Planetary Radio: Space Exploration, Astronomy and Science - Cassini-Huygens Reaches Saturn

Episode Date: July 5, 2004

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Cassini reaches the Lord of the Rings this week on Planetary Radio. After a seven-year journey, the Cassini-Huygens spacecraft has successfully gone into orbit around the Ring planet. Stay with us for a special report. Bruce Betts also gets in on the Saturnalia in this week's What's Up? And Emily Lakdawalla is here with a little tribute to a titanic moon of Saturn. I'll be right back. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, How can Saturn's moon Titan, which is less than half the size of the Earth, have a thicker atmosphere? Titan's nitrogen-rich atmosphere is about one and a half times thicker than our own,

and it's true that smaller bodies, which have a lower escape velocity, aren't as good at holding on to their atmospheres as larger bodies are. But size is not the only thing that matters. The other major factor is temperature. Gases escape from planets when chance collisions give gas molecules enough speed to escape the planet's gravity. The colder an atmosphere is, the slower its molecules move, and the less likely they are to escape.

Titan, which lies ten times farther from the sun than the Earth does, is far colder than the Earth, and so it is able to hold on to its atmosphere. But if that's true, why aren't there other moons with thick atmospheres in the outer solar system? Stay tuned to Planetary Radio to find out. That eerie music is the planet Saturn welcoming a weary traveler. To be a bit less romantic, it is the highly compressed sound recorded by the Cassini-Huygens spacecraft as it passed through the edge of Saturn's magnetosphere, or magnetic field, right where the charged particles of the solar wind were smacking into it. Fortunately, the school bus-sized spacecraft got through this

and much more dangerous obstacles without a scratch. Seven years in space, whipping past other planets for a boost to a ringed beauty a billion miles away. And the journey climaxed just past 6.30 p.m. Pacific time on Wednesday, June 30. Some of the engineers and scientists gathered at the Jet Propulsion Lab near Pasadena, California, had been working on this project for two decades. They came together from 17 countries to create the most complex space voyager ever. Now, they waited for word that Cassini-Huygens would take the last vital steps to achieve SOI. Here's an explanation from lead propulsion engineer Todd Barber.

SOI stands for Saturn Orbit Insertion. We need to let Saturn's gravity capture us into orbit. We have to slow down the spacecraft, otherwise we fly by, never to see the ringed planet again. So we have to slam on the brakes tonight with a 96-minute burn, and this is the longest burn that will be performed on the spacecraft during the whole mission, and it has to go perfectly tonight. Dave Seale is a Cassini mission planner. He noted the past visits to Mars made by Pioneer and Voyager missions 25 or more years ago.

But in their brief flybys, these craft generated more questions than answers. There was definitely mystery solved by those spacecraft, but definitely a lot of mysteries that were created. They discovered new satellites, new rings. They were only in the neighborhood for a very short time. They buzzed through in the fast lane and will be there to stay for four years, 76 orbits, over 50 close flybys, and will definitely unlock most of those mysteries. It's interesting to note that in our very first passage by Saturn,

Cassini will be closer than any of those spacecraft at only 12,000 miles above the cloud tops. Now, that sounds like a long distance, but spacecraft at only 12,000 miles above the cloud tops. Now, that sounds like a long distance, but Saturn is over 75,000 miles wide, so it's really a very small fraction of the diameter. If we were a fighter plane, we'd definitely be buzzing the tower, you could say. All stations on that, SOI systems, just an advisory. We're coming up on the time that the critical sequence will initiate the turn to the SOI burn attitude. This turn will be commanded at 7.20 p.m. local time and has a nominal duration of 9 minutes and 43 seconds.

This gives us a turn complete time of about 7.30 p.m. local time, although SOI comm should be able to see a signal before turn complete. The burn command will be sent at 7.35 p.m. local time, and the actual burn will begin seven seconds later. SFP, SOI systems, what is your subsystems data and are you ready to support us by? SFP is nominal and is ready to support. Copy. Contingencies? Contingencies is nominal and ready to support.

