Planetary Radio: Space Exploration, Astronomy and Science - Sami Asmar: The Man Who Told Us The Huygens Probe Made It

Episode Date: February 7, 2005

Sami Asmar: The Man Who Told Us The Huygens Probe Made ItLearn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

The man who told the world Huygens made it, this week on Planetary Radio. Hi everyone, welcome back to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. JPL scientist Sammy Asmar is our guest. He seems to be making a habit of being the first to know about a spacecraft's success. We'll talk to him about his most recent experience and how one of Huygens' most critical experiments

was saved from failure. You enjoy Bruce Betts on our What's Up segment each week. Are you ready to see him on TV? Is he? Well, we'll find out when he offers up another trivia contest later today. Here is a sampling of news from around the solar system. Scientists are wondering why Saturn's south pole is the warmest spot on the planet. These findings came not from the Cassini orbiter this time, but from Earth-based telescopes.

On the other hand, Cassini has noticed an odd dark spot in the haze surrounding the ringed planet, a spot centered right over the South Pole. You can check out the images at planetary.org, which is where you can also read about glowing Mars. It's called Night Glow, and it has been discovered by the European Space Agency's Mars Express orbiter. The very faint ultraviolet light appears to be caused by chemical reactions in the Martian atmosphere. And back here on Third Rock, the glow is coming from political heat in Washington. By the time you hear this show, NASA will have begun sharing news about its 2006 budget. We'll bring you more on this subject next week.

It's safe to assume a rolling stone on Titan gathers no moss, but what would make it roll in the first place? Emily knows. I'll be right back with Sammy Asmar. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, Titan's rocks are made of ice and its rivers are made of methane. Would a methane river on Titan be able to carry large ice boulders long distances?

When the Huygens probe descended through Titan's clouds, she found a surface on Titan that looks surprisingly familiar to the Arizona-based imaging team, a landscape of dry riverbeds, gullies, deltas, and flat basins. But the materials that Titan is made of are completely different from Arizona's. Titan's rivers would flow with liquid methane leavened with other hydrocarbons, and they would flow over rocks made of frozen hard water ice with a little ammonia mixed in. These materials do not have the same properties as the liquid water and silicate rocks that the earth is made of. As a liquid, methane is runnier than water, having a lower viscosity. Also, the methane on Titan would be much closer to its boiling

point than water is on the earth. As for the rocks on Titan, water ice rock is far less dense than silicate rock, making Titan rocks pretty lightweight. That's reinforced by Titan's low gravity, seven times lower than the Earth's. How do all these factors combine to affect Titanian geology? Stay tuned to Planetary Radio to find out. Sammy Asmar is manager of the radio science group at the Jet Propulsion Laboratory. He spends a lot of time working with the Deep Space Network, or DSN,

that chain of radio telescopes that keeps track of spacecraft like Cassini. But in early January, he was at the Green Bank Radio Telescope in West Virginia, listening for a faint report from the Huygens probe, signaling that it was descending slowly through the thick atmosphere of a very cold world. We recently talked about the experience at Planetary Society headquarters, beginning with a discussion of the weather. So, Sammy, I understand that the signal coming back from the Huygens probe on this frigidly cold little moon Titan was almost not to be received because of snow, snow in West Virginia. In fact, the forecast that week in West Virginia, in the hills of West Virginia,

where the Green Bank telescope is located, was for snow. And we were very concerned. My colleague at JPL, Bob Preston, kept checking the weather forecast and calling me and saying, is there any snow? And, in fact, to our luck, the snowstorm was delayed about 24 hours, and it started snowing as we were done and leaving. If it had really snowed a few hours earlier, it would have affected the quality of our signal. It would have increased the so-called system noise temperature, reducing the signal-to-noise ratio, etc.,

but in other words, degrading the quality of the signal. And if that snowed enough, it could have prevented the experiment from taking place altogether as the telescope itself would have its own limits in handling the snow and the winds. In fact, it was very windy, and it had the day before exceeded the threshold of the wind for the structural integrity of the telescope itself. Again, we were lucky.

Then night or the morning of the observation, things turn around. Almost nothing but good fortune involved with this little Huygens probe. You were, because everything worked, you were the first person to actually know that Huygens was successful. I guess when that signal started to come in, it came in so perfectly, so on mark, that you thought maybe something was wrong? In fact, I have to admit I was suspicious because of a few things. One is that the timing of the signal was practically perfect. It appeared when we expected it to.

