? This started in 1992, and we had a workshop on the Discovery Program, and the Discovery Program was just beginning,

and we were teaming up with different people talking about their ideas and things, people talking about their ideas and things. And one of the people who came to this workshop was an engineer from the now Glenn Research Center, and then it was Lewis Research Center in Cleveland. And they had been developing ion propulsion systems at Glenn, but not having customers for them, basically. They knew that they would do great things but they didn't have anybody who had signed up to using them and I immediately saw what we could do in planetary exploration. So I directed this guy to look at the planetary applications and so he and I teamed up and we worked for a couple of years, and then we were ready to propose to NASA.

So you're running now with three of these ion engines that worked very well on sort of a test bed, Deep Space One. But now they're really pushing you out to do some great science. Yes, we have three thrusters. We use them only one at a time, so we're using them in exactly the same way as the Deep Space One mission used them. However, because we're going to do more thrusting than Deep Space One and because these thrusters have a finite lifetime, or we believe they have, well, we know they have a finite

lifetime. We've tested them on the ground. We probably haven't tested them to their limits yet. But anyways, we need to have three just to ensure that by the time we get to the end of the xenon fuel, the thrusters are still working fine. Would you remind us of some of the other ways in which this mission is really unprecedented, what it's going to achieve? Well, from a sort of mission scenario point of view, we go to two different bodies and orbit each and map each, and that has not been done before. We've sort of circled the Earth and circled the Moon and done things like that before, but we haven't gone out there into deep space and explore one body and then leave it and explore another.

That takes us more to the era of space exploration as it was envisioned in early science fiction, in practice even modern science fiction, where space travel is something you can do repeatedly, and it's not just a one-off trip. Seeking out new worlds. Yes. You and I both, I learned, are fans of the Dawn Journal by your colleague Mark Raymond, the project system engineer. And we'll put up a link to the Don journal, of course. Mark is the only one who's been on so far, although we've been following the mission pretty carefully. You have, what now, about 40 years before you reach that first target, asteroid Vesta? We will get to Vesta in 2011. Then we'll spend close to a year close to or in orbit around Vesta. And then we will leave, spend a little more than three years going over to Ceres, and

then spend at least half a year, but maybe a lot longer than that, in orbit around Ceres. At the present time, we're not planning to leave Ceres, but, you know, if we still have half a tank of xenon, who knows what we would do. You know, I was hoping you'd bring up something like that, or I was going to ask you. I mean, this mission essentially at this point ends at Ceres, but I wondered if you still have a functioning spacecraft

with lots of xenon, where might you go? At the present time, we have not explored. Earlier on, when we had a slightly different arrival time, we noticed that it might be possible to leave Ceres and then cut across the solar system to the point where the asteroid Pallas, which is almost the same size as Vesta, but at about the same average distance as Ceres, so it's a good comparison object with both, to where that asteroid was going to cross the ecliptic plane. Now, it has a high inclination, so we can't match orbits with it. It takes a lot of energy to get out of the ecliptic

plane, the plane that the Earth and most of the asteroids are orbiting in. But a flyby of Pallas would have been quite interesting for the comparison with Vesta and Ceres. But we do not know whether we could make that dash for that target right now. Talk a little bit about Vesta and Ceres and why they're such exciting destinations. Well, they're exciting destinations because they're fairly close but very different. You can think of Vesta, at least as we can see it today, not having got there yet, as an object that is very much like our moon. It's got lava flows across the surface, it's cratered, and it's got a density that's similar to the moon's density. So we believe that this body got very hot after the material came together. It melted and the iron

sunk to the center and the silicate, the lighter material, floated to the top, and we have basically a two-layer body, at least two layers, in which we have heavy material, a core sort of like the Earth, but probably very solid right now, and an outer mantle of silicate material, which is, again, a little bit like the Earth and certainly like our moon. So that's Vesta. That's Chris Russell, principal investigator for the Dawn mission. He'll rejoin us in a minute. This is Planetary Radio. Hey, hey, Bill Nye the Science Guy here. I hope you're enjoying Planetary Radio.

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Welcome back to Planetary Radio. I'm Matt Kaplan. The Dawn mission is making its way toward the asteroid Vesta. Principal Investigator Chris Russell of UCLA is just as excited about the spacecraft's following target, our solar system's largest asteroid, Ceres. Ceres is a much bigger object, but at the same time, it's less dense. It's not as dense. It's about half as dense, in fact, as Vesta is. And the only sensible explanation for that is that there's a lot of water together with the rock, so that the water is about one quarter of the density of the rock, and you mix, say, equal parts of the two,

then you're going to get a body around halfway in between. And that's what Sirius is like. Now, the next question you would ask is, well, is the water all mixed with the rock? Is it sort of a muddy planet? Or have they separated into into basically a rocky core and an ice water mantle. And we took some Hubble pictures and got it's size and shape very accurately. The body is very round, it's sort of in rotational equilibrium. The surface is an equi-potential, gravitational equi-potential, where everything is relaxed in an equilibrium with its rotation, except there's a little offset from that, which is consistent with the material