Copy. Power? You could definitely feel the tension as the time for the burn approached. The mission controllers had to trust that their careful programming would do the job. With radio commands taking an hour and a half to reach across space to the probe, Cassini was now entirely on its own. While all of us at JPL waited, we listened to commentary from folks like Bob Mitchell, the Cassini-Huygens project manager. He talked about the significance of the babel-like assortment of languages

you could hear all over JPL's auditorium, from scientists, engineers, guests, and reporters. This mission probably has the most international cooperation of any interplanetary mission that we've ever flown. Our partners are the European Space Agency and the Italian Space Agency, but in addition to that, a number of other European countries also participate. It makes it a very interesting mission to work on in dealing with all the different countries, the different partners that are involved with us.

The talent, the capabilities that we get from all these other countries, they bring skills, capabilities that we'd be awfully hard-pressed to do by ourselves. The complexity of this mission just wouldn't be here without this scope of international partners. With his work as a rocket scientist done for the night, Todd Barber was serving as play-by-play announcer. He felt the need to explain when the TV cameras in the Mission Control Center showed us a jar of nuts being

passed from hand to anxious hand just before Cassini would pass right through a gap between two of Saturn's rings. The consuming of the lucky JPL peanuts. The first six Ranger spacecraft failed in the early 1960s. Someone brought in some peanuts for morale building for Lucky Ranger 7. It worked just great. It's been part of the JPL folklore ever since. We're generally not superstitious as scientists and engineers, but yet the lucky peanuts almost always make it into critical mission events at the Jet Propulsion Lab. Doug Johnson just reported a signal. We've survived the ring plane crossing through the F and G rings.

One hurdle down, one to go with the start of the burn a mere nine minutes away. We all waited for the sole indication that Cassini's rocket engine had fired. Failure would send the spacecraft speeding right past Saturn toward the distant cold stars. We're approaching two minutes before the SOI

burn. Hopes and dreams of thousands of scientists and engineers are resting on the next few moments. So Godspeed Cassini-Huygens. May we see you in orbit. We have a Doppler signature with an engine turn on. Yes! Lots of high fives and celebrations and mission control. High fives and celebrations and mission control. So, the rocket engine was working, but would it burn for the full 96 minutes required to put Cassini into the planned orbit?

Once again, the only way to know it had worked properly was for the radio communications crew to listen carefully for a change in the vanishingly weak signal coming from the probe. The famous Doppler effect would do the trick. As Cassini slows, the frequency of its radio signal changes at a barely perceptible level. When the rocket engine shuts down, this change in frequency should flatten out or stop. The seconds ticked away, and then... Go ahead, S.O.S. The Doppler has landed.

Woo! All right. Okay, we have burn complete here for the SOI orbital incursion burn. The revelry continues here in Mission Control. Everyone's standing. Here comes the big boss. I think I'll shake his hand. You did great.

Thank you. You did great. My pleasure. Todd remembered a bit of cargo being carried by Cassini-Huygens. This is a good time to welcome into Cassini orbit 660,000 virtual visitors to Saturn. Cassini orbit, 660,000 virtual visitors to Saturn. Years ago, many of you are probably watching tonight, you submitted your signature. It was scanned on a CD-ROM, placed on board the Cassini spacecraft.

So tonight your signature sits in Saturnian orbit. Welcome to the sixth planet from the sun. Todd can be forgiven if he mistook a DVD for a CD-ROM, but it did indeed carry the digital images of well over 600,000 signatures from Earth, all scanned by the staff and volunteers of the Planetary Society. I'll be back with more of this special report on Cassini at Saturn, right after this message. 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. You can learn about these adventures and exciting new discoveries from space exploration in The Planetary Report. The Planetary Report is the Society's full-color magazine. It's just one of many member benefits. You can learn more by calling 1-877-PLANETS. That's toll-free, 1-877-752-6387. And you can catch up on space exploration news and developments

at our exciting and informative website, PlanetarySociety.org. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio, where we are continuing our special report on the Cassini-Huygens mission in orbit at Saturn. Now safely in orbit, it was time for science to take the front seat. Of course, Cassini had been collecting images and other data for years, and had even collected ring images as it reached orbit. In the early morning of Thursday, July 1, the first of those images began to arrive on Earth,

where the head of the imaging team, Carolyn Porco, eagerly awaited them. This is a first. This is really a first. And still we're seeing very sharp edges. That's a very scientifically intriguing result. Sharp edges in a ring system like Saturn's, where the particles are colliding, should not be there unless there is some physical process halting them from spreading. And there have been predictions and verifications in Voyager data that sharp edges should exist on the scale of one kilometer. That means a ring would go from dense to empty on the scale of about a kilometer.

