09/15/2017

A Farewell To Cassini, Our Friend At Saturn

34:56 minutes

cassini
Cassini’s descent into Saturn’s atmosphere. Credit: NASA/JPL

This article is part of our special coverage of Cassini. Listen to one of the interviews Science Friday conducted with the Cassini team and marvel at the astounding images the orbiter took of Saturn and its moons. Plus, did you know the Cassini team has their own choir? 

NASA scientists are pouring one out for the Cassini orbiter. On Friday the orbiter completed its final mission: plunge into Saturn’s atmosphere. The craft tasted the atmosphere’s chemical contents, then succumbed to the heat and pressure of the descent.

Cassini wasn’t the first visitor to Saturn, but it’s the first to stay for an extended period. In the 13 years since it arrived, we’ve seen breathtaking photos, puzzling chemistry, and data to indicate astonishing things: the moonlets and propellers of Saturn’s rings, the methane seas of Titan, and the geyser-spewing, ice-covered ocean of Enceladus.

Cassini helped discover more than half a dozen previously unknown moons of Saturn. It gave insights into the planet’s seasons and spin. Plus, it delivered a photo of Earth from Saturn that builds on the legacy of Carl Sagan’s pale blue dot.

But the end of the mission is also the end of an era. Cassini was the last of the “big” probes to other planets, before NASA switched to smaller, more focused, and cost-efficient missions.

Science Friday has covered Cassini since its launch in 1997, and now it’s time to meditate on its end.

Producers Chris Intagliata and Christie Taylor report from NASA’s Jet Propulsion Laboratory (JPL), where mission scientists observed the last ping of signal from the orbiter. Plus, Ira talks to project scientist Linda Spilker, JPL senior research scientist Bonnie Buratti, and Jonathan Lunine of the Cornell Center for Astrophysics and Planetary Science about the legacy of the mission, the spectacular science it brought back, and the new mysteries it uncovered.

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Segment Guests

Linda Spilker

Linda Spilker is Cassini Project Scientist at NASA’s Jet Propulsion Lab in Pasadena, California.

Bonnie Buratti

Bonnie Buratti is Senior Research Scientist at NASA’s Jet Propulsion Lab in Pasadena, California.

Jonathan Lunine

Jonathan Lunine is a Cassini mission scientist and Director of the Cornell Center for Astrophysics and Planetary Science at Cornell University in Ithaca, New York.

Christie Taylor

Christie Taylor is an associate producer for Science Friday. Her day involves diligent research, too many phone calls for an introvert, and asking scientists if they happen to have an audio recording of their research findings.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. The tweet from NASA this morning had the tenor of a death notice. It read, Earth received Cassini’s final signal at 7:55 AM ET. Cassini is now part of the planet it studied. Thanks for the science. Grand finale.

Yeah, scientists are marking the end of a life-changing planetary mission, NASA’s Cassini orbiter at Saturn. Cassini plunged to its death this morning and melted into the atmosphere of Saturn. And armed with instruments to photograph, probe, measure, and relay everything it could see and feel back to Earth, Cassini’s 20-year journey revealed unknown treasures of Saturn and its moons.

Intricate rings and storms of Saturn came into sharp view. It dropped the Huygens probe under the mysterious haze of Titan. Revealed the life bearing potential of Enceladus. It even swung by Venus a few times on its way there.

And now Cassini is no more. It crashed into Saturn at a speed of roughly 78,000 MPH, vaporized within a couple of minutes, just as NASA planned. The probe sent back data to the very last moment of its life. 30 seconds longer than expected.

Science Friday producers Christie Taylor and Christopher Intagliata were on the scene at JPL and Caltech in Pasadena at the very end, along with hundreds of mission scientists and engineers. Christie joins me now from KPCC in Pasadena. Welcome.

CHRISTIE TAYLOR: Hi, Ira.

IRA FLATOW: What was the mood like? Was it joyous, was it somber, was it both? A little, you know–

CHRISTIE TAYLOR: It kind of ebbed and flowed. And some of it was sleepy also, because it started at about– people were gathering at 4:00 AM, 3:00 AM, earlier. But this was the lot of Caltech where the science team was assembled. It was very convivial. A lot of people who hadn’t seen each other in a while.