having condensed in the center. And, you know, with the density and the size and this shape, with a body that has about 400 kilometers in radius of rock and about 90 kilometers of water. You know, it looks like we have a global ocean of either ice or water on top of a rocky interior. So is there the possibility that we're going to get our first Is there the possibility that we're going to get our first long-term look at a body that's not so different from some of the outer moons that have intrigued us, the outer moons of Jupiter and Saturn? Precisely. An important difference between, let's say, the moons of Jupiter and Ceres is that it's in a much more benign environment. It's closer to the sun, and it's also not surrounded by an intense radiation belt. And when we started to understand that Ceres was wetter than we might have expected, then the planetary protection people said, well, when you get out there, please be careful. Back off. Do not get

too close. Arthur C. Clarke once said something like that. Yeah, but that was for Europa. Yes. Is there, and I'm sure listeners are thinking the same thing I am, and maybe you are, is there the possibility of liquid water under a layer of ice? Yes, there is. One of our team members, Tom McCord, has run thermal evolution models, starting with a reasonable mixture of starting materials, and the body differentiates into rock and water. Many of the runs that he makes, at the end, there's still liquid water. Many of the runs that he makes at the end, they're still liquid water. It depends a little bit about what is dissolved in the water and some of the starting conditions, but there is a possibility. We are looking at water that's underneath a hard ice shell with some dust

on top of that hard ice shell. So the ice is sort of insulated with dust. When we take radar measurements of the surface, it looks like clay, which is in clay is just dirt that has interacted with water. So we have a little bit of indirect evidence just from the radar measurements that there's a lot of perhaps water underneath the dust layer. And then underneath that very hard ice shell, ice is either soft and convecting or water in these thermal models. You're going to be sending back some, I'm sure, beautiful images of these two bodies, but I know that you're also going to be able to tell with a spectrometer and other things a little bit about their composition.

Yes. What we're interested in is besides just taking pictures, and our camera does take color pictures so that we get a little bit of information on the mineralogy from the camera. the camera. But in order to really pin down what the minerals are, we have a mapping spectrometer that maps both in the visible and in the infrared. And there are some telltale absorption features in the infrared that will enable us to distinguish one sort of material from the other. So we're looking here at minerals. But we're also interested in the elements that make up those minerals, you know, how much iron, how much magnesium, titanium, thorium, and stuff like that, and also hydrogen. To do that, we have a gamma ray and neutron detector called GRAND. That will tell us exactly how much of these various elements there are. So that will give us another big constraint on the evolution of these bodies.

You have your hand in so many missions, I don't think we have time left to talk about all of them. I mean, you told me a couple of weeks ago we needed to hold off, because I think you had a hand in 50 papers presented at the American Geophysical Union Conference a couple of weeks ago. Yes, and it was one of those things that sometimes that there are dry periods in your career, and that's because you can't, even though you can plan intelligently, there's a lot of things that go wrong with missions, and sometimes what happens is there's a sort of a traffic jam, and the missions all get launched at the same time, and so that all your results start coming down at the same time, so so that all your results start coming down at the

same time. So you can go through some busy periods in your career, and this is one of them for me. It never rains, but it pours. With just a few seconds left, one of those missions that you're involved with, well, one instrument, is the magnetometer on Venus Express. And we got this exciting announcement from that European spacecraft just recently. Yes, we finally got the electromagnetic signals that indicate that lightning is taking place on the planet, and pretty much planet-wide, and pretty much all the time. So similar to the Earth in that respect, that we have lots of lightning on this particular planet, and at Venus we have lots of lightning on this particular planet, and at Venus we have lots of lightning, too.

Chris, thank you for helping to bring back so much of the excitement of our solar system. Well, you're welcome to give me a call in four years. I look forward to it. In fact, if you don't mind, I'd like to do it well before that, certainly by the time of your Mars flyby. Okay, that would be very appropriate. Thanks very much for joining us on Planetary Radio. Okay, you're welcome.

Professor C.T. Russell, Chris Russell, is a member of the faculties of both the Institute of Geophysics and Planetary Physics and the Department of Earth and Space Sciences at UCLA, University of California, Los Angeles. Of course, he is also the principal investigator on the Dawn mission, which is now on its way toward Vesta and then on toward the largest asteroid in our solar system, Ceres. We will be propelled right along toward our weekly visit with Bruce Betts, this week's edition of What's Up, but that'll be after a return visit from Emily. I'm Emily Lakdawalla back with Q&A. Did the Voyager mission make a mistake when it chose to send Voyager 1 close by Titan instead of using Saturn for a gravity assist to Pluto? I think most scientists would say that the Titan flyby

was worth it. The image data was a little disappointing, but Voyager 1's trip past Titan accomplished several important firsts. For one thing, the spacecraft performed an occultation measurement, sending a radio signal back to Earth as it crossed behind Titan. As the radio signal weakened and then blinked out, scientists got a profile of the density and other properties of Titan's atmosphere and also got the first direct measurement of the diameter of the solid part of the moon. Before Voyager 1, no one knew how big Titan actually was. The encounter tossed Voyager 1 out of the ecliptic plane so that it was able to perform a similar experiment on Saturn's rings, using radio waves to map where the rings were densely populated with particles.

