Planetary Radio: Space Exploration, Astronomy and Science - Cassini Project Scientist Linda Spilker’s Last Appearance Before the Grand Finale

Episode Date: August 23, 2017

It’s the Grandest Finale. The spectacular Cassini mission’s exploration of Saturn will end on September 15th when the spacecraft plunges into the planet. Cassini Project Scientist Linda Spilker is back with one last mission update.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Linda Spilker's last Cassini update before the grand finale, this week on Planetary Radio. Welcome, I'm Matt Kaplan of the Planetary Society with more of the human adventure across our solar system and beyond. Did you see it? I have just returned from Southern Illinois University Carbondale and the Great American Eclipse. Much more about my amazing experience next week, but I want to congratulate all the listeners who joined me on the path of totality and thank those of you who wished me well. I'll have a bit more to say when we join Bruce Betts later in this streamlined edition of Plan Rad. I've got exciting news to share before we visit with the Cassini Missions Project scientist.

Linda Spilker will be one of our guests on the evening of Monday, September 18th, when KPCC Southern California Public Radio and the Planetary Society celebrate the mission with a special live show at Caltech in Pasadena. That's just three days after Cassini ends its spectacularly successful mission at Saturn by plunging into the ring planet. Tickets

are free, but you must RSVP. Reservations can be made at scpr.org slash events. We'll be streaming the show live for those of you who can't join us in person. That's Monday, September 18th, beginning at 7.30 p.m. Pacific, with information and reservations at scpr.org slash events. It's on this week's show page, too, at planetary.org slash radio. With less than a month left before the spacecraft's fiery end, Linda, once again, join me at Planetary Society headquarters. Linda, welcome back.

I'm very happy to be here, Matt. Thanks. Okay, you're happy to be here, but are you, like me, a little sad? Because this may be, probably is, our last conversation before the grand finale. Wow, Matt, you're absolutely right. It's really hard to think about the Cassini mission ending. Oh God. I mean I've been with Cassini for almost 30 years and you think about that, that's a big chunk of my career. And in fact my oldest daughter Jennifer had just started kindergarten when I started working on Cassini, and now she's married, and she has a daughter of her own. And I wonder, where did those decades go?

They flew by. It's a multi-generation mission. Absolutely. You know, we just, we talked with Ed Stone just last week, speaking of long-lived missions. Maybe Cassini is number two, at least for a planetary science mission, in terms of longevity? That might be, Matt, as of right now, but we've got new horizons that will probably keep going for a long time as well. That's true, of course. NASA just built a great spacecraft. Oh, God, yeah. And it's doing well, right? You're in good health. Absolutely. Cassini is doing really, really well. No problems at all with our grand finale orbits. There is so much for us to talk about. Now, I'm going to tease our listeners a little bit because we don't have the details to hand out yet. But there is a good chance that we will be giving everyone, including you and me, a chance to celebrate the grand finale and this entire magnificent mission very soon after the mission, maybe just two or three

days after. That would be fantastic. Well, I hope by the time this interview is available to listeners, I'll be able to provide more details. So this may be a redundant announcement, but I'm so looking forward to that because this needs to be celebrated. Absolutely. What an incredible mission, incredible science, 13 years in orbit around Saturn and really rewriting the books on the planet, the rings, the moons, the magnetosphere, Titan. We know so much more today. And you lied because it's not 13 years. It's right.

It's going to be 12 years in what, 11 months? Right, right. Oh, if we could have gone one more month, we would have ended on the 13th anniversary of launch. But more important, as we've talked about on this show in the past, you've made it through a good portion of a Saturnian year. Absolutely. Almost half a Saturnian year, two seasons on Saturn.

And that just tells you that 30-year orbital period for Saturn is a long time. So we're going to have a chance, hopefully in this event that I can't talk about yet, to look back over the mission and the significance of this mission. You did point me to an article that's available on the web. We'll put up a link to it on the show page at planetary.org slash radio, which really captures in nine topics why this mission is so significant. I don't know. Do you want to give at least a little bit of lip service to that now,

and we'll go into it more deeply later? What it addresses, Matt, is why Cassini matters, and I'll just talk about a couple of those. One of those has to do with all of the discoveries Cassini has made about this tiny moon Enceladus, only 300 miles across, liquid water ocean beneath its icy crust, and just how we would evolve in our understanding the possibility of hydrothermal vents, a salty ocean much like the Earth's, and then the big question, could there be life in the ocean of this tiny moon? And then Titan also has an ocean of liquid water, and then the methane lakes and seas. The two ocean worlds. Right, two ocean worlds, at least at Saturn. So that's one of those.