But here we're looking at something that's a fifth that size. Oh wow. Okay, look at that. Now it's really getting exciting and I'm proud to say I took these pictures. Nicely done. I planned these excursions. Oh, that's beautiful. Maybe it's the kind of

picture only a ring scientist can love but I think it's beautiful. Oh, oh. this is gorgeous. This is really gorgeous. So that is almost certainly one of the bands in the Cassini division. Oh, and look at that sharp edge. Boy, that brings tears to my eyes. That's gorgeous.

Later in the morning, with 61 beautiful, revealing photos downloaded, Carolyn Porco joined other notables on the stage at JPL for a press briefing. I can't tell you how happy I am to be here. I don't think you have to be a ring scientist to imagine what last night was for us. It was beyond description, really. It was mind-blowing. It was every adjective you could think of. Even though we've had a long time to think about our images, we've planned them.

We chose the exposures, the filters. We know what we were looking at. I'm surprised at how surprised I am at the beauty and the clarity of these images. They are shocking to me. They were so shocking, I thought that my team here was playing tricks on me and showing me a simulation of the rings and not the rings itself. Literally, the image that when they shot, I'm still not convinced it's real. This is like textbook physics, textbook ring physics right there in one image.

I can't describe how exciting this is for us and how just mind-blowing the whole thing is. With Carol and Porco on stage was David Southwood, science director for ESA, the European Space Agency, builder of the Huygens probe that will leave Cassini and fall into the atmosphere of Saturn's moon Titan early next year. Southwood has devoted a good part of his life to this international mission, and he expects to spend many more years analyzing the data returned. It made me. It's part of me. It's made me the way I am. But equally well, I've got to say, it's going to be my retirement. I have to tell you, I don't expect all of the data from this mission

to be mined, to be finished, when I finish being Director of Science at ESA. And for me, my retirement is going to be looking at that data. It's not going to go away. And there is no way. You will get the immediate excitement as you see the new things. But science doesn't end just with the instantaneous hit you get from looking at a new image, looking at new data. It's piecing together the detective story that shows you the whole picture. And it takes years. And I say, I'm planning on my retirement.

Other people go fishing. Southwood expressed his satisfaction and pride when asked about the international participation in the Cassini-Huygens mission, especially through partnerships with the European Space Agency and the Italian space agency, ASI. But he also had some candid comments about his continent's future plans for space exploration, or the lack of them. He clearly prefers an active and important role for the European community

as a partner with the United States, and perhaps on its own. I mean, what Dr. Southwood thinks isn't half as important as what people in Europe want to do in the exploration of our solar system, what their plan is for the future. I think one of the great things of this year for me was the fact that the President of the United States actually declared we're going to do something. declared we're going to do something. It's a strategic view, so there's an enormous amount of work to put in place what is required to do it. But at least you had an idea of what would be the main axes of the approach.

I have to say, in Europe there are many ideas around, but we have not formulated how we're going to do the same thing, what we want to do. And I think that really is Europe has to grow up a little bit and recognize it should think how it would want to do the exploration of the solar system. When we came up with a plan a year or so ago called Aurora, it actually missed out the moon altogether. It said we would go to Mars direct. Do we really believe that? I mean now we think again because our American colleagues are approaching it a different way. I think we in Europe have to really get our act together

because it's fine science you can go off and fight on many fronts at once. You can do lots of different science. You can look at the beginning of the universe to what's going on between the Earth and the sun today. I mean, there's a whole range of things you can do, and you can do it all at once. When you go for exploration, you have to have goals that become goals for a generation. That's how America got to the moon, with Apollo,

and in a sense, that's the declaration made by the President earlier this year. We in Europe have to work out how to do the same thing if we're going to be taken seriously in exploration. Otherwise, I'm afraid, we will not play the role we could play. It's theirs for taking. I mean, we can step in and do something, but we have to get our act together. The last thoughts come from Charles Elachi, director of the Jet Propulsion Lab, and Ed Weiler, NASA's associate administrator for Space Science Enterprise.