There was a lot of talking and laughing. And then as the moment approached, it got increasingly quiet, somber, a lot of waiting. And there was a feed from Mission Control, sort of this whole time. When the announcement came that signal had been lost, then everyone applauded. So– but you also saw people wiping away tears. So mixed bag.

IRA FLATOW: I heard that GPL hired a grief counselor, is that right?

CHRISTIE TAYLOR: I haven’t been able to confirm that.

IRA FLATOW: Oh, wow.

CHRISTIE TAYLOR: But it might have been useful.

IRA FLATOW: Yeah. And this was planned to happen, right? This was not just an accident that it crashed into the planet.

CHRISTIE TAYLOR: Right. The key words are planetary protection. And in this case, it’s moon protection. So we had Enceladus and Titan, two bodies that look very promising for having life on them, which means you don’t want to get earth microbes on them, which Cassini could have been bearing. So as it was running out of fuel, the engineers didn’t want to risk the small but significant chance that it could crash into either of those moons. So it seemed that Saturn was a fitting and poetic end.

IRA FLATOW: Yeah, they didn’t want to contaminate the moons in case there was microbes from Earth on it.

CHRISTIE TAYLOR: Right.

IRA FLATOW: You were watching the loss of signal with the science team at Caltech. Give us an idea of who was in the crowd, how big the crowd was.

CHRISTIE TAYLOR: Well, it was almost 1,000 people, it sounds like, which they were in the Beckman Auditorium, and then they were spilling out onto the lawn. They had these great big screens up again.

But it wasn’t just the scientists, though. I would also note that it was a very international crowd of scientists. So I talked to scientists from Finland, from Germany, from France, who have all had their hands on Cassini data over the years. But it was also graduate students who were just getting their first– writing their first papers using Cassini.

And then there were all the kids of the scientists. So there were all these college age folks running around. And scientists would point to them and say, see them, they were three years old when Cassini launched, or when they watched Cassini launch.

So really, lots and lots of people, all with– as you’ll hear from the audio we gathered, with a significant time and emotional investment in this mission.

[AUDIO PLAYBACK]

– Do we cheer or do we–

– I don’t know.

– –go into silence? Lee Wigglesworth. We delivered the helium magnetometer. Get a little bit of signal coming back up.

– My name’s Mo Roy. I work with the cosmic dust analyzer instrument. When Cassini reached Saturn, this kid here was just a year old.

– Still going. It’s hanging in there.

– It hangs on.

– Had a good heartbeat, that’s why.

– Shawna Santos. I was on the operational navigation team. A lot of hard work we all put together. I remember Saturn orbit insertion. We were all super excited together. We were waiting for that first signal. And it’s just such a beautiful feeling, you know. It’s just– there’s nothing like it in the world.

– My name is Norbert Krupp. Yeah, it’s very emotional, I must say. I mean, I’m in the mission for nearly 21 years now. So I had some of this hardware in my hands. I calibrated this instrument. And it was flying around Saturn for almost 13 years.

[PA ANNOUNCEMENT] We have lost the signal.

– We have lost the signal.

[APPLAUSE]

– Just heard the signal from the spacecraft is gone. And within the next 45 seconds, so will be the spacecraft. Congratulations to you all. This has been an incredible mission, an incredible spacecraft, and you’re all an incredible team. I’m going to call this the end of mission. Project manager off the net.

[APPLAUSE]

[END PLAYBACK]

IRA FLATOW: Wow, Sounded mixed, you’re right. It was bittersweet. Thank you very much, Christie.

CHRISTIE TAYLOR: Thank you, Ira.

IRA FLATOW: Christie Taylor is our producer here, and she was reporting from the studios of KPCC in Pasadena. And if you follow Science Friday, we’re now in 26th year. You know, we’ve been covering Cassini’s journey since the very beginning with new discoveries, both exciting and puzzling from day one.

And in a moment, you’re going to reconnect with some of the scientists we’ve talked with over the years. But first, to warm you up, a remembrance of some of the amazing moments of Cassini’s career as heard on this program.