Then the second is Titan itself. Voyager saw this hazy ball, and immediately after those flybys in the early 1980s, we knew we have to go back. There's so much we want to learn about this moon, the size of the planet Mercury. So Cassini carried the Huygens probe and the Huygens probe as it parachuted down to

the surface revealed Titan for the very first time. We saw river channels, we saw sand dunes made of organic particles at the equator, lakes and seas especially at the North Pole of Titan. A world that looked so familiar, Earth-like. It had methane clouds. Methane is the water on Titan. It can rain methane that flows through the river channels and fills the lakes and seas. And so those are just two, and Cassini has done so much more about the planet itself as well as the rings, really shaping and changing our understanding of this very unique system. So glad you mentioned Huygens so that we can give well-deserved kudos to the European Space

Agency, which was responsible, of course, for that probe. Ed Stone talked about how, you know, Voyager, there was so much hope that it would be able to peer through the clouds of Titan. Didn't happen. We had to wait for Cassini for that. Not just Huygens, but you basically also kind of alluded to the radar capabilities that you brought with you to Saturn. Right. We've revealed Titan in a sense from the inside out. We've looked at Titan with the radar that can pierce through the haze to the surface, looked at the near-infrared visible wavelengths,

then further into the infrared with a spectra visual and infrared mapping spectrometer, far infrared, also in the ultraviolet. So we've been able to map the surface and measure the composition of the atmosphere. The Ion and Neutral Mass Spectrometer has flown through and tasted the atmosphere of Titan, telling us about its composition high up. And then we have gravity measurements telling us about the inside of Titan, finding that liquid water ocean and what Titan is like on the inside. So the incredible suite of instruments, including fields and particles to measure the interaction of Titan's atmosphere with the magnetosphere, have really revealed Titan as a fascinating world in its own right.

We've got to go back, right? Absolutely. Enceladus as well. Enceladus, Titan, and maybe even a probe like Galileo had, but deep into Saturn's atmosphere instead. While we're talking moons, we could spend the entire conversation, of course, just on them. But there is one, one little guy with a name drawn from Inuit mythology. Do you know what I'm talking about? I'm not going to try to pronounce it. I want to hear you say it. No. Which one is that, Matt?

Oh, gosh. I didn't even write down the name. It's a little tiny, like 14-kilometer moon that- One of the outer moons of Saturn. Probably a captured object. Oh, very dark, apparently. Right, right. And we've been studying these little tiny moons with the Cassini cameras in particular, and trying to figure out how fast they rotate, how bright they are, and even getting some ideas about their shape. And then there are those shepherd moons that Cassini has revealed, the ones that keep the rings in shape. Right. It's just incredible with our ring grazing orbits right before the start of the grand finale, we got close-up looks at some of these fascinating tiny moons. We got a really good look at Pan, which is orbiting in the Encke gap, Daphnis in the Keeler Gap, and then Janus and Epimetheus, Atlas, Pandora,

and the list goes on to really get high-level detail to see what the surfaces look like. Some have lots of craters. Others have smooth portions of the surface. And then, of course, some of them have these skirts of material that look like just a giant ring of material around the equators of these tiny moons. And these are the ones that are closest to the rings or in the ring gaps, and they're actually accreting ring particles, but just around their equators. Since we're talking about the rings, that's a good part of what this grand finale, these last orbits have been about, right? Right, right. Some of our closest views ever of the rings. When we're in the ring-grazing orbits, we could look at the A-ring

and the outer rings, get a really good look at these propeller objects, actually be able to see not quite the object itself, but these two arms and where there's particles and where there might be gaps. These little tiny moons, probably only a kilometer or less in size, are trying to open up a gap. And they create these two arms of a propeller that are like the start of a gap, but they're not quite big enough to finish the job. These objects are like the early planetesimals from which the planets in the solar system formed. So by studying how the propellers interact with the ring disk,

we're learning something about sort of going back in history, perhaps about what that disc of material from which the planets form might be like. And then as we're going into the grand finale orbits, we're getting high resolution views of the rings and seeing incredible structure. In fact, as we peer more deeply into the rings, we're seeing more and more and more detailed structure in some places. You can go online at saturn.jpl.nasa.gov and look at the raw images, especially of the rings, and puzzle along with us what could be going on. We have great views of the sea ring. We can see some of the plateaus at high resolution. I was going to

