Planetary Radio: Space Exploration, Astronomy and Science - Cassini, Voyager and beyond with Linda Spilker

Episode Date: August 18, 2021

Cassini project scientist Linda Spilker is back to describe how data from the Saturn mission that ended four years ago is behind new, trailblazing science. Linda has also rejoined the team behind NASA'S Voyager mission that is celebrating important anniversaries. She closes with convincing arguments for missions to Saturn’s moon Enceladus and the ice giants Uranus and Neptune. Bruce Betts gets on the Cassini train with this week’s space trivia contest. Discover more at  https://www.planetary.org/planetary-radio/linda-spilker-cassini-voyager-outer-planetsSee omnystudio.com/listener for privacy information.

Another great conversation with Linda Spilker, 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. The Cassini Mission's project scientist is back with more news from a mission that officially ended nearly four years ago. Data gathered as the great orbiter flew through the plumes above Saturn's moon Enceladus has now been shown to be consistent with biological activity below the tiny world's icy exterior. Linda has also rejoined the Voyager team as Deputy Project Scientist, so some of her thoughts are in the space between the stars. There's much more in our latest conversation with Planetary Radio's most frequent guest.

Bruce Betts is also thinking about Cassini, and he'll ask you about the spacecraft in his new What's Up Space Trivia contest. We're all getting tired of living in the virtual world, aren't we? Fortunately, as we stay safe, there are a couple of great upcoming events that will let you set sail with LightSail 2 and join Earth's smartest Martians. First up at 1 p.m. Eastern, 1700 UTC, on Saturday, August 28th, is the premiere of Sailing the Light, the Planetary Society's beautiful new documentary about our light sail.

I hope you'll join Bill Nye, Bruce Betts, Jennifer Vaughn, and me right after the online screening for a conversation about the project. Check out the trailer at youtube.com slash planetary society, where you can also set a reminder. We'll head for the red planet next with our friends at Explore Mars. Their Humans to Mars Summit is free this year, but you'll need to register. I'll be co-hosting the stream and talking with a few of the outstanding guests and speakers. This one is September 13 through 15. You can learn more and register on the Explore Mars website. The link, along with many others, is on this week's episode page at

planetary.org slash radio. Scroll down a bit on that same page and you'll be able to sign up for my free monthly newsletter. The August edition has just been published. Great space headlines await you in the August 13 edition of the Downlink at planetary.org slash downlink, beginning with an explanation of why Perseverance came up empty-handed after its first attempt to collect a sample on Mars. The fault was in the crumbly rock, not the spacecraft. Two Venus flybys by separate spacecraft within 24 hours? Yes, it happened just as Bruce Betts said it would last week, on August 9th and 10th. The traffic jam included NASA and ESA's Solar Orbiter, followed by ESA and JAXA's BepiColombo mission to Mercury.

And NASA researchers have used data from the OSIRIS-REx mission to provide a nearly 300-year margin of safety regarding near-Earth object Bennu. The worst odds come in the year 2182, when there will be a 1 in 2,700 chance of a bump in the interplanetary night, so you can tell your great-great-great-great-grandchildren to breathe easy. Let's go directly to my conversation with Linda Spilker. We talked a few days ago. Linda, welcome back once again to the show. I have no idea how many times you have been my guest on Planetary Radio, but I do know I'm absolutely confident that you have been heard more than any other guest, probably

a record that's going to stand for a long time. So once again, welcome back. It's great to be back, Matt. Thank you very much. We've spent virtually all of these previous sessions talking about Cassini, for which you continue to serve as project scientist. We're going to go in a slightly different direction this time, although we'll, don't worry, we'll come back to Cassini, everybody, because it's going to be integral to some

of the things that we are going to be talking about. But as you pointed out to me when we were talking about this, pulling this together once again, it's a big month, August of 2021, for the Voyager mission, particularly Voyager 2, a mission that you spent 12 years on before moving to Cassini, and you are affiliated once again. Why is this a special time in the grand tour of the solar system? Well, I guess they finished the solar system. Now it's a grand tour of interstellar space. Well, this is a special month because 40 years ago on August 25th, Voyager 2 had its closest flyby of Saturn. And that's the same planet that Cassini circled for 13 years. So just

a nice overlapping in studying of this very interesting world. And so Voyager 2 was the second flyby of Saturn. And we learned a lot more about the Saturn system. And for Voyager 2, that was the time when the scan platform got stuck. And we were behind the planet right at closest approach. And so in the intervening years between Saturn and Uranus, we figured out how to get Voyager scan platform working again to take really fascinating data at both Uranus and at Neptune. And there's an anniversary to celebrate regarding that last big world in our solar system, right? That's right. On August 26th, we flew by Neptune. And so that's another anniversary. And that was in 1989.