These two administrators are still also very much scientists, and like David Southwood, they look forward to many years of theory-smashing data from Cassini-Huygens, perhaps stretching far beyond its planned or nominal four years at Saturn. Here's Charles Elachi.

Four years is the baseline. Right. But if everything goes nominal, and we'll have to wait and see what happens in the next couple of years, we can extend it by another four, five, or six years. So there's enough fuel on board the spacecraft to go significantly beyond that time.

As a matter of fact, we are starting now, you know, the team is starting to think, you know, about assuming things go nominal, particularly we know after today, if the propellant we don't consume, the nominal we consume, the amount of propellant, start thinking what do we start doing four years from now? Because you need to start planning it from now, you know, on doing that. And we need to make sure we have the flexibility that if there are any discoveries which happen, that we'll be able to adapt, you know, the mission so we can address those discoveries. So one exciting time, at least in my perspective, in my limited

perspective, will be that when we get the first pass over Titan with the radar where we get the surface images and possibly with the cameras, infrared, we're going to suddenly learn something completely new, and it's going to surprise us. No matter what model we develop, we're going to find that something is different. And then we have to start thinking, do we get some future flybys to make sure we address some of those issues? Now, of course, it all depends on headquarter funding, those extended missions, but I'm sure there will be sympathetic ear, both in Europe as well as in the U.S. for that. Right. Charles, I just disagree with one thing you said, if there are going to be discoveries.

Well, sorry, maybe I should have said that. When there will be discoveries. That's a good point. The mission baseline is based on the textbook that we brilliant humans have written on Earth about how Saturn is going to be. If we've learned anything from exploring Mars, exploring the universe,

the universe doesn't tend to read our textbooks, despite the arrogance we place on the universe. So Saturn will surprise us. There will be discoveries. Exploration creates discoveries, and science is the understanding of those discoveries. There will be discoveries, and I will bet you, not long into this mission, we'll be rethinking the second, third, and fourth year,

and there'll be plenty to keep us busy in the fifth and sixth and seventh year, and I'm sure if the science justifies it, there'll be money to pay for it. By the way, Associate Administrator Weiler will be our special guest on next week's Planetary Radio. He is soon to become director of the Goddard Space Flight Center. We'll continue to report on the Cassini-Huygens mission, but for much more in-depth information, including those stunning images, visit planetary.org slash Saturn. I'll be back with Bruce Betts and What's Up,

right after we again visit Emily at Titan. I'm Emily Lakdawalla, back with Q&A. Saturn's moon Titan is very cold and lies in a part of the solar system that contains lots of volatile materials like nitrogen, methane, ammonia, and water, so it has a thick atmosphere. Why don't any other outer solar system moons have a thick atmosphere? Some of them are just too cold. Neptune's moon Triton and the outermost planet Pluto both have very thin atmospheres, but most of the materials that

would make up an atmosphere are frozen out as ices on their surfaces. The giant moons of Jupiter are closer to the sun and a little bit warmer than Titan, but they are buried inside Jupiter's enormous active magnetosphere, which whips any air off the moons and into Jupiter's plasma environment. So Titan is in a Goldilocks location. Not too hot, not too cold, not too active. Just right for a thick atmosphere that contains lots of organic chemicals. What else is buried under that atmosphere? We'll have to wait for the European probe Huygens to visit its surface to find out. Got a question about the universe? Send it to us at planetaryradio at planetary.org.

And now here's Matt with the Director of Projects of the Planetary Society, Dr. Bruce Betts. Bruce, I hope you had a great Fourth of July. Yeah, hunky-dory swell. By the way, aren't we kind of pushing our luck here? Two successful rovers on Mars and an incredibly successful orbital insertion at Saturn, all in the space of about six months? No. That's my official answer. It's just brilliant engineering and science, right?

It is. It is. An awful lot of work went into those things. There's some luck, too, but an awful lot of effort. But, yes, a huge, huge, huge thing going into orbit around Saturn. A big moment. The one that it all depended upon to do the glorious science mission ahead of us. And the science has started to roll in, as we've just heard on this show. Indeed. Cutting edges. We always are.