ask you about those. What are these plateaus? We're puzzled about what exactly keeps the ring particles together there because the plateaus are more dense than the ring material around them in the sea ring. And they have some interesting structures. It looks like there may be clumpiness inside of these plateaus. And we're getting views that we've never, at much higher resolution, than we've ever seen before. And we're scratching our heads too. How could we, you have this clumpiness and structure in some places and bland ring regions in other places. And what's driving

this process? We're puzzled, but we're happy. Nothing like being puzzled. Make a scientist very, very happy. Oh yeah, that's the passion, beauty, and joy, right? So plateaus, but not in the sense of plateaus here on Earth where it's a raised geological structure, obviously. But the structure that you're seeing, these have some staying power, right? I mean, we think of the rings as being really dynamic, but some of these features last for at least for a while. Right. These plateaus have been there. We saw them with the occultations with Voyager, and they're still there today. They

don't appear to move around or change much, but we're trying to figure out what keeps those particles confined. Because you would think that over time, since there are more particles in the plateaus, that they would bump into each other and slowly spread out. But they don't seem to do that. Something is keeping them confined. In some cases, maybe one edge is near a satellite resonance, and that resonance helps confine it. But in general, there are a lot of these plateaus with these edges, and there are similar kinds of structure in the Cassini Division.

The Cassini Division structure is much like the C-ring, and we're still puzzling. Why do we have this structure? And before we move on, we probably should have you remind us of what the propellers are. They're these radial structures, right? Right. A propeller is a little radial structure in the rings. It has an object, you know, maybe a kilometer or less in size, maybe a kilometer or less in size, and the gravity of that little object is trying to open up a gap around itself in the radial direction along the rings.

That's our most frequent guest, Cassini Project scientist Linda Spilker. She'll return in a minute. This is Planetary Radio. Hey, Planetary Radio listeners. The Planetary Society now has an official online store. We've teamed up with Chop Shop, known for their space mission posters, to bring you space-inspired art and merchandise. You can find exclusive Planetary Society t-shirts, posters, and more.

Visit planetly.com to learn more. That's planet.ly forward slash space shop. Hello, I'm Robert Picardo, Planetary Society board member and now the host of the Society's Planetary Post video newsletter. There's a new edition every month. We've already gone behind the scenes at JPL, partied at Yuri's Night, and visited with CEO Bill Nye. We've also got the month's top headlines from around the solar system.

You can sign up at planetary.org forward slash connect. When you do, you'll be among the first to see each new show. I hope you'll join us. Welcome back to Planetary Radio. I'm Matt Kaplan, joined once again by Cassini Mission Project Scientist Linda Spilker. So as you've been making these close grand finale passes, I think the last time you were on, we talked about on the first of these, you used your dish that Cassini has to have to communicate with Earth as a shield, right? I mean, did it turn out to be necessary? Well, you're right, Matt. We used the

high-gain antenna as a shield on that first orbit. Since we'd never flown there before, we were worried about ring particles and how many they might be. We flew through that region, and we had instruments that could detect any hits on the spacecraft, and the radio and plasma wave spectrometer essentially saw nothing. It turned out that it looked like we were in a ring particle-free zone. But what's happening is the ring particles are so tiny, nanograins, kind of like smoke particles, that when they hit the spacecraft, they didn't make that little electrical signal that the radio and plasma wave spectrometer could measure. So they're there.

They're just really tiny. And now another puzzle, what is taking the bigger ring particles and grinding them up and just leaving little tiny nanograins? And we can fly through this region and maybe we'll see one or two half micron or micron sized particles, but the, you know, the bigger particles, they're just not there. So this is good news for Cassini. Once we saw how safe it was on the first orbit, then we went ahead with all of our plans to point the cameras and point at the Earth for gravity measurements, then we could go ahead with our science. Had that region been really full of ring particles, we could have decided

on every orbit to fly with the high-gain antenna as a shield, but we didn't have to do that. Now, by the time listeners hear this program, the next, actually the first of the last five of these passes between the rings and the planet will have taken place. And I read that there is some concern, not from the rings this time, but because you're basically going to graze the atmosphere. That's right, Matt. With the grand finale orbits, we've been slowly walking closer and closer to the top of Saturn's atmosphere. And Titan is going to give us a distant nudge that will push us closer to Saturn than we've ever been before. And so we're going to make direct measurements,

sample the atmosphere, literally dip our toe in the atmosphere as we fly by Saturn. Our ion and neutral mass spectrometer will measure the composition of Saturn's atmosphere and also we'll get an idea about how dense it is. We're going to look at how often our little thrusters fire. And we think it's somewhere between 10% and 60% duty cycle. If it's greater than 60%, then we have the option to perform a maneuver and pop up just a little bit so that those spacecraft won't tumble. You mean like during that orbit or for future? For a future orbit, we have a plan.