These data allowed the Cassini mission to plot a safe course through the rings when it arrived at Saturn two decades later. And finally, now that both Voyagers are on their way out of the solar system, the very different paths taken by the two spacecraft have shown that our solar system, defined by the region in which the solar wind holds sway, is squashed. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Well, we've got Bruce Betts not on the phone, but once again on Skype.

He's a little bit under the weather, but enough above the weather to give us a look at the night sky with this week's edition of What's Up. And how are you doing, Guy? You're feeling a little bit better, right? I am. I'm feeling a little bit better. Yeah, I'm really... I'm excited and energized, as always.

Yeah, I'm glad. And I was just sorry that we couldn't record at the annual holiday party at the Planetary Society and have all kinds of people staring at us and laughing their hearts out. Yes, me too. Hey, have you been checking out Mars? I have. Good, because it's the brightest it's going to be for many, many years right now. Coming up around sunset in the east, setting around dawn in the west,

at opposition on December 24th, but remaining bright for a while afterwards. It's about as bright as the brightest star in the sky, which is Sirius. And in fact, I really enjoy, I mentioned it before, but if you're out late in the evening, look off to the lower right of Mars, the orangish-reddish bright thing, and you'll see Sirius, very similar in brightness, the very bright star, but very bluish in color. So a nice comparison between the lovely colors of the night sky. We also have Saturn rising in the middle of the night. In the pre-dawn sky, you can check out Saturn high overhead.

And you can check out Venus, as always, extremely bright over there in the east and the brightest star-like object up there. You can still check out comet homes with binoculars if you go looking in Perseus as a nice fuzzy ball. This week in space history, of course, had Apollo 8 returning to Earth after their lovely reading of Genesis as they went around the moon for the first,

humans doing it for the first time. And we should go on to random space i was so worried that you wouldn't be up to it i'm sorry i'll try to make up for it it was a valiant effort it was thank you i'm going to talk in the trivia about gaps and exploration of planets and and a lot of people think there was there was a big gap with Mars, but people think of Viking in the late 70s, Pathfinder 97. But of course, there was the Phobos 88 mission from the Soviets had two spacecraft, one of which failed en route to Mars, one of which failed after two months in orbit around Mars. And of course, the real random space fact is I did my Ph.D. thesis on Phobos 88 data.

Huh. Huh. That is random. Isn't that random? Wow. And it's space, and it's a fact. And it got you a Ph.D. It did.

I have one of those somewhere. Let us go on to the trivia contest. We asked you, Who is the only woman from the first NASA astronaut class to include women who is still an active astronaut? How'd we do, Matt? I hear there's a little controversy out there. There was a bit. I was almost evenly divided.

I think there might have been a slight majority for Anna Lee Tingle Fisher, who, as you pointed out, actually left the astronaut corps and then came back. Yes, went off, raised family, came back into the corps and is technically active right at the moment and is who I was looking for. Other people, I guess, said Shannon Lucid. And we're flexible, so we can give you that. But she isn't, to my knowledge, in the active astronaut pool right at the moment. So either answer, and how do we do in randomly selecting a winner this week? As it turned out, Random.org selected Stephen Hansen of Beaver Creek, Ohio, and he said Anna Lee Tingle Fisher. So, Stephen, a Planetary Radio t-shirt will be on its way to you shortly.

All right. I suggest that for our next contest, we give away a page-a-day calendar, astronomy page-a-day calendar that the Planetary Society is partnering with and the official calendar of this week in space history and other good facts and wonderful things. So we'll give that away for the winner of the contest that I announced today. And that is, what planet has it been the longest since it was last explored by a spacecraft, giving us the longest gap since it's been explored by a spacecraft? By a spacecraft, I mean up close and personal, some type of flyby or better. Go to planetary.org slash radio. Find out how to get us your entry.

And you've got until December 31st, last day of 2007, at 2 p.m. Pacific time, Monday the 31st at 2 p.m. Pacific. That's it. I sure hope you're feeling better. We want to spend more time with you and do it in person for next week's show. Thank you. I hope so as well. And everyone else, I hope you're healthy out there and happy holidays.

Go out there, look up at the night sky and think about mistletoe and where you'd like to place it. Thank you and good night. I can imagine several very good places. None of them have anything to do with Bruce, by the way. He is Bruce Batts, the director of projects for the Planetary Society. And he joins us every week here for What's Up? And watch out for those little leaves hanging over your head. I just meant as a decoration.

Thanks so much for helping to make 2007 a wonderful year for Planetary Radio. We have big plans for the next 12 months, including our welcome for weekly commentator Bill Nye the Science Guy in just two weeks. Our program is produced by the Planetary Society in Pasadena, California. Have a great week and a wonderful new year. Thank you.