The Next 10 Years: Continuing our Solar System Tour

Mat Kaplan: [00:00:00] What will the next 10 years bring the rest of our solar system? That's this week on Planetary Radio. Welcome. I'm Mat Kaplan of the Planetary Society, with more of the human adventure across our solar system and beyond. Last week we took up Mercury, Venus, and Earth's moon. Now our look ahead takes us to Mars. The giant outer planets, and to the smaller bodies that pepper our entire solar system and beyond.

Three more great scientists will talk about their contributions to the equinox edition of The Planetary Report, focusing on what we've already learned and the big questions that remain in each of these realms. Then we'll check in with Bruce Betts for what I think is a particularly entertaining edition of What's Up, including a new space trivia contest.

Headlines from the down link are moments away. First though, here's an opportunity I'm excited about. Our good friends [00:01:00] at Explore Mars, creators of the annual Humans to Mars summit have asked me to moderate an online discussion with NASA Chief Scientist Jim Green, and Penny Boston of the NASA Astrobiology Institute. Many of you will hear this too late to join the live event at 1:00 PM eastern on April 1, but Explore Mars will make the complete conversation available on demand.

The next Planetary Science Decadal survey, that community authored document that will guide NASA science priorities from 2023 through 2032 will place an increased emphasis on astrobiology and planetary defense. The Planetary Society supports the inclusion of these topics. It was anticipation of this next survey that inspired the interviews you heard here last week and are about to hear this week.

In person work on most NASA projects, including the James Webb space telescope, the Orion spaceship, and the space launch [00:02:00] system has stopped due to COVID-19 restrictions. One exception is NASA's Perseverance Mars rover which must blast off during a narrow July, August window while Earth and Mars are optimally aligned. If Perseverance misses that window, the next opportunity will be in 2022, along with the already delayed Rosalind Franklin rover from the European Space Agency.

Also, still in progress despite COVID-19 quarantines, NASA's Commercial Crew program, which is preparing for its inaugural astronaut launch in May. Those preparations hit a snag after a Falcon 9 rocket lost an engine during its fourth re-flight. A few days later, some Space X parachute testing hardware crashed to the ground during a helicopter drop test. Though apparently the parachute system was not at fault. It's unclear whether either incident will impact the May launch.

All of the fun and informative features of this week's down link are [00:03:00] online at planetary.org/downlink, or you can be like me and have it delivered to your inbox each week for free. We continue our steady progress from Mercury to the outer reaches of the solar system with a stop at the red planet. Ramses Ramirez is a planetary scientist and astrobiologist from the Earth-Life Science Institute. Part of the Tokyo Institute of Technology. He's also an affiliate scientist with the Space Science Institute. He joined me the other day from Tokyo. Ramses, welcome to Planetary Radio. I'm happy to have you kick off the second set, numbers four, five, and six of these conversations. With all of you six scientists who wrote articles for the current issue of the Planetary Report, and of course you took on Mars. Thanks for doing this and thanks for the article too.

Ramses Ramirez: Thank you and I'm very glad to be here Mat.

Mat Kaplan: Well, it's obviously a subject you care a lot about. We found the water up there on Mars. We [00:04:00] know more or less now where the atmosphere went. Kudos to the Maven Orbiter. We even found organics. What's left on the red planet for us to discover?

Ramses Ramirez: Oh, there is, there's really a lot to discover on the red planet. We're just barely scratched the tip of the iceberg. Like you've said, Maven has brought in a lot of good information about accessing the atmosphere escape rates today. On Mars, as we understand them, based on solar activity, and then they've been able to come up with estimates as to how much atmosphere Mars could have lost over time.

My main focus, my main specialty is really understanding the, the early climate of Mars because then you know, that has potential parallels to how life could have started on Earth. We see interesting geologic features on Mars. Lots of fluvial valleys and networks and uh, kind of like you can think of them as Grand Canyon-like features that required a lot of water, so there's a lot of evidence that Mars used to be a [00:05:00] more Earth-like planet in the past, with a thicker atmosphere.

What Maven was able to tell us was, or infer is how much atmosphere Mars could have lost from then and now, which was a pretty big number. At least half a bar or so, which would suggest that Mars had a thicker atmosphere that potentially could have supported uh, liquid water on the surface at one point, and who knows? Maybe could have fostered conditions that were suitable for the emergence of life there too.

Mat Kaplan: So, one bar, that's the pressure of our own atmosphere here on Earth, right? At sea level. So if Mars once had that much air, it's lost half of it?