We could literally move up just a little bit, a little bit further from Saturn. We call it a pop-up maneuver. If the atmosphere is thinner than we expect, thinner than our models predict, we could do a tiny pop-down maneuver and get close enough to really get good measurements. So we could either pop up or pop down. If we're right on the model predictions, then we don't have to do anything. So have the spacecraft's thrusters been added to the list of instruments? anything. So have the spacecraft's thrusters been added to the list of instruments? In a sense, because they have to keep us under control so that we can keep that ion and neutral mass spectrometer pointed in the direction of the atmosphere and scoop up all the molecules we can

to make those measurements. That is so interesting, and it's only going to get better and better as we go through these last five orbits. What's ahead? Give us a little preview of what we can expect leading up to the grand finale. Well, in these final five orbits, the focus is going to be on getting this ion and neutral mass spectrometer data of the gaseous atmosphere. And our cosmic dust analyzer will be looking for any ring particles that might have wandered in there or anything that they can measure with their detectors and then around that closest approach period we're going to be taking more pictures of the rings and of the planet itself radar we've got radar data of the rings as well so basically continuing to make

these really wonderful close-in measurements. And then of course on September 11th, we get another nudge from Titan. Titan is, it's a distant nudge, but it's enough that it pushes Cassini's closest approach point deep into Saturn's atmosphere. And at that point, we'll point the high-gain antenna at Earth, atmosphere. And at that point, we'll point the high-gain antenna at Earth, keep sampling the atmosphere for as long as possible, science to the end. And then once those tiny thrusters can no longer control or the atmosphere gets too dense, then we'll go off Earth point. The spacecraft will very soon thereafter burn up in the atmosphere, vaporize, and the mission will end. And we'll be watching that radio signal on the

ground, watching that. Basically, it's a strong signal, a strong peak. And when that peak drops to zero, at that point, the mission will be over. Sigh, heavy sigh. Yeah, that'll be a really solemn moment, I think. But from there is to go on and reflect back about all of the wonderful things that Cassini has done as part of Cassini's legacy. And then to, you know, move forward. Cassini, with the grand finale, it's both an ending and a beginning. It's the end of the Cassini mission, but there's a tremendous legacy of data. And as the Cassini family goes its separate ways, we'll take that knowledge that we have, whether it's science or engineering, on to other missions and to other

places. So the beginning is to go out and then take what we've learned with Cassini and use that for missions. Maybe we'll go back to Saturn with an Enceladus or Titan or a Saturn probe. I'd like to see us go on to Uranus and Neptune to go to those two worlds that Voyager flew by, and that's the only close-up data we have. Take two Cassini-like orbiters, one to each of those worlds, and continue on with our exploration of the solar system. And I know you're not alone in hoping

that we could also explore those ice giants even farther out in the solar system, does come up on this show pretty frequently. Right. There's so much. We need to compare them to what's going on with the gas giants. As we approach the end, what mysteries remain that you still hope to get a clue about? And I have one in mind here, which I'll put this way. Why doesn't Saturn want us to know how long its day lasts? That's an incredible puzzle to this day. We've gotten

these great magnetic field measurements, and we're looking for a tiny offset between the axis about which Saturn rotates and the axis of the magnetic field. All of our theories tell us you need an offset to keep that magnetic field going. And as we keep looking at the data, that keeps getting smaller and smaller. It's now less than 0.06 degrees. And it may be so tiny, we won't be able to see it. So that is an interesting puzzle.

What's going on with Saturn? That it can have a magnetic field. It has a strong magnetic field. And yet these two axes are so closely aligned together. So that may be a puzzle that will be left for a future mission, although I know there are lots and lots of ways they can look and model that data. It just might take a while. Maybe it'll take a year until we have an answer. Ed Stone talked about how happy he is to see Voyager data,

some of it nearly 40 years old, still bringing out new science. Do you expect the same from Cassini data and images? Oh, absolutely. We have incredible data, and in a certain sense, we've had a firehose of data for almost 13 years down to the earth. And we've really just sort of looked at the top level, skimmed the cream off of the data. When you really get down into the details and start intercomparing instruments, you know, there are many PhD theses in this data set,

I am sure. And people probably continue for decades more to look at the Cassini data. And especially if we're going to go back with another mission, you know, carry instruments to look for life on Enceladus, to land in a lake or sea on Titan or orbit Titan. We'll go back to the Cassini data as the ground truth, and from there, build future missions. You know, I was going to say that I am so looking forward to being at JPL with my colleague, Emily Lakdawalla, on Friday morning, August 15th, early morning. Do you remember the time? September 15th, yeah. Sorry, September 15th, a Friday.