Typically with these things, there's a delay or there's uncertainty in how much you predicted the timing of the events. After all, we're talking about an event a billion miles away. Absolutely. The other thing is that the strength of the signal, we had done some calculations that showed it to be a relatively weak signal. After all, it was not designed to be an experiment between the probe and Earth. It was designed to be between the probe and the Cassini orbiter. So our link budget, as it's called, for the reception on the ground predicted a weak signal.

I was not even sure we would see it on the display in real time. But as it happened, a relatively strong signal and relatively, you know, in the context of our expectations, showed up on time at the right frequency and at the right time. At that point, I was really tempted to scream back on the telecom phone line to my colleagues, Bob Preston again and Bill Faulkner, the principal investigator, as well as the Europeans at the European Space Agency Operations Center and Darmstadt, who had been also on the phone and waiting to hear the news. But I had to kind of hold myself.

My other JPL colleague, Sue Finley, who was traveling with me and was sitting next to me, I could see the anxiety on her face and the look in her eyes saying, say something. The reason I wanted to wait was to prevent a false detection, so to speak. Yeah, you wouldn't want a false positive. False positive and raise people's expectations. detection, so to speak. Yeah, you wouldn't want a false positive. False positive and raise people's expectations. So I waited a few seconds to a few tens of seconds for my display to refresh itself, meaning just give it a little bit more time to get a small pattern. And indeed, it was there consistently. And that's when I just felt the relief and my tension dropped

and I got on the phone and I announced that we indeed can listen to the Hogan's Probe from Titan all the way out there. I bet those few seconds that you held off felt like a lot longer. Suddenly everything was quiet. The phone lines were quiet, the people around me, the staff. You had about 12 people in apparently a pretty small control room, hardly a conference room, not normally holding that many people. That's correct.

So they were all by that time huddled around us and seeing what we see. But, again, they were leaving it up to me as the trained person in this particular instrument that we brought with us from JPL on loan from the Deep Space Network. And it's called the Radio Science Receiver. This rack full of equipment that you actually had to have shipped to this big dish in Green Bay. Correct. Excuse me, Green Bank.

We had borrowed it from the Goldstone Deep Space Communication Complex, in other words, the DSN site in California. And it was shipped a few weeks in advance prior to our arrival. So the point is everybody was looking at me like, is this what we think it is? And, you know, we're waiting for you to kind of tell us that it sure is. And you mentioned you were on the phone. You had in this conference call JPL and all the people at the ESA facility in Darmstadt, where our Emily Lakdawalla was also waiting with bated breath,

all of them on the phone waiting for you to say, yeah, hey, it's there. And when we did, they were celebrating. The control area at JPL was fully staffed, as far as I was told. The director was there and was talking to my colleague. And we faxed plots and so on, and there was a lot of interest in seeing the actual data. And by that, I mean just this carrier of the radio signal. And the Europeans got on the phone up to Dr. Leberton, the project scientist. Jean-Pierre Leberton.

Jean-Pierre Leberton. And he was very emotional, he was very warm, thanked me personally, and was very pleased, you could tell. But also on the same teleconference line were the other stations that were involved with this activity, where my other JPL colleagues were present. We need to take a break in just a couple of moments, but I want to leave people with something that you told me just before we turn on the recorder, that this is not the first time that you've been the first person to hear that a little probe had actually reached its goal. It is an amazing privilege, and I'm not sure how this happened. But I did similar work on the Mars Pathfinder, the little rover, and it landed on Mars on 4th of July, 1997.

And that was another complicated communication scenario where they required people like me, so-called radio scientists, to bring in these equipment, specialized instrumentation. And at that time, I traveled to Madrid, Spain, at our Deep Space Network site, again, to perform a similar function. And, you know, to perform a similar function. And, you know, there was another historical event. I'm very thrilled about that.

He is Sami Asmar. He is the manager of the radio science group at JPL. But he is also the co-investigator on the Doppler wind experiments on the Huygens probe. And when we come back, let's talk a little bit about that. And, in fact, how some of the work you did managed to save some data which might have otherwise been lost from Huygens so we will return 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.