So two big flyby anniversaries for Voyager in August. I think I was correct in saying that you are once again affiliated with the Voyager missions that you worked on so many years ago. Am I right? That's right, Matt. I'm now the Deputy Project Scientist on Voyager. I have the privilege and pleasure to work with Ed Stone, who has been the Project Scientist throughout the mission. And what a wonderful feeling. It's almost like coming home, coming back to this mission where I first launched my career at JPL and literally went to my first

launch watching Voyager start its journey, Voyager 2 in particular, into the solar system. And so it's really great to be back and to see just what Voyager is up to these days now that both spacecraft are in interstellar space. It turns out that Voyager 1 crossed the heliopause into interstellar space in 2012, and Voyager 2 followed in 2018. I think it's absolutely charming that now, 44 years after you got to JPL, just in time for the launch of the spacecraft, that you are back in your old job, right? Deputy Project Scientist. And working with Ed Stone, one of the great planetary scientists and human beings that

we have, one of the greatest, I should say, that we've had the honor of hosting on Planetary Radio. We need to bring him back again pretty soon as well. I can certainly see how this would be very satisfying for you. Oh, it is, Matt. I wasn't deputy project scientist when I first started. I was just fresh out of college. I actually started working with one of the instrument teams.

The infrared instrument team, IRIS, was the infrared radiometer team, and then came back as deputy project scientist. And what's interesting is that Voyager team went on to propose a Cassini infrared instrument as well. That was the composite infrared spectrometer. And I had enough years under my belt and education at that time that I actually was a co-investigator with the composite infrared spectrometer team. So I have a tie to Voyager through the infrared instrument as well. You know, that would have been impressive if you had gone directly from college to a deputy project scientist on the grand tour of the solar system. Sure would have, yes.

or the solar system. Sure would have, yes. So let's talk about what Voyager is up to now, because you also pointed me to a pretty significant piece of research that has surfaced recently because Voyager, both Voyager spacecraft, which we hope we're going to continue to be in touch with for a long time, right, are still doing great science. That's right, Matt. Both of them are still operating, but each year with a little bit less power, we're having to be more

and more careful starting to turn off certain heaters on the spacecraft and on the instruments to keep both Voyagers going. And if you think about it, the two Voyager spacecraft is the first time we've had in-situ studies, studying the local environment around the spacecraft in what we call the very local interstellar medium. And so now they're outside the heliopause, we're studying the interactions going on, the plasma density, that very fine mist of ions and electrons that's an interstellar space called the plasma, and what the effects of the sun still have out in the very local interstellar space called the plasma and how what the effects of the sun still have out in the very local interstellar medium it turns out that the solar wind sometimes

there are shocks from the sun within the solar wind that actually go through the heliopause and we can see these shocks in the interstellar medium and by at those, we can actually get the density of that plasma around Voyager. So the heliopause is now we know apparently not really the end of the sun's influence over the space that surrounds us. That's right, Matt. It turns out that that influence continues on. And we'd like to see for just how far that influence continues. And we'd like to see for just how far that influence continues. Right now, Voyager 1 is 150 AU from the sun, a little bit more than that. And Voyager 2, not far behind, is about 130 AU from the sun.

And to put that in perspective, the outer edge of the Kuiper Belt is at about 50 AU. So Voyager has gone all the way across the Kuiper Belt on out into interstellar space. And yet interstellar space, that's huge, the distance between the stars. Still got a ways to go before it gets out there beyond the Oort cloud, right? That's right. Yeah. You're talking light years, light years over at the edge of that. You know, I just remembered something, another charming fact that was brought up by Alan Stern, principal investigator for the New Horizons mission, of course, who talked on this show a couple of weeks ago about how they pointed New Horizons and took an image looking out from where New Horizons is now, considerably behind where Voyager is,

the two Voyager spacecraft, looking toward the section of space where I think it's where Voyager is, the two Voyager spacecraft, looking toward the section of space where I think it's where Voyager 1 is. Of course, it was far too small to see, but I still thought that was a fairly romantic notion. Did you hear about that? No, I didn't hear about that, Matt. What a nice tribute. In fact, Voyager uses information from New Horizons to give us a warning of some of these shocks coming out from the sun. New Horizons, being closer to the sun, would see them first. And that gives us a few years notice that something might be coming our way. And so it's nice to have no idea that New Horizons was sort of acting as an early warning satellite for the Voyager spacecraft.