Ramses Ramirez: Yeah, that's actually, that's the, the interesting thing is that those estimates are really only a lower bound estimate.

Mat Kaplan: Wow.

Ramses Ramirez: Because they're able to, what Maven was able to do was infer some escape mechanisms. We call them non-thermal escape mechanisms. But they were very [00:06:00] strong thermal escape mechanisms, other escape mechanisms that would have been present in the past that you know, is not easy to tease out of the Maven analysis that could have to lead to even higher escape rates. So then the inference is that perhaps the atmosphere was at least one bar or more in the past. So, yeah. It's very exciting.

Mat Kaplan: Well, Mars, since you are interested in its early history when it apparently did have a lot more air. Obviously it would have been more habital back then, at least to life as we know it. Put that in quotes, and its habitability that you obviously care a great deal about. I mean, your website, habitalplanets.wordpress.com. We'll put up that link on this week's show page as well. You had a term there that I'm not familiar with and maybe you could take a moment to explain it; "dynamic habitability."

Ramses Ramirez: Yeah, this is a new term based on some [00:07:00] astrobiology reports that scientists put together the past year or two uh, to the scientific community. They've used that word and I kind of like it because it describes very well what I'm interested in as far as the scientific research goes. What that really just means is that habitability is extremely complicated, in a nutshell. And the long answer to that is that it requires an interdisciplinary approach to be able to assess the habitability of planets. You cannot just look at say the solar factors or geologic factors or the atmospheric factors.

Planetary habitability or dynamic habitability is really a systems level analysis that requires the influx of many different disciplines interacting with each other to try to answer these very tough questions. You can't just rely on biology or chemistry, or any one discipline by itself. With the influx in data that we're getting from all these missions, the Mars missions and now the Mars [00:08:00] 2020, hopefully that will give us a lot more. Should give us a lot more information and these exoplanet missions, all these different pieces from all these different fields, plus biology and chemistry will be able to ... I think we're, we're on the verge of a renaissance or renaissance of knowledge.

Mat Kaplan: Sounds like planetary science which is by definition multi-disciplinary.

Ramses Ramirez: That's right.

Mat Kaplan: All right. Let's pick up the three questions that you chose for Mars. The big question's remaining. Just as your colleagues who also wrote for this issue of the Planetary Report did. The first of these takes us back to the atmosphere. What was the atmosphere composition? Not just how thick it was or how dense it was of a warmer, early Mars. You talked about this consideration that perhaps it may have been carbon dioxide like a lot of it is now, but also hydrogen? Co2 and hydrogen?

Ramses Ramirez: Yeah, this is an interesting idea that's [00:09:00] actually not too old. Several years ago, 2013, '14, around that time frame we had proposed this as a possible mechanism because really the story has been for you know, a long time that the climate models really predict that Co2 by itself and water vapor would not be enough to warm the planet, no matter what model. No matter how much CO2 you put in the atmosphere, the Co2 has a strong greenhouse effect, but once you get to high pressures it also likes to condense out of the atmosphere and reflect a lot of radiation out into space. So, there's kind of a sweet spot beyond which you can't maximize the warming from that and that warming was always well below the freezing point of water. So then that caused many investigators to look at other possibilities, so Co2 in addition to other greenhouse gases, maybe you know, SO2, methane, other [00:10:00] possibilities, and a lot of these have issues.

SO2 for instance is good for warming cold planets, but not good for sustaining warmth on warm planets because it pulverizes and becomes very refractive and once it gets warm, you start to rain, it actually rains out of the atmosphere. Methane also has issues with stability. The atmosphere and other things. Hydrogen, we proposed that to be the other gas next to Co2 that would have been put on early Mars, primarily based on meteoritic evidence suggesting that Mars used to probably out gas a lot of this stuff. A lot of volcanism on Mars probably, uh, on early Mars, could have been hydrogen rich based on the meteoritic evidence suggesting that the mantle, the deeper interior of the Earth could have been oxygen poor, more hydrogen rich, so from there we infer that the early [00:11:00] atmosphere on Mars could have likely also been hydrogen rich.

And it just turns out because of the radiant transfer details that the combination of Co2 and hydrogen really gives you a good bang for the buck. Co2 absorbs well at certain wavelengths. Absorption works at different wavelengths across the spectrum, but hydrogen then also absorbs well, or the combination of Co2, hydrogen absorbs well in regions where Co2 and water alone do not absorb well, so it kind of picks up these windows. Hydrogen itself is not really a good greenhouse gas, but if you put it in collisions with another big background gas like Co2, it'll, you'll be able to excite these transitions and have that combined molecular pair, Co2 and hydrogen to absorb very strongly, so that's what's going on there.