[AUDIO PLAYBACK]

– We’ve seen some of the familiar things with brand new clarity. And it’s just like seeing an old friend again in a new light. And that’s got us all very excited.

– And there’s an interesting moon of Saturn called Titan. And you’re going– are you going to be looking at Titan?

– Oh boy, are we going to be looking at Titan. Titan is going to enjoy a scientific assault.

– Are the rings the main target of this mission?

– Ah, well, from my standpoint, yes.

– Tell us about this strange object.

– Well, it is quite bizarre.

– The headlines are screaming all about possible life on Titan. Is that a little premature? It’s hard to hear a scientist say, this is the most exciting thing I’ve ever worked on.

– This is, for sure. The plumes on Enceladus are the greatest thing I’ve ever been involved in.

– You better believe there’s excitement. Just a few minutes ago, they released the very first image from Huygens. It’s been just an unbelievable day of tension and excitement and anticipation and panic and everything else, but–

– This is really just the tip of the iceberg. And there’s going to be an immense amount of data. Nothing like we’ve ever seen.

– You have to see this picture.

– It’s definitely not a boring place.

[WIND SOUND]

[END PLAYBACK]

IRA FLATOW: And that last noise was the bow shock, a sort of shockwave experienced by Cassini as it entered Saturn’s magnetosphere way back in 2004. And those were Cassini mission scientists Linda Spilker, Carolyn Porco, Jonathan Lunine, Bonnie Buratti, plus NPR Science Correspondent Richard Harris.

And here to reminisce in person, some of the voices that have joined us to celebrate Cassini over the years. Linda Spilker, Cassini project scientist. Excuse me, Bonnie Buratti, senior research scientist at JPL, Jonathan Lunine, mission scientist and director of the Cornell Center for Astrophysics and Planetary Science. All three join us from the studios of KPCC in Pasadena. Welcome to Science Friday.

LINDA SPILKER: It’s great to be here, Ira.

JONATHAN LUNINE: Great to be here, Ira.

BONNIE BURATTI: Great to be here.

IRA FLATOW: Your thoughts– your thoughts at this moment?

LINDA SPILKER: Well, I think this is a rather bittersweet moment. It’s sort of sad to lose the spacecraft and see the breakup of the Cassini family. And it’s both an ending and a beginning, as these people go on to work on other projects, the engineers and the scientists. But also, I have a tremendous sense of pride in working on this mission for almost 30 years. Basically, from the very beginning until the very end.

IRA FLATOW: Jonathan, how do you feel?

JONATHAN LUNINE: I feel a certain sense of relief this morning, because I knew– we all knew we had to go through this. The spacecraft had finite resources and the day would come. And that was the day. It was hard to go through it. Now Cassini is history, but we’ve got all this fantastic data to work on.

IRA FLATOW: Any other comments about–

BONNIE BURATTI: Well, I really feel that I’ve lost a part of myself, because when you are in orbit with a spacecraft around a celestial body, you feel that that spacecraft is an extension of your own senses. It’s like you are there. It’s your eyes and your ears. In fact, it’s better because you can see in the infrared, the ultraviolet. And when Cassini died, I really felt that I lost a part of myself. And all the scientists, I think, felt that way. There’s no human presence anymore around Saturn. And there has been for 13 years.

IRA FLATOW: And Cassini was sampling. I mean, it was sending back data right to the very end, was it not, both in the last few dives before its death and as it fell into the atmosphere? What kind of data? What might that data reveal to us? Jonathan [INAUDIBLE].

LINDA SPILKER: Well, we had 22 orbits in the grand finale. And we were probing the interior of Saturn, trying to reveal through its gravity and magnetic field what that might be like, measuring the mass of the rings, composition of the ring particles, and sampling the atmosphere. And even on that very last plunge, till the final second, we were sending back data from Cassini.

JONATHAN LUNINE: I think it’s important to note also that those 22 orbits took Cassini to a place that it had really never been before. These orbits were so different from the ones that were used to explore the moons of Saturn, Titan, the magnetosphere, seeing the rings from outside the area of the rings. To actually plunge between the rings and the atmosphere as part of this ending process gave us such remarkable science, because it was such a different view.