That's right, Matt. It does. There is some other work that has been done just recently where, and I wasn't aware of any of this, so I hope you'll take us a little bit farther into talking about this interstellar medium, the plasma that you already mentioned. I got the idea from what you sent me in the abstract I read that to detect the changes in this plasma, they had to wait for these sort of shock waves to come out from the sun. But now someone has come up with a better technique. Yes, Matt. It turns out that on Voyager 1, the plasma wave spectrometer, Yes, Matt, it turns out that on Voyager 1, the plasma wave spectrometer, basically it's two antennas pointing out that measure the radio waves that are generated from the oscillations in the plasma.

It turns out that it's taking data all the time. Voyager 1 and Voyager 2 each have this plasma wave spectrometer or PWS. But on Voyager 1, we're still able to take high-rate data with PWS, and that's the key. And that story in and of itself is fascinating. It turns out that the PI of PWS, Don Garnett, when he put his instrument on board Voyager, he really wanted to get some what he called high-rate data. And so they figured out a way where he could actually, in between, where we would take an image with Voyager, we'd take 48 seconds to read that image in, and then there'd be a 48-second pause to refresh the camera. And in that 48-second pause, it would be difficult to downlink the data. Those would sort of be zeros coming back. And so Don Gurnett for PWS said, how about if I just stick my data in just like an imaging frame writing it

its bits just like lines of an image and now you'll have a continuous rate to play back the data from the two voyagers off the tape recorder we have a digital tape recorder on voyager that holds a hundred pictures and so throughout the voyager, the flybys of the planets, we got lots of this high rate PWS data. And now three times a week, we actually put high rate frames, 48 seconds long onto the tape recorder, still working on Voyager 1. And then every few months we play back the tape recorder. We have to array the 70 meter and three 34 meter stations at the dsn to get back the signal coming back now from the tape recorder on voyager one and it turns out you get spectrograms basically information with frequency and if you

add the 48 second frame together and put all of those side by side over several months, then you can start to look for patterns. Are there places where there's a frequency that stands out? And sure enough, with very careful analysis of these data, and that's in a new paper by Stella Oker, you can actually start to see this very, very faint plasma signature these these sort of the oscillations in the plasma itself and you don't need the shocks anymore but can continuously measure the plasma density in these very faint very faint little signals and so what an interesting story that we can now see this nearly continuously as long as the Voyager tape recorder keeps working and as long as we can

download those data. And a PWS is healthy and doing quite well. It's a very low power instrument, and it might be one of the very last instruments that we turn off on Voyager, potentially lasting out into the late 2020s, maybe even to 2030. Just amazing. So many other things come to mind. As you mentioned this, I mean, one, nature abhors a vacuum because even out there between the stars,

there's still some material for us to measure, some energy as well. But also, we're not just using tape recorder here as a euphemism, taping the data. We're talking about a mechanical tape recorder, right? That is still two of them that are still functioning after now, close enough to half a century. Well, it turns out just the Voyager 1 tape recorder is still being used. We aren't using the tape recorder on Voyager 2 at this point. So just on Voyager 1, but Voyager 1 is, you know, the furthest from the sun. And

now measuring this, I think of it as a background hum from the plasma that's out there in interstellar space and from the energy that it contains. And it's just so exciting to think that we can do this with Voyager. We're still measuring the magnetic field direction and the strength of the magnetic field, measuring the composition, not only of the electrons, but the ions, which could be atoms or molecules that make up this plasma. Plasma is really very fascinating. It's one of the most abundant forms of matter, ordinary matter in the universe. You figure you have four phases, gas, liquid, solid, and then plasma. And the plasma is associated with the stars. It fills the space in between the planets in our solar system and