At least in the Pacific time zone, it's like 5-something in the morning. It'll be around 5 a.m. in the morning. And we're getting a more and more precise time. Part of that time is driven by just how thick the atmosphere is in those last five orbits, and that could tweak our timing just a little bit. Okay. So, but it's around 5 in the morning, you know, maybe 5.02 or something, but around 5 a.m. we'll all be at JPL, or a group of us will be at Caltech as well, watching for that final signal as it fades away. There'll be a NASA TV program that will go with it

and anyone can watch NASA TV to see what's happening with Cassini and be along for those final moments as we go into the atmosphere. I want to say I'm really looking forward to being there. I am. It's thrilling. I'm not looking forward to the end of the mission, of course, but all things, all good things must pass.

And Cassini will have left this tremendous legacy that I think it's fair to say has made it one of the greatest planetary science missions of all time. I would agree, Matt. We have revealed so much with Cassini about Saturn and its system, and that will last for a long time. Linda, I will see you, I hope, again. I think you'll be a little bit busy and be in a very different room,

but I do hope to see you on September 15th, that morning. And then, if all goes well, maybe very soon after, stay tuned for a celebration, a post-grand finale celebration of Cassini, this magnificent mission to Saturn. I look forward to that, Matt. And I look forward to seeing you on the 15th. Linda Spilker, the project scientist for the Cassini mission, as you heard, 30 years on this mission and a long history at JPL before that, including on the Voyager mission, right? That's right. I started my career on Voyager just before launch,

all the way through the flyby of Neptune. How nice. What a great way to start your career. I'll say, yeah. And to hit the 40th anniversary of one as you reach the end of another one. Right. Two big milestones. We'll be right back for this week's edition of What's Up with Bruce Betts.

Time for the first post-Great American Eclipse What's Up with the Director of Science and Technology for the Planetary Society. Dr. Bruce Betts is back from, how do you say it, Madras, Oregon? Madras, Madras. Madras. Something like that. Yes, the thriving metropolis that's now returning to rough less than 10,000 people after having hundreds and hundreds of thousands filling the fields, including yours truly. Wow. All right. So tell me, how was the experience up there? The eclipse was amazing. We had a very, very thin cloud layer, but that's it. And so we were able to see the whole thing with the beautiful views of the Corona and prominences. And it's my first totality, as you know. So it was quite profound, enjoyed by me, enjoyed by my sons and my brother

who were there, along with presumably the other few hundred thousand people. There were a lot of logistical glitches with being in a field, but I won't bore you with them. It was still worthwhile after traffic and sanitation and other problems. Well, as you may have heard, we had a wonderful time in Carbondale, Illinois, at Southern Illinois University, Carbondale, Illinois, at Southern Illinois University, Carbondale. And more about that next week when we air Planetary Radio Live, which we did on the eve of the eclipse. Sadly, our mostly clear but hazy sky was interrupted during totality by this one cloud, this one evil cloud.

We had maybe 30 seconds. We got to see the diamond ring, but I did not see the corona. A few thousand feet north or south of us, they had apparently 100% great view. But the stadium with 14,000 people in it and me up on the stage was just in exactly the wrong spot but we it was still wonderful we got night we got about 30 seconds of totality as i said we got the diamond ring we even got shadow bands uh they had put tarps out on the field so that we could watch for them white tarps spread by girl scouts that was pretty cool It was still a fantastic experience. That's great. Now we rest. Yes, now we rest.

But before we do, what else is up in the night sky? What's left? Nothing. That's it. Hey, I also saw Venus up in the night sky. I was busy taking pictures and looking at other stuff, so I only saw Venus. But I saw it out so if you there's another total eclipse that we didn't predict you'll be able to see venus but you can also

just see it in the pre-dawn sky dominating over in the east in the evening you got jupiter low in the west and saturn more towards the south so still cool yeah so i think uh this this time let's let's go straight to the the you know, the RSF portion of this. And you've got something special, right? Yeah, we do. And I won't explain why until a moment or two from now when we get to the contest. But a few folks out there may remember that we got some very special random space fact intros from a bluegrass group out of Atlanta, Georgia, called the Possum Kingdom Ramblers. And here's one of those that they sent to us.