IRA FLATOW: And the last pick– I’m sorry, go ahead.

BONNIE BURATTI: Yeah, I would admit that the planet and the rings and the magnetic field are really the endgame. But I want people to remember the little guys. Right before the proximal orbit, before our daring dive, we got these great views of all these unique and weird little moons of Saturn. That they have little skirts, these little like tutus of ring debris around them. And that’s a whole new mission that we kind of got as a bonus as part of this end game.

IRA FLATOW: Something called Peggy in the rings?

LINDA SPILKER: That’s one thing– yeah, that was observed at the very end.

IRA FLATOW: And the rings of Saturn– I remember going back in the day when Voyager went by Saturn, seeing the first time how weirdly shaped and interestingly shaped the rings were.

LINDA SPILKER: Yeah, I worked on Voyager and it was just amazing. We were expecting just broad sheets of bland material. And to see the detailed structure, what we call like the grooves on a phonograph record, it was remarkable.

IRA FLATOW: Bonnie, when we talked to you in 2005, the plumes on Enceladus were just coming into view. And that was– we heard earlier saying, it was the most important work you were involved in. What made it so groundbreaking?

BONNIE BURATTI: Well, because it was really the first time we’ve seen massive cryovolcanism. That is volcanoes that have water ice as part of them in the solar system. There were other little plumes that we found, more like jets that were found on Triton, the large moon of Neptune. And of course, there was the silicate– sulfur silicate volcanoes on IO. But we hadn’t seen anything like this before. And we’ve just learned so much more about how they behave and how they vary. And it’s really been quite a discovery.

IRA FLATOW: Why did we go looking for geysers on Enceladus in the first place?

BONNIE BURATTI: Well, because Enceladus was this object that was– it was almost like a winter wonderland. It was covered in fresh snow. We knew that from Voyager. Like Linda, I was also involved on Voyager. And part of my thesis, I really looked at that. And was always mesmerized and knew that there was something there, but we didn’t know quite what. And we really found the smoking gun at the very first part of the mission, the Cassini mission.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from PRI, Public Radio International. Talking about the first and the last days of the Cassini mission, with Linda Spilker, Bonnie Buratti, and Jonathan Lunine. And about the family that– well, we’ll get into that a little bit later, how close to the family after three decades of working together.

So Jonathan, what kind of life do we think Titan could possibly support if the liquid is all methane instead of water?

JONATHAN LUNINE: It would have to be extremely exotic. It would have to have a chemical basis that is completely different from that of life on Earth. All of the biological molecules that underlie life– DNA, proteins made of amino acids, and so forth, none of that will work in liquid methane.

And so if chemistry has evolved within these methane seas to something that we could call life, the molecules that are the basis of that life would have to be completely different from our own. And it’s really hard to speculate on what those might be, because having only one example of life, and that’s Earth life, it’s very difficult to extrapolate.

IRA FLATOW: Why would there be such a different kind of life there? How could such a world come into place?

JONATHAN LUNINE: Well, first of all, we don’t know if there’s life in the seas of Titan. Cassini’s great discoveries on Titan included, and I would have to say first and foremost, the fact that these methane seas exist. And Cassini, of course, discovered the seas in 2006, 2007.

But it was in the very last portion of its mission over the last three years or so that we’ve been able to use the radar to not only map the depth of the seas, but to know the composition. And the composition really is mostly methane, along with a few other organic molecules. Now, methane is so different from water in terms of its properties as a liquid that molecules that are dissolved in methane have a very different way of interacting with the liquid than they do for water.

And so it has to be different if there’s life. And that, of course, is the big caveat. We do not know. One would have to go back to Titan, look for evidence of life as a test for the limits over which life or biology can exist in the cosmos.

IRA FLATOW: Now, Linda, I know you’re a ring scientist at heart. And are we learning everything we had hoped for about Saturn’s rings after we got a tantalizing glimpse from Voyager?

LINDA SPILKER: We’ve learned so much about the rings. And the grand finale orbits added to that, because we were basically taking a magnifying glass to the rings, looking at much higher resolution than we’d ever seen before. Seeing clumpiness and streakiness as the particles are grouping together.