goes on into interstellar space, filling the space between the stars. It's very rarefied. And it's charged, which means it can be influenced by the magnetic field. It's charged, which means it can be influenced by the magnetic field. High energy and high temperature generally, high enough to have taken an electron or two off of an atom or molecule to create then that plasma. Let's pull it back into the solar system a bit. As you said, we're also celebrating that flyby of Neptune by Voyager 2. celebrating that flyby of Neptune by Voyager 2. Still no missions planned to those twins out there,

those ice giants, Uranus and Neptune. I'm sure you were following when the most recent interplanetary or planetary science missions were announced by NASA. We got two spacecraft now being planned for a visit to Venus, and we had both of those principal investigators on the show recently. Nothing against them, of course, but you are still one of those who very much wants to see a mission headed in the other direction, aren't you? Oh, absolutely. After having seen the Uranus and Neptune data returned by Voyager, it only seems natural at some point to visit one or perhaps both of these worlds to go back with a mission like Cassini, an orbiter, perhaps with probes for the atmosphere or maybe a probe to study Triton in more detail, Neptune's moon Triton, but definitely to go back and to understand these ice giants and be able to compare them then to Jupiter and Saturn. The moons, the quick glimpses we got of the moons around these planets were fascinating, especially the large moon Triton at Neptune. And to go back and understand not only the moons, but the ring systems that each world has and the planets themselves,

because each one is so different Neptune is releasing more energy than it receives from the sun Uranus is not Uranus is tipped on its side looking like a giant bullseye with its rings sometimes pointed toward the sun and that was the configuration at the time of the Voyager flyby. So to go back would be so exciting and so interesting. We're in the midst of something called the Decadal Survey. And one of the outcomes or outputs of the Decadal Survey will be, what should our next flagship missions be? And we have Europa Clipper in its stage instruments being built, the spacecraft put together. So after Europa Clipper, what's the next big planetary flagship mission? And I'm hoping it could be a mission to one of the ice giants, either Uranus or Neptune.

I have a slight preference for Neptune just because Neptune has this fascinating moon Triton with geysers that we saw with Voyager on its surface. with geysers that we saw with Voyager on its surface, and some hints that perhaps maybe Triton might have a subsurface liquid water ocean, very similar to Saturn's moon Enceladus and Jupiter's moon Europa. There's another reason that has come up many times on the show, probably with you and others as well, and that is that as we look out across the galaxy and find other worlds, thousands of them now, so many of them look like either twins or brothers, sisters of Uranus and Neptune. And so it would seem that this is an opportunity for us to learn more about planets all over the place.

Yes, I think that would be a great opportunity. And hopefully in the next decade, we'll take advantage of it. We're going to come back to this consideration of the next big mission from NASA, so-called flagship mission. But before we leave this, I want to give more evidence of how deeply you're involved in working with the outer planets because you co-chair something called the OPAG. Tell us about that. OPAG is the Outer Planets because you co-chair something called OPAG. Tell us about that. OPAG is the Outer Planets Assessment Group. We get the Outer Planets community together twice per year, hold meetings and discuss and get updates from currently flying missions, updates about ideas or proposed missions. And then we put together a white paper for the decadal survey

with OPEC's priorities and we really think that an ice giant mission should be a top flagship mission priority followed maybe five years or so later with a mission to an ocean world like Enceladus or perhaps Europa to try and have a mission that could make measurements perhaps in Enceladus's case you could fly through the plumes or directly sample the plumes, maybe land on the surface and get directly from these products coming from the ocean what the ocean might be like. With Europa, perhaps there are events on Europa as well.

And perhaps take a Europa lander to land on the surface of Europa and make similar measurements. And the key there is to figure out, do these ocean worlds potentially harbor life? There are some indications from Enceladus, from Cassini flying seven times through and directly sampling the gas and the particles coming from the plume that we have. We have organics, we have evidence for hydrogen and methane and salts and some of the key ingredients for life. Some of the discoveries by Cassini led us to know that Enceladus has a global liquid water ocean beneath its icy crust. There are five tiger stripe fractures is what we nicknamed them at the South Pole.