And I was at JPL part of the time. You were someplace else for Cassini. I was. I was at the event that JPL held at Pasadena City College, where they shoved friends, family, and random other people like me. Much joy, much giddiness. Well, we have lots of reason for giddiness here on What's Up, of course, in addition to the great success of Cassini this week, because it's time for What's Up. What have you got for us? Exactly. Far more exciting than these pesky orbital insertions.

Come out there in the evening, look at Jupiter. You probably have. But if you haven't, get out there, look at it. Preferably take some binoculars, take a small telescope, check it out. If you have a small telescope, you look at it. Or even a big one, you will see some of its moons. Four largest moons, Galilean satellites, will look like little tiny dots all lined up in a row. Some of them might be behind Jupiter or in front of it, so you may not see all four, but you might.

So give it a try. Also, you can see if you're up before dawn, you can see Venus looking extremely bright in the east. And I'd mention Jupiter, our friend, up high, brightest thing in the west in the evening. Other things are a little tough to see, but you can give your shot at looking low on the horizon after sunset for a wee bit of Mars. What do you think, Matt? I think it's a beautiful solar system. Thank you.

All right, moving on to this week in space history. 25 years ago, Matt, 25 years ago, July 9th, 1979, Voyager 2 flew past Jupiter, giving us fabulous insights into that system. Oh, exciting. Let's move on. Random Space Facts! Did you know, Matt, we've been focusing on the ring, Saturn?

Beautiful new pictures. And the rings of a planet pretty much always fall inside what's called the Roche limit. The Roche limit is the distance away from something like a planet, where if you get something coming within that distance, it tends to get ripped apart by a differential gravity thing going on. So that's why you get the broken-up rings inside the Roche limit and most satellites forming outside that limit. The Roche limit tends to apply to a very weak, basically a liquid-type situation,

so you can get satellites just inside it, but not a whole lot. All right, let's move on to the trivia contest. Last week, we asked you a question. How did we do? Well, as usual, we did great. We're getting new listeners and lots of our longtime listeners. We even had a contact from Sean who said, you know, he doesn't want to enter the contest every week, but like a lot of other people, he thinks, he's still out there listening every week

and probably happy to hear lots of other people winning T-shirts. This week, the winner is Howard Clayton. Howard Clayton came up with the right answer, and that was to your question regarding the X-15. Yes, what company was the prime contractor on the X-15 project? Well, Howard of Dickinson, Texas, it was North American aviation, which of course later became Rockwell and then got absorbed into Boeing. So Howard, congratulations. We'll get that shirt out in the mail to you as soon as we know what size you want. We'll check with you about that. What have you got for us next week, Bruce? All right. The trivia question this week,

the thin F-ring of Saturn is held into place, kept thin, it turns out, by what are called shepherding moons. There's one on each side of the ring that tend to keep it where it is in its thinness. What are the names of the shepherding moons of the F-ring of Saturn? Go to planetary.org slash radio to find out how to enter our contest and win the glorious Planetary Radio t-shirt. The envy of all your friends. And do try to get that in to us by noon Pacific time on Thursday, July 8th, so that we can make sure that you are part of this week's contest. Shepherding Moons, I think of that big sheepdog that used to punch in on a time clock in Warner Brothers cartoons.

That's actually what one of them looks like. And what I didn't mention is that they knew before Cassini that the Siren's Rings were made up of lots and lots and lots of particles, but it looks like any data is telling us they're actually sheep. So a whole shepherding moon thing, much more appropriate than we realize. Bah. Say goodnight, Bruce. Alright, everybody, go out there, look up in the night sky, and think about all the radio waves that are passing through your body right now.

Thank you. Goodnight. Keeping me warm. That's Bruce Betts, the Director of Projects for the Planetary Society, back with us as he is every week for What's Up. That's it for this week, except for a housekeeping note. Those of you who like to listen to us in the MP3 format can celebrate a little. All of our archive shows are now available in this popular format. Just visit planetary.org slash radio to access the directory.

Back with NASA's Ed Weiler next time. Take care, everyone.