And I think what’s really new with these orbits is we’re actually directly sampling the composition of the ring particles for the very first time with our cosmic dust analyzer. And ultimately, getting the mass of the rings, which is important for their age. We think if you could scoop up the ring particles, they’d be about the size of Saturn’s moon Mimas. And if they’re more massive, perhaps they could have formed maybe as early as when Saturn formed.

And less massive, it’s more likely that perhaps a comet or a moon, something got too close to Saturn, torn apart by Saturn’s gravity, going on to form the rings. And there’s a lot more. I’d love to get really, really close and watch how the ring particles collide with each other, how they stick together and form these objects that can grow into the propeller features and other aspects of the rings.

IRA FLATOW: It’s so mysterious. We’re going to take a break and come back and talk lots more about Saturn, its rings, its moons. Stay with us. We’re talking with Jonathan Lunine from Cornell University, Bonnie Buratti at JPL, and Linda Spilker, a Cassini project scientist. We’ll be right back after this break. Don’t go away.

This is Science Friday. I’m Ira Flatow. We’re continuing a farewell to Cassini, NASA’s probe to Saturn, which decisively ended its mission this morning, vaporized into the atmosphere of Saturn. And we were talking about life on some of the moons of Saturn. We’re talking about the life there on Saturn, possibly, life on the moons.

But one place that’s really intriguing is Enceladus, is it not? I mean, that’s someplace we hear more about it, of the possibility of finding life.

JONATHAN LUNINE: It is. In fact, Cassini not only discovered the plume of Enceladus, but it discovered an ocean underneath the surface, an ocean made of liquid water. And the remarkable thing that Cassini was able to do was to fly through that plume seven times and measure the composition of the gas and the grains, essentially to taste them.

And we know now that those grains are made of salt water, the largest ones are. And so they’re actually samples of the seawater from under the surface. And all of the things that Cassini measured tell us that this ocean is habitable, that it can support what I would call conventional microbial life. Life like we find here on the Earth.

But what Cassini could not tell us is whether that ocean is actually inhabited. And so it left us with this tantalizing pointer to a place, Enceladus, where indeed life could exist underneath the surface. And we need to go back and find out if it really does exist there.

IRA FLATOW: Do we have plans to go back and do that?

JONATHAN LUNINE: There are no fixed plans. There are a number of proposals for doing so. Some of us here have been involved in one of those. And the remarkable thing is that because the plume really does have ocean material coming in it, that’s coming out from inside Enceladus, we can actually search for life by flying through that plume again.

But we would need to do it with modern instruments, instruments that have been designed today, that have greater power than Cassini’s. And we would be able to detect the signs of life. Again, just by flying through the plume, as Cassini did.

IRA FLATOW: Of course, unless we send another spacecraft to find a new way– or find a new way to observe it from afar, the last clues scientists have to work with are already sitting in the data packets that are awaiting analysis from Cassini. But for the people who’ve been part of this mission, and some of them for nearly 30 years, they are not just saying goodbye to a spacecraft or a source of data. They’re also saying goodbye to a community, a family, really, they’ve been building since the mission was a twinkle in NASA’s eye. Sci Fri’s Christie Taylor got up close and personal with the Cassini family members and had this sound portrait.

CHRISTIE TAYLOR: The first thing you need to know about flying a spaceship is that it’s not your usual 9:00 to 5:00.

EARL MAIZE: It can be Christmas Eve. It can be 3:30 on Sunday morning.

CHRISTIE TAYLOR: Earl Maize is Cassini’s program director. He and the rest of the team worked those odd hours because they’re slaves to the gravitational dance of Saturn and its moon Titan.

EARL MAIZE: When we get with the planets, we have to go where they are.

CHRISTIE TAYLOR: This means lots of nights and weekends with mostly the same people for 20 or 30 years. The Cassini team, Earl says, is like a second family. Veteran team members vacation together, watch each other’s dogs, and know each other’s spouses and kids.