And over 100 individual jets of material are shooting out into space, carrying not only water vapor and water particles, but all of these other very interesting key ingredients. Some of those, the excess of hydrogen, we saw methane, also some salts that could only form at very high temperatures, perhaps deep on the seafloor of Enceladus, point to potentially hydrothermal vents. And these hydrothermal vents would be a source of energy that could be used by any form of life that could be potentially on the seafloor. We know deep in the Earth's oceans where sunlight doesn't penetrate, we find around Earth's hydrothermal vents,

teeming with little islands of life provided with the nutrients and the energy to thrive in an environment very deep in the ocean. So we wonder, could something similar be happening on Enceladus or perhaps other ocean worlds? And so it's just very intriguing to think about a mission to go back. A lot of modeling and a lot of studies are being done. We're still going through the Cassini data and doing lab work and trying to see how you could create some of the spectra that we saw both in the particle and in the gas data. Looking for evidence when we go back for long-chain hydrocarbons, that could perhaps point to life.

More of my conversation with Linda Spilker is coming up right after a short message. Hi again, everyone. It's Bruce. Many of you know that I'm the program manager for the Planetary Society's LightSail program. LightSail 2 made history with its launch and deployment in 2019, and it's still sailing. It will soon be featured in the Smithsonian's new Futures exhibition. Your support made this happen. LightSail still has much to teach us. Will you help us sail on into our extended mission?

Your gift will sustain daily operations and help us inform future solar sailing missions like NASA's NEA Scout. When you give today, your contribution will be matched up to $25,000 by a generous society member. Plus, when you give $100 or more, we will send you the official LightSail 2 extended mission patch to wear with pride. Make your contribution to science and history at planetary.org slash S-A-I-L-O-N. That's planetary.org slash sail on. Thanks. There are a couple of articles along these lines. One that you pointed me to, and another one that I showed to you. First, the one that you came up with, and this is by,

I guess it's led, I guess, by Morgan Cable, a paper called The Science Case for a Return to Enceladus. And you recommended talking to Morgan on some future Planetary Radio episode. We'll put up links to at least the abstracts for all of these things we talk about on this week's show page at planetary.org slash radio. I assume that this is a paper that you've read and Morgan and her colleagues make a good case. Right. Yes, I'm actually a co-author on the paper by Morgan Cable.

You know, I didn't see your name. I was surprised when I didn't see it. I guess I missed it. Sorry, Linda. I'm not surprised at all. That's okay. There's just a very long list of co-authors. Lots of people very interested in this topic. And it just goes on to describe and make the case for a potential life on Enceladus

by looking at the fact you have the liquid water, you have the energy source potentially from the hydrothermal vents, as well as a whole host of organics and salts and other key ingredients that provide an environment in which life might thrive. And with Enceladus, what's nice is you have direct access to fresh material coming from the ocean itself through these jets that are spewing out into space. And so with all of these conditions being right, we really wonder, could you perhaps have life on Enceladus? And the second paper you pointed me to talks about a process called methanogenesis, where you could have biotic production of methane. And that could explain the escape rates of methane and hydrogen that we saw in the Cassini data. And you have methanogenic colonies of life around the alkaline hydrothermal vents that are present on Earth's seafloor. And so we wonder if you could have a similar kind of process going on

in Enceladus. And as I said, a lot of lab work is going on, a lot of looking at Earth analogies with Earth's hydrothermal vents, and basically getting ready for the next kinds of instruments that we'd want to send on a mission that would go back to Enceladus. And there's just a lot of work going on in this area for what kinds of instruments would you send to look for long-chain hydrocarbons and what would be the best way to make those samples. Even down to perhaps maybe one way is to go perhaps collect a sample of the ocean someday and maybe even bring it back to Earth where we could do all kinds of experiments here on Earth as well. And that might be the

flagship after the next flagship kind of mission. But there's always that possibility to bring back a sample from one of the oceans of these worlds. That paper about methanogenesis, I hope I got that right. There is an article written by my colleague at the Planetary Society, Jutan Mehta. It's a July 28th article at planetary.org that goes into this a little bit and talks about how they modeled this fascinating work that was done by these researchers. They set out a 50,000 simulated environment runs, because they basically built a model and then, you know, put different variables into it. About a third of those would have been habitable for the kinds of earth creatures you just mentioned, those critters that live down around hydrothermal vents here on the home world.