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Planetary Radio is back with our guest this week. Sammy Asmar is the manager of the Radio Science Group at the Jet Propulsion Laboratory, very near Pasadena, California, where we are sitting at the headquarters of the Planetary Society, talking about his recent involvement, very exciting involvement, with the Huygens probe, which was so successful on Titan, that moon of Saturn, delivering back-to-Earth data that's probably going to keep a lot of scientists busy for years. And in fact, you're one of those scientists. You are, in addition to your everyday JPL duties, the co-investigator on the Doppler wind experiment. So tell us a little bit about that. Have you also gotten back good data from that experiment? And what is it going to tell us about Titan? The intent of the Doppler wind experiment is to measure basically the wind

speeds and direction in the atmosphere of Titan by monitoring the motion of the probe itself as it descends and eventually lands. As it moves due to the effect of the wind, and you have a radio signal being continuously transmitted from it to the Cassini orbiter, as well as Earth as it happened, there will be a shift called the Doppler shift in the radio signal that is proportional to the amount of forces acting on the probe. And I'm sure most of our audience knows that we're talking about the famous train whistle effect,

which affects electromagnetic waves like the signals coming from Huygens as well. Exactly. So the intent for the Doppler wind experiment, again, to measure the nature of winds, their speeds and direction, and the original design was for a radio link to exist between the probe, Hogan's probe, and the Cassini orbiter. Our work recording the signal on the ground was supposed to be additional work to enhance this experiment by receiving yet another, say, vector, another direction of this Doppler information on the ground. And it was a best effort spaces, see what we can do. It was practically just a cute little project at the time.

But a backup for what was supposed to happen. A backup and an enhancement. And as it happened, unfortunately, some of the instrumentation involved in the Doppler wind experiment, as originally designed, did not function properly. And as a result, we lost the data that was supposed to be recorded on the spacecraft. And when that happened, our recordings on the ground ended up being the only Doppler wind experiment. So in essence, we had salvaged the experiment. And we have since then, indeed, reconstructed the frequency, the Doppler profile,

and have in our hands a wind profile. So we already know the nature of the winds on Titan, their speeds and directions, and that will be ready for publications. And I'm sure you'll understand we probably should not be discussing stuff that should be published because journals would like to have the first news on that. We're always tempted to push, but no, we'll let it wait until it's out there in print. But the point is that we have succeeded in retrieving the original intent of the experiment. So not just you, but a lot of other researchers were, I'm sure, are thrilled that this data, which would have been lost altogether, was salvaged because of this little enhancement that you guys had in mind.

Absolutely. And we really should thank the management of the Jet Propulsion Laboratory that supported this work and gave us the tools and the resources to carry out what we wanted. The principal investigator of the Huygens-Doctor Wind experiment is Dr. Mike Bird in Bonn, Germany. He had initially thought he had lost his experiment, but was very pleased to hear that we had recorded it, and we have since been working with him on processing the data.

And I know that my colleague Emily Lakdawalla has been talking to Mike, as she has to you, and by the time this radio show is on the planetary.org website, there should be a nice detailed article by Emily based on all of her conversations with all of you. There was another experiment, the VLBI, very long baseline interferometry, which I guess you also had a relationship with? Our work on the Doppler wind experiment ground recording was actually done under the umbrella of a larger experiment called the VLBI, very long baseline interferometry, which was coordinated by a European institute called the Joint Institute for VLBI in Europe, or JIVE. And Dr. Elena Gervitz was the coordinator. This group had coordinated with several, up to 17 radio observatories around the globe

to participate in the VLBI experiment. And out of those, we have selected six, a subset of those stations, to take equipment to receive our subset of the experiment, the Doppler wind experiment. receive our subset of the experiment, the Doppler wind experiment. The VLBI experiment, the intent of that is to narrow down the angular information in terms of direction and landing site of the probe. And to do that, they would track or receive signal from the probe for, say, a couple of minutes. Then they would point the ground antennas to a quasar or a natural radio source for,

say, another couple minutes and back to the probe and so on and so forth. And the idea is to use the quasar as a reference signal that will help you narrow down the angular information. Since it's rock solid and it's a long, long, long ways away. Go ahead. But I think I read that you were a little concerned because this, as a radio scientist, this whole idea of finding this still fairly weak signal coming from a billion miles away, then looking away at a quasar and then trying to come back and find it was a little bit, made you a little anxious.