EARL MAIZE: We’ve had a lot of births. My daughters essentially grew up in and around JPL. Watching those kids grow up has been quite amazing as well.

TRINA RAY: Imagine you go to work every day in your neighborhood and you see these people for 20 years. And you work with them. And you know nobody’s leaving, so you have to get over the rough spots, because you’re going to be working together for 30 years, or 20 years.

CHRISTIE TAYLOR: Trina Ray is another member of the Cassini family. She studies Titan, Saturn’s methane-rich moon.

TRINA RAY: And I have been on the Cassini mission for 20– oh my gosh, 21 years.

CHRISTIE TAYLOR: That’s three Saturn seasons, just shy of a year for the gas giant. And for just as long, she’s been part of one of the Cassini family’s longest standing traditions, the Cassini Virtual Singers.

CASSINI VIRTUAL SINGERS: (SINGING) A planet of our own, a moon with atmosphere.

IRA FLATOW: Yes, it’s a singing group, formed in 1997, just after the orbiter was launched on its way to Saturn. In that 20 years, they’ve parodied everything from Little Shop of Horrors, which you just heard, to Hamilton, and Taylor Swift. They practice at lunchtime, and everyone is welcome.

CASSINI VIRTUAL SINGERS: (SINGING) Somewhere with wings.

TRINA RAY: Well, we have the program secretary. We have scientists. We have engineers, software developers. So we have some people who are absolutely fantastic musicians. They read music. They have perfect pitch. And then we have people who have no singing ability. That would be me.

CHRISTIE TAYLOR: The group has written or rewritten over 100 songs by now, starting with Dion’s The Wanderer.

[MUSIC – DION, “THE WANDERER”]

TRINA RAY: And we called it the orbiter, because we go around, around, around, around. That kind of thing.

CHRISTIE TAYLOR: You might recognize this adaptation too, one of the most popular at JPL.

CASSINI VIRTUAL SINGERS: (SINGING) People talking without thinking, people typing without muting, people writing songs–

CHRISTIE TAYLOR: It pays tribute to the emergency conference calls that can summon the mission scientists and engineers from their slumber at any hour.

CASSINI VIRTUAL SINGERS: (SINGING) We do not dare, disturb the sound of science.

CHRISTIE TAYLOR: This, and songs like it, form the soundtrack for everyday life on team Cassini. Heard at big project meetings, mission anniversaries, and geeky holidays like Pi Day on March 14, when Earl Maize whips up a pumpkin pie with an outer planets twist.

EARL MAIZE: I make a little Saturn out of dough and put a little ring around it and plop that in the middle of the pumpkin. And so there’s a little Saturn in the middle of the pie.

CHRISTIE TAYLOR: But maybe one of the most exciting family gatherings for this crew is when the data’s coming back. Like when the Huygens probe sent back the first clear pictures of Titan’s surface.

LINDA SPILKER: Could that be a volcano? Is that a crater? What do you think we’re seeing here?

CHRISTIE TAYLOR: That’s Cassini project scientist Linda Spilker, who’s been on the mission since 1988, day one.

LINDA SPILKER: There’s tremendous excitement in the room. And it sometimes is like everyone wants to talk at once. And all of these different ideas bubble up.

CASSINI VIRTUAL SINGERS: (SINGING) 0 1 0 1 1 1–

CHRISTIE TAYLOR: And yes, there’s a song about that too.

CASSINI VIRTUAL SINGERS: (SINGING) I’m hooked on your data. Sooner or later, I hope it comes to me. Titan’s–

CHRISTIE TAYLOR: By now, Cassini and its instruments have been reduced to their elements, from aluminum to iridium, all the equivalent of dust on the wind in Saturn’s atmosphere. And the flow of data, all those zeros and ones, that’s evaporated too. Trina Ray again.

TRINA RAY: There will be no new Titan data for years, and maybe decades, maybe not in the rest of my professional career. I’m going to really miss this constant sort of burst of data from Cassini telling me something about Titan. I’m going to miss that.

But I’m also going to miss the people that I work with. We’ve been together for a long time. And it’s going to be– it’s going to be sad.