Yes, it's fascinating. It's now starting to make these models and actually do statistical runs where you can look at if you produce conditions that are very similar and tweak them a little bit and make all of these runs, what do the statistics start to look like? The data behind this paper provides proof once again of something that we have talked about, you and I, many times, that Cassini is the gift that keeps on giving because this was based on that data that Cassini gathered largely when it flew through those plumes. You're still the project scientist for the mission. It has to be rewarding to see this kind of work going on. Oh, it is, Matt, absolutely, to see it continue. And September 15th is going to be the four-year anniversary of the Cassini end of mission.

It's just amazing how quickly that time flies. And it's very likely that over the next several decades, we'll continue to look at the Cassini data, build models to best match those data, and continue to try to understand that very interesting, tiny little world, only 500 kilometers in diameter, so small, and yet so very interesting. What a night and what a morning that was for end of mission. And then, you know, we followed it with that standing room only crowd at Caltech, which we'll put up a link to that show. Well, those several shows, actually, because there were shows that we based on the work we did during the actual end of mission and then the celebration of the Cassini mission that you were part of it at Caltech. So great, great memories. And it sure doesn't seem like four years ago.

No, it doesn't. It's amazing how fast that time has gone by. And how. As we get close to maybe the end of this conversation, I just wonder, I mean, you have so much still going on at JPL, this return to the Voyager mission. You're a JPL fellow. You recently got the title Senior Research Scientist. So congratulations on that, because that's up there in the science stratosphere at JPL and really any place. You've been at this for a very long time. Is it just as fascinating

as ever for you? Yes, Matt, it really is. Because it's like just around the next corner, who knows what we might find. And that's so true now, especially with Voyager, with the Bose spacecraft out in the interstellar medium, and making new discoveries in the Voyager data to this day. And I know when I first started on Cassini, I would go back and look at Voyager data from Saturn and use that to build the kinds of signal to noise or whatever I was looking for in the Cassini data. So I'm sure with Voyager and with Cassini, that will continue on for years to come. And it's just wonderful to be back on Voyager. What's fascinating is that Voyager's power is degrading by about four watts per year. That means we're having to start to very carefully consider what to turn off.

One of the first things that they did with Voyager is to turn off the heaters to some of the instruments. Here, the temperatures would drop 40 or 50 degrees centigrade and yet the instruments continued to work. And so we've now turned off several heaters on the cosmic ray spectrometer and the low energy charge particle instrument. The instruments keep working. The little stepping motor on LECP keeps stepping and just a little bit of recalibration and they continue to return good data. And they're so far outside their engineering specs and yet a spacecraft that was so well built and crafted that we can continue to get data even with those instrument heaters off that the power from running the instrument is just enough to keep everything working on the Voyager spacecraft.

So what an incredible mission. We really know how to build hardware at that place where you work. And when you consider that it's sending that signal across all those many, many, many kilometers or miles, it's all the more amazing. Here's the other thing that I meant to ask you earlier. It's all the more amazing. Here's the other thing that I meant to ask you earlier. As we look forward to the launch and arrival at Titan of Dragonfly, I'm sureometers that can find those long polymers, those long hydrocarbons that, you know, you would like to look for at Enceladus. Does seeing that mission, Dragonfly, also make you feel good about heading somewhere else like Enceladus?

Oh, absolutely. Dragonfly is an incredible mission. And the chance to go back to titan and you're right building instruments because they're going to collect samples out of the front two legs of dragonfly and then perform experiments on those samples with a very sophisticated spectrometer and perhaps we could fly some of those instruments to another ocean world the major difference is titan has an atmosphere so they're having to design the instruments to another ocean world. The major difference is Titan has an atmosphere, so they're having to design the instruments to work with an atmosphere, whereas many of these other ocean worlds, especially on the surface, you wouldn't have an atmosphere.

So there are some differences. But what a great mission to think about actually flying this huge octocopter across the surface of Titan and, you know, scouting out landing sites and then coming back and then flying to the next landing site and continuing the scouting and exploration. An absolutely incredible mission. And that mission, of course, led by the Johns Hopkins University Applied Physics Lab.