Indeed. Since I'm trained as a radio scientist who tries to extract a weak signal out of a lot of noise from a spacecraft, once you point to the spacecraft and find your signal, you don't point away. And the VLBI colleagues wanted to do this every few minutes. So it went against my nature, but of course, it worked well. We are just about out of time. And I want to go back to the Doppler experiment for a moment, because I forgot to ask this question. It seems incredible to me, a billion miles away, that you would be able to use something as subtle as the Doppler effect to detect minor changes in wind speed. I mean, what kind of, unless this is something which needs to wait until that published article comes out,

what kind of resolution, what kind of differences in the speed of the wind were you able to detect using this method? Well, let me first tell you the key to this. We had a stable signal reference, what we call an ultra-stable oscillator. In fact, it was a rubidium atomic clock miniaturized that was flown on the Hogan's probe. No kidding. And that is the key to this. It is the ultra-stable oscillator on board the spacecraft that maintained a relatively stable radio signal. And there was obviously also stable references on the ground stations had the original experiment worked, a stable reference on the Cassini over as well.

So that was the key to us achieving our science objective. There was a second link from the probe to the orbiter that worked well that was not referenced to this stable reference. And, in fact, it was too noisy for us to reconstruct the Doppler wind experiment. So, again, the key to achieving, and this is a good plug, that I always like to tell people, fly ultra-stable oscillators on your spacecraft. Go with atomic clocks. Exactly. We're out of time, Sammy. I'm going to put you on the spot for just one other thing. I have learned that there may be some sound that we could play for people having to do with the Doppler wind

experiment. Some of it is, I guess, on that Jive site, but I hope that we can maybe pick up some of that from you and provide it for our listeners to enjoy. We've done this in the past. One can take the radio signal and convert it to an audio signal, and hopefully it will be interesting to people where you can hear the equivalent of motion, maybe even the landing, things of that nature that we'll try to make available to you.

Well, we will encourage people to visit our Sounds of Titan and Mars area of the website, planetary.org. And again, there will be an article, probably is an article in place as you are listening to this interview, this conversation with Sammy Asmar, which you'll be able to find at planetary.org. Sammy, thanks very much. I know you've got to get back over to JPL, but I really appreciate that you could take a few minutes to join us here on Planetary Radio. Thank you very much. Sammy Asmar is the manager of the Radio Science Group and the very happy co-investigator on the

Doppler Wind Experiment for the Huygens probe, now still sitting and probably will be sitting for a very, very long time on Titan, the great moon of Saturn. We'll be back with Bruce Betts and what's up right after this return visit from Emily. I'm Emily Lakdawalla, back with Q&A. Methane rivers on Titan are runnier than Earth rivers, which might make it harder for them to wear down Titan's rocks to make dramatic landscapes. But this effect is counterbalanced by two factors. First of all, methane rivers on Titan would be near the boiling point.

As they eddy and swirl in turbulent flow, local drops in pressure in the rivers can actually cause pockets of boiling. This process, called cavitation, pits and erodes propellers in boats on Earth's oceans and could have a similar erosive effect on Titanian rocks. Another factor that would help erosion on Titan is that Titan's rocks, made of relatively lightweight water ice, would be much more buoyant in methane rivers than Earth's silicate rocks are in water rivers. That, plus Titan's lower gravity, would make it much easier for Titanian rivers to move large boulders long distances, making it perfectly possible for Titan to have dramatic, sculpted landscapes like those of Arizona.

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 with the Director of Projects for the Planetary Society, Dr. Bruce Betts. And we are once again on location.

We are indeed. Here we find ourselves at Cal State Dominguez Hills. We are in the television studio right now even as we speak. And we're going to tell people why toward the end of this What's Up segment because it's pretty exciting, something that's going to happen soon and people will be able to tune into a new starring role for Dr. Betts. But tell us what's up first. Well, got those friendly planets, but fewer and fewer. But Saturn's looking great in the evening sky.

It's near Castron Pollock, still bright, yellowish, rising, just around sunset, up in the early evening, looking beautiful. Got in the pre-dawn sky, you can catch Jupiter looking extremely bright in the east. And you can also catch Saturn if it's an hour or two before dawn in the west. We've pretty much lost Mercury and Venus. No one knows where they are. Mars is still out there in the pre-dawn sky. You can see it, but it's kind of dim and reddish and below Jupiter.