Okay, I will explain, as I said, in a moment. But go ahead. What's the fact? At least one more eclipse fact from this eclipse. What's the fact? At least one more eclipse fact from this eclipse. The width of the path of totality that we were both in for the August 21st, 2017 eclipse is about 100 kilometers, 100 kilometers wide, the path of totality crossing the United States in this case.

And I look forward to hearing how many millions of us were crowded in to that 100 kilometer wide swath, that path across North America. I only counted the people right around me. Was I supposed to count more? No, I thought you were going to pick up the entire path, but it's all right. We can catch it in 2024. That'll be the trivia question. Hey, let's go on to the contest.

I asked you, when is the next total solar eclipse after the one on Augustust 21st 2017 how do we do matt i'm going to zip right into this so that i can explain why we brought back the possum kingdom ramblers bambi lynn is part of that band uh out of well taxily town i think near atlanta and uh she's a long-time listener something like going on three years, a long time entrant in the contest. This is her first win. Bambi, you did it. She said July 2nd, 2019, beginning across Argentina and Chile, Tuamotu Archipelago. Pretty oceanic, except for Argentina and Chile. But yes, that is correct. Bambi, congratulations. Meow. She's kind of a kitty cat sort of a person. Bambi, we are going to send you the brand new Chop Shop designed Planetary Radio t-shirt that people can find in the Planetary Society store at

chopshopstore.com and a 200-point itelescopecope.net account astronomy account uh so that she can add it to her own telescope i believe she's got one but now she can do astronomy from anywhere around the world with that non-profit network of telescopes pretty much every place uh on this planet that you might want to have a telescope and remotely operate it. John Gallant in Lima, New York, who enters regularly, he said the next total solar eclipse over North America is what we mentioned. April 8th, 2024, goes right over his home in Rochester, New York. And this is why they call Carbondale, Illinois, the eclipse crossroads, because it is the one spot where the just-past Great American Eclipse will cross over, cross-pass with the 2024 Great Eclipse. I have one other, just because this

is so nice. Amelia Gabriel in Newport News, Virginia, she did get it right. She was not chosen by random.org, but she said, hi, my name is Amelia Gabriel, and I am 10 years old. I want to be an astrophysicist, and I listen to planetary radio with my grandma. You think we should send her a shirt? That's awesome. Yeah. All right. Amelia, you know, we're always reluctant to do this kind of thing,

because then, of course, we'll have every young astronomy and astrophysics enthusiast in the country asking us for coveted Planetary Radio t-shirts. But what the heck, you deserve one. So congratulations, Amelia. And we look forward to interviewing you on the show in about 20, not quite 20 years when you get your Ph.D. and you're out there making waves in astrophysics. Indeed. Move on to the next trivia contest. Totality for this eclipse was two, two and a half minutes, depending on where you were. But that varies depending on where the moon is in its elliptical orbit and where the sun is and earth and all that good stuff. So tell me, and where the sun is, and Earth, and all that good stuff.

So tell me, to within a minute, what is the longest possible time of totality for a total solar eclipse as seen from the surface of the Earth? Go to planetary.org slash contest. Wow, I can't wait to hear the answer to this one. This never occurred to me, and I have absolutely no idea. So get us your answers by, and the deadline for this one is also going to be the 30th, Wednesday, August 30th at 8 a.m. Pacific time. That's the deadline. Somebody out there is going

to be chosen by random.org, somebody with the right answer, and is going to get a 200-point itelescope.net account, a brand new Chop Shop designed planetary radio t-shirt, and, and, and, and a commemorative Carbondale, Illinois, Great American Eclipse shot glass. I picked up a few at a rather famous discount store while I was there. All right, everybody, go out there, look up in the night sky and think about how the right kind of darkness can bring light to your life. Thank you and good night. I have no clever comments about that. That was just a nice thing to wish for people and I join you in that. He's Bruce Batts, the Director of Science and Technology for the

Planetary Society, who joins us every week here for What's Up. Get some rest, Guy. We've earned it. You too. We'll celebrate the Cassini mission with a free live show at Caltech in Pasadena on Monday, September 18th. You can RSVP for free at scpr.org slash events. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its Never Eclipsed members. Daniel Gunners, our associate producer. Josh Doyle composed our theme, which was arranged and performed by Peter Schlosser.

I'm Matt Kaplan. Clear skies.