Do you ever get across the hall or to another building and talk to your colleagues who even sooner than Dragonfly are hoping to send Europa Clipper off to that moon of Jupiter? Well, it's a little hard to walk across the hall at this point though, Matt. That's true. There are all kinds of telecons and other ways in which we keep in touch. A virtual walk across the hall. A virtual walk across the hall. A virtual walk across the hall. I mean, even our OPEC meetings are virtual at this point. But I am looking forward to the time when we do get back together,

both at OPEC meetings and planetary science conferences, and to see my colleagues. They're slowly starting to open up JPL on a voluntary basis if you want to go back a day or two. And I'm sure there'll be more plans to continue to open up in the future. Linda, it has never been less than wonderful to talk with you on Planetary Radio. I'm so glad we had the chance to do this again. And with your permission, we'll do it yet again sometime in the near future. Oh, absolutely, Matt.

It's always wonderful to talk with you and chat about all these interesting topics that come along the way, whether it's Voyager or Cassini. Linda Spilker of JPL is the project scientist for the Cassini mission, the deputy project scientist for the Voyager mission that has now been underway for 44 years, and co-chair of NASA's Outer Planets Assessment Group. Time for What's Up on Planetary Radio. Here is the chief scientist of the Planetary Society, who joins us every week at about this point in the show. It's Bruce Batts. Welcome back. Come on. I need a little more enthusiasm than that. Hi, Matt. I'm really excited about doing Planetary Radio this week. We got some cool stuff.

Well, there's always cool stuff. Prove it to me. All right. How about you look in the west in the early evening and see super bright Venus? And if that's not good enough for you, look over in the other part of the sky, over in that east direction, and you'll see a really bright Jupiter and above it to its right, yellowish Saturn. But wait, don't order yet. I can also offer you the moon hanging out near Saturn on August 20th and near Jupiter on August 21st. Is this a package deal? It is. It's a package deal. You get all the planets for one low price of awesomeness.

All right, we move on, though. We move on to this week in space history. It was 55 years ago this week in the fine year of 1966. Lunar orbiter took the first image of Earth from hanging out around the moon. You know, this came up when we talked with Andy Chaikin because we talked about the Earthrise image that everybody knows so much better from Apollo 8 and how, yeah, the lunar orbiter had already done it, but it meant so much more to know that a human was actually seeing that site and capturing it

with his Nikon or whatever, Hasselblad, whatever they gave those guys. That's a prettier, nice color picture too. 1976, 45 years ago, Luna 24 returned samples from the moon. A robotic sample collection, last of the three flown by the Soviets. Yeah, and the last of, until China did it. What, last year or was it early this year? I forget.

But anyway, we're back in the business of sample return, we Earthlings. Yeah. All right, we move on to Random Space Fact. That was lovely. Thank you. Uranus's moon, Miranda. It's a weird looking thing, but listen to this. It's got big old canyons from massive faulting that

are as much as 12 times deeper than the Grand Canyon. But wait, once again, don't order yet. Here's the amazing, amazing fact. Miranda's low gravity and huge, large cliffs, if you dropped, as you would do, Matt, if you dropped a rock off the edge of the highest cliff, it would take about 10 minutes to reach the foot of the cliff. I would do that. But a rock? That's so boring. I would drop a piece of pie, a piece of cherry pie. A bowling ball.

I'd use a bowling ball. Yeah, why not? Bowling ball and cherry pie. We can do the classic Galileo, Dave Scott on the moon experiment, but instead of a hammer and a feather, we'll use a bowling ball and cherry pie off Miranda's cliffs. What a plan. Party on. You beat me to mentioning the feather. I really wanted to get that in. Well, you edit the show. I mean, you can still do it. That's true. I could change everything. I'm in, I have the power. Shall we move on to the trivia contest,

oh powerful one? Yeah, it's entirely up to you and the editor. All right, so I asked you to name all the Olympics for which an Olympic torch was flown in space. How'd we do, Matt? Dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun,

dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, dun, Sorry, I didn't know we were really going to keep going through the whole thing. Yeah, sorry. I didn't need it, actually. That's the best part. It's really fascinating. A lot of listeners found this fascinating. I'm going to let David Mustardi of California provide the beginning of the answer with a little Olympic haiku.

One small step for torch, Atlanta, Sydney, Sochi, Giant Leap for Sport. Nice. And I believe he's correct, but let me read the winner to you as well and then see if you confirm it. I am very pleased to say that Random.org chose Claude Plymate. Claude, who is a past guest on this show, he and his lovely wife recently retired from the Big Bear Solar Observatory, where we did an interesting planetary radio episode a while back. Claude is also a regular listener to the show.