It is still a great time to look at Saturn. We've had this very clear-skied evenings here in Southern California, our famous Santa Ana conditions. And I'm going to take the telescope out again tonight, I think, and get one more look before we cloud over again as we head into spring. Cool. Look for Titan if it's out there. It appears a little tiny white dot off to the side. I will do that and I'll think of

today's guest. Indeed. Alright, we move on to Random Space Fact! On Mars you can actually see solar eclipses, though partial ones, up to three times a day with

Phobos and throw in an occasional Deimos during some times of the year. It's interesting because from where Phobos is and Deimos, you get eclipses daily part of the year and then you get nothing for the rest of the year. Phobos has only an eight-hour orbital period, so it's actually in the Mars days, similar to an Earth day. So the implication is about three times a day it's there. Obviously, you'd need the ones in the daylight to actually be able to see it crossing the sun's disk. But it works out that it does not block the entire sun, just about 30% of it. They're little guys.

They're little guys. Now, Phobos is really close compared to our moon. And so that's why it even blocks out 30% of the sun. Deimos, not so much. Mars Exploration Rovers actually got pictures of the eclipses. They're really very, very cool. You'll be able to see those in my upcoming, well, you know, that thing we'll talk about. Oh yeah, the one that we're going to talk about in a minute. Yeah, I mean, I actually show those. I got to ask you one other

question, which is probably stupid. Are Phobos and Deimos, are they orbiting Mars in the same plane? Yes. So in the equatorial plane of Mars, which is kind of how things usually work out for the small satellites. They end up close. The tidal forces and other forces end up not only putting them in synchronous locked rotation, so they're always pointing the same side towards Mars, but also put it in the equatorial plane. Well, thank you for clearing that up. Sure. My pleasure. Trivia contest.

All right. I should fess up first. As I said at the end of last week's show, I messed up, folks. So we are off by a little bit this week with the trivia contest that we were about to provide the answer to. The question was? The question was, what is the gravity at the surface of Titan as a percentage of the gravity at the Earth's surface, often referred to as 1G?

What's the gravity on Titan's surface? How did we do, Matt? We did well. They did well. They, being our wonderful listeners, we got all kinds of great answers. Not a lot of funny ones this week, but it's kind of hard to turn this into a funny joke, a funny ha-ha trivia question, I guess. So we'll just go ahead and tell you who won.

And it is Ivan Ulrich, our Ulrich of Campana, Argentina, who had the correct answer, rounded at least to the nearest whole number, 14% of Earth's gravity. We had a lot of 13.7s and 13.8s. Ivan, thanks so much. You're going to be getting in the mail that Planetary Radio t-shirt. Nice job. And if you want to win your own Planetary Radio t-shirt, answer the following question. What is the largest moon of Uranus?

What is Uranus' largest moon? Go to planetary.org slash radio to enter our contest. Okay, now, quickly, why are we at Cal State Dominguez, a university in Southern California? We are here because starting this coming Monday the 7th, I am going to be teaching an introductory astronomy planetary science class that will be available via the web, via Southern California cable stations and TV. But anywhere in the world, you can log in and actually log in live, although that would be kind of uncomfortable if it's the middle of the night, or you can watch the shows

archived. If you do it live, you can actually call in on an 800 number, ask questions, send email to ask questions. It'll be a party. We're going to be taking a tour through the solar system over the next 13 weeks. People can find out more. Probably the easiest is go to

our website, planetary.org slash bets class, B-E-T-T-S class. Not that I have class, but I will have a class. So go there. You'll learn about this nice, interesting opportunity through our partnership, Planetary Society, with California State University, Dominguez Hills. You're not going to let this go to your head, are you?

I already have. Oh, yeah, okay, I'm sorry. Say goodnight, Bruce. Goodnight, Bruce. All right, everybody, go out there, look up in the night sky, and think about the hidden talents that your neighbors might have. Thank you. Goodnight.

They're not so hidden in my neighborhood. That's Bruce Betts, the Director of Projects for the Planetary Society. You can hear him each week right here on What's Up. And, gosh, now see him each week as he teaches astronomy from Cal State Dominguez Hills in California. Frightening, isn't it? By the way, the deadline to get us those trivia contest entries is Monday, February 14 at noon Pacific time. We'll be back next week. Take care, everyone.