CHRISTIE TAYLOR: As the mission ends, everyone has different ideas about how well the family will stick together. A wave of retirements, for sure. And a diaspora of scientists and engineers heading to other projects at JPL or elsewhere. But Linda Spilker, the project scientist, she’s optimistic.

LINDA SPILKER: For Cassini, the final plunge is both an end and a beginning. It’s kind of like a graduation.

CHRISTIE TAYLOR: Spilker’s been looking toward the outer planets since the very beginning of her career. And she’s hoping we will get back there someday, before she herself retires.

LINDA SPILKER: What I’d really love to see is future missions to Uranus and Neptune. Take Cassini-like orbiters and send them out to the ice giants. Or even send something to land a boat into one of the Titan lakes and seas.

CHRISTIE TAYLOR: And maybe that dream will have a musical soundtrack all its own.

CASSINI VIRTUAL SINGERS: (SINGING) For it’s down to Titan I go and then on to fame. Float, drop, splash.

CHRISTIE TAYLOR: Wait, why is float before drop and splash?

CASSINI VIRTUAL SINGERS: Because we’re floating through the atmosphere and–

[INTERPOSING VOICES].

CHRISTIE TAYLOR: For Science Friday, I’m Christie Taylor.

IRA FLATOW: What a terrific look at the Cassini community. And speaking of which, we have Cassini veterans here with us. Project scientist Linda Spilker, mission scientist Bonnie Buratti, and Jonathan Lunine. Linda, you were in that piece. You sounded very remorseful a little bit.

LINDA SPILKER: Yes, well I’m not a part of the Cassini Virtual Singers, but certainly, there is remorse there with the end of the mission.

IRA FLATOW: Has the team earned the name family in your eyes?

LINDA SPILKER: Oh, absolutely. As was mentioned, I think our kids have grown up together in some sense, vacationing together. I went to see the solar eclipse with a couple of Cassini members. And have really gotten to be a close knit family.

IRA FLATOW: Jonathan, Bonnie, you agree?

BONNIE BURATTI: Definitely. Some of my best friends and colleagues are on the Cassini mission, not just at JPL, but all the science teams. We’ve been through this together and the camaraderie that’s developed is pretty intense. We are one big family.

JONATHAN LUNINE: I agree with all of that. I can’t can add any more. We are a big family.

IRA FLATOW: Cassini wasn’t equipped to answer the questions of whether there is life on Titan or Enceladus. Is there anything else it hasn’t revealed to us that you all are particularly interested in?

BONNIE BURATTI: Well, there’s one thing, one mystery, that I think we’ve left. And that is whether there are any icy moons other than Enceladus that are active. Dione, which is a much larger moon than Enceladus, has given us these little teasers about its activity. There seems to be an extinct ice volcano on it.

My colleague, Roger Clark, observed a transient atmosphere around it. There seems to be possibly little puffs coming out of it that are affecting the fields and particles instruments. But we haven’t found an obvious example of activity on Dione.

We have a lot of data. We’re going to be continuing to pore through it. And maybe we’ll know, but that is the one thing that I think we’ve left there at Saturn that we don’t really know.

LINDA SPILKER: I’d say another one, Ira, is the hexagon, this six-sided jet stream around the north pole of Saturn, two Earth diameters across. We’ve watched it. We’ve studied it. We’ve seen clouds race around like cars on a racetrack. And we still are not sure what keeps the six sides in shape.

It’s the only hexagonal jet stream on the giant planets. The south pole of Saturn doesn’t have one. Jupiter doesn’t have any hexagons. So what’s keeping this hexagon going?

JONATHAN LUNINE: And I would add with respect to the atmosphere of Saturn, there are things that Cassini can’t measure. Noble gases, for example. They’re not very sexy, but they’re really crucial in terms of understanding the formation of Saturn. If we want to measure those, we’ll actually have to go back and send a probe deep into the atmosphere of Saturn, much like the Galileo probe at Jupiter.

IRA FLATOW: This is Science Friday from PRI, Public Radio International. Talking about the final days of Cassini. Something that we don’t talk much about, but it is like many of NASA’s planetary missions. Cassini went way above and beyond its original mission goals, didn’t it?