He last won, he is a previous winner, won once before three years ago, almost exactly three years ago. Random.org has quite a sense of timing. He said they were the Games of the 26th Olympiad. That was Atlanta, 1996, Space Shuttle Columbia, STS-78. The Games of the 27th Olympiad, a.k.a. Sydney, 2000, Atlanta Space Shuttle, STS-101. And the 22nd Olympic Winter Games in Sochi, 2014, on Soyuz TMA-11M.

Does that match what you discovered? It did. And the last one went and hung out on the International Space Station. Yeah. And I read also went on an EVA. At least we heard that from many, many listeners. It actually brought the torch outside. It probably didn't stay lit. Actually, that was also addressed by a number of people that we'll get to here. Congratulations, Claude.

And so we are going to be sending you that fabulous Planetary Society kick asteroid, rubber asteroid. We did get some nice poems from our poet laureate and elsewhere, but I'm afraid they're a little bit too long for us to read. But there's just some other priceless stuff here, like what we got from Vlad Bogdanov in British Columbia, the idea of sending an Olympic torch to space was initially conceived by Australian-born NASA astronaut Dr. Andrew S.W. Thomas. in Athens was broadcast via satellite to Ottawa, where it was relit by laser beam for the Montreal Games. Interesting, weird, and doesn't count. No, definitely not. And I think he knew that too. Ben Drought in Iowa discovered that there was hope that the torch would be lit in a special container in 1996, but NASA didn't go for that. A little bit of mythology from Mark Little in Northern Ireland. Back in the day, of course, Zeus stole fire from us mere mortals. The Olympic torch represents Prometheus stealing it back from Zeus and returning it to humanity. We all know what Prometheus got as a reward for that from

Zeus. If he hadn't stolen it, we wouldn't have been able to ignite the rockets that take us into orbit and beyond in modern times. So we owe our endeavors in outer space to an act of theft. Wow, nice job, Prometheus. Finally, this from Pierre-Louis Phan in France. Hopefully, one day the Olympic torch will be carried to Olympus Mons on Mars. Cool. There would be some amazing, amazing Olympic sports you could do there. And it will be cool because, of course, there won't be enough oxygen in the atmosphere. At least not until after the terraforming is complete to light the torch on Mars.

So don't hold your breath, anyone. Oh, gosh, let's move on. So here's a new question for you. You've been hearing all about Cassini. Well, not all about it. It's a very complex mission. Tell me how many orbits of Saturn did the Cassini spacecraft complete? Go to planetary.org slash radio contest.

Would you accept a bunch? From you, yes. From anyone else, no. Well, there's some guidelines for you. At least we've given you a hint. You have. Have we? No.

We have until, you have until August 25th. That's Wednesday, August 25th at 8 a.m. Pacific time. And get a load of this prize. Our friend Thomas Romer, the guy behind chopshopstore.com, where you will find all of the Planetary Society merch and a whole bunch of other good stuff, including the Planetary Radio t-shirt, of course. He has a third round of his robotic spacecraft poster series underway. There's a Kickstarter for it that you can get in on at bit.ly slash spacecraft3.

That's, you know, bit.ly slash spacecraft3. If you win this one, then you in a couple of weeks will have your pick of any poster, any of the existing posters from the first two rounds, or the three new ones, which we can announce will be Pioneer, Juno, and Viking. Now those won't be ready until October, roughly. You can also pick one from inventory. Those are a pretty good selection, too. Voyager, Mars Science, because he's kind of lumped together now, Curiosity, Perseverance, and Ingenuity.

Sputnik, Mars Exploration Rovers, Opportunity and Spirit, New Horizons, Rosetta with Philae, and Galileo. Get those entries in, and you might just win yourself a very cool poster. They're beautiful. All right, everybody. Go out there. Look out at the night sky and think about falling bowling balls

and pie. Thank you and good night. Cherry pie. That's the absolute favorite of everyone on Miranda. I'm sure you know why. He knows why. He's Bruce Betts,

the chief scientist of the Planetary Society, who joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its members who span the solar system and beyond. Join the grand tour at planetary.org slash join. Mark Hilverda and Jason Davis are our associate producers. Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. Ad Astra.