LINDA SPILKER: It certainly did, yes. Yes, we had a four-year prime mission with goals, basically. What we didn’t find out from Voyager, we were going to do with Cassini. And we went so much farther than anyone, I think, could ever have dreamed or imagined in exploring the Saturn system.

BONNIE BURATTI: Yeah, scientists at JPL, we have this little kind of secret tally that we keep. We have this factor that says how much better is the nav team than they really say? How much better are the engineers than they really say about how long the mission is going to last?

So we all kind of know that the nav team is about eight times better as they really say. And I think with the engineers and how long the mission lasts, it’s at least three times as long. It’s not only Cassini, but it’s the Mars Science Lab and all the Martian missions. And the scientists, we secretly have our little keep tabs on that and know.

IRA FLATOW: And people don’t realize today how much of an international venture it was.

LINDA SPILKER: Absolutely. I think that’s one of the strengths of Cassini. All of these scientists that have come together. You know, ESA built the Huygens probe. We’ve had collaborations also with the Italian Space Agency providing scientists and parts of the instruments on the spacecraft. I think that’s really a strength and something, hopefully in the future, we’ll see more missions with this kind of international collaboration.

IRA FLATOW: Are we going to see one that’s such a super duper machine as Cassini was?

JONATHAN LUNINE: It’s really hard to know. Cassini was such an extraordinary machine and operated so well, and it was remarkable in being able to follow up on its own discoveries with even more discoveries. So it was hard last night. It felt– or this morning. It felt like the science team had been put safely onshore on a port. And the crew went out and scuttled this beautiful ship, as they had to do. We’ll see if anything matches Cassini in the future.

IRA FLATOW: You think you’re going to find it hard for all the engineers and all the people involved to adjust to different life now?

LINDA SPILKER: Well, I think there are a lot of other missions for the engineers to work on, other places like Europa Clipper, to help out with the Juno mission, Mars 2020. So they’ll be fanning out and taking those experiences forward.

And the Cassini scientists say they have decades more of analysis they could do. And who knows how many PhD theses might be buried in the data when you start to look at it carefully. So we have funding for another year for the scientists to continue to look at the data, and then calibrate it, and then save it for future generations.

BONNIE BURATTI: I think scientists are really going to be busy with this data. I think of Mark Showalter, who discovered Pan, one of the moons that orbits in one of the gaps in the rings of Saturn. He discovered it 10 years from Voyager data after the mission. So we scientists have just skimmed off the cream. There are, as Linda said, theses to be created from this data. We’re going to be looking at it for a very long time.

IRA FLATOW: Thank you very much. I want to take time to thank all of you for spending time with us. Joining me from the studios of KPCC in Pasadena, Linda Spilker, Cassini project scientist, Bonnie Buratti, senior research scientist at JPL, Jonathan Lunine, mission scientist and director at the Cornell Center for Astrophysics and Planetary Science. Congratulations to all of you on a great mission.

LINDA SPILKER: Thanks, Ira.

IRA FLATOW: You’re welcome. Charles Bergquist is our director. Our senior producer, Christopher Intagliata. Our producers are Alexa Lim, Christie Taylor, Katie Hiler. Our radio intern is [? Sushmita ?] [? Potter. ?] Rich Kim is our technical director. Sarah Fishman and Jack Horowitz are engineers at the controls here at our production partners, the City University of New York.

One last thing before we go, here’s the Planetary Society’s Robert Picardo, with his own tribute to Cassini.

[MUSIC PLAYING]

ROBERT PICARDO: (SINGING) Good bye, Cassini, your mission’s fini. Bravo, Cassini, have some linguine. You showed us Saturn’s rings and lots of pretty things. Huygens probe took the dive early 2005. Landed on Titan, it was excitin’. Your mission never failed to surprise. Dazzled our eyes. Now dive to Saturn, vaporize.

[APPLAUSE]

IRA FLATOW: I’m Ira Flatow in New York.

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About Christie Taylor

Christie Taylor is an associate producer for Science Friday. Her day involves diligent research, too many phone calls for an introvert, and asking scientists if they happen to have an audio recording of their research findings.