Mat Kaplan: An intriguing model, but how will we go about determining if this was [00:12:00] actually the nature of the martian atmosphere a billion or so years ago or more?

Ramses Ramirez: Yeah, this is a very good question and it's something that we will have to actually, I think, with the Mars 2020, maybe we'll get some answers. One thing you want to answer before you even answer the atmosphere composition is whether early Mars was warm or cold, so there's still that lingering debate.

Mat Kaplan: Yeah. That's your second question that you posed, uh, which has come up on the show before. Was it warm and wet or cold and icy and just got warm every now and then? But not for very long.

Ramses Ramirez: Exactly, and essentially what Mars 2020 can do and future Mars missions is start assessing. The rover's going to start assessing these terrains and look for evidence of icy features. So far, rover missions we have at [Gale 00:12:54] and the orbital missions have not found any convincing evidence of an icy early Mars, which gives [00:13:00] more weight to the idea that Mars was probably not that icy. It was a pretty warm planet in the past. We need to continue those analysis and to verify that, but that seems to be again, more promising, this idea that Mars was once a warmer and wetter planet. But given that, if we're able to show that, in conjunction with that, yes. We want to determine exactly how did it get warm? What atmospheric conditions led to its warmth?

And that's a harder question, but you know, in one sense, a Co2, hydrogen atmosphere probably one idea is perhaps that you wouldn't expect that much oxygen, if at all in such an atmosphere, so there are markers. There are these things called banded iron formations that formed on the early Earth that just required some oxygen. Not a whole lot, but some oxygen in the atmosphere, or at least near the ocean and then you know, you can get reactions either abiotic [00:14:00] or biotic. That's debated. And form these, these iron bands.

So, you know, one thought is perhaps maybe you wouldn't expect to see those sorts of formations on early Mars if it was very oxygen poor. Some people would say, "Well, you know, on a warm early Mars, you know, with say an ocean in the northern hemisphere, which is what some of us like to say, that would be a good environment. If there's just a little bit of oxygen in the atmosphere, maybe that would be enough to get you these banded iron formations. Because these banded iron formations that we see on the Earth formed these ocean basins in the past. So maybe you would get them. So it's not clear, actually, which way that would go. But if we are able to determine Mars was a warmer planet and we confirmed it was an ocean there, but there's no oxygen, then that would give weight to the highly reducing or oxygen poor atmosphere that was hydrogen [00:15:00] rich. So, it's uncertain, but that's highly debated. It's a very complex problem.

Mat Kaplan: Hmm. A lot more to learn. Of course oxygen, it wouldn't be definitive evidence that there was or is life on Mars, but it wouldn't hurt to find some or evidence of past oxygen. Um, and that leads us to your third question and it is of course the big one. Did or does life exist on the red planet? Are we closing in? Are we getting closer? Now particularly with looking forward to the 2020 rover, now known as Perseverance and Rosalind Franklin which sadly we've learned is going to be a couple of extra years getting there while the European Space Agency and the Russians iron out the kinks.

Ramses Ramirez: Yeah, unfortunately, yeah. It's getting postponed. I think maybe it's due to the or partly at least this current epidemic, but um-

Mat Kaplan: Not helping.

Ramses Ramirez: Yeah, that's definitely not helping. As far as this question about did life exist or life, does it currently exist [00:16:00] on Mars, that's a ... That's the big million dollar question right there. You know, I said earlier if Mars was warmer and wetter and had a thicker atmosphere, as a lot of atmospheric and geologic indicators seem to imply, then that certainly would have fostered the conditions, uh, uh, especially if there was with liquid water evidence also that we're seeing, that would have fostered, uh, the conditions necessary for the emergence of life. And perhaps we'd be able to find evidence in the way of fossils uh in the rock record, but that's uh, that would probably require a man mission to send folks there. Planetary geologists and planet paleontologists that can dig up the surface and see if there's any evidence of fossils. Uh, which would be very cool if we found them. Because that would-

Mat Kaplan: Wouldn't it?

Ramses Ramirez: That would suggest a second ... I mean that would have extreme implications because if we able to, especially determine that life had emerged [00:17:00] independently, the suggestion would be on an exo-planetary scale that perhaps life is relatively common if two planets in our solar system, the first two that we begin to deep, dig deep, we find fossils that least microbial life or some sort of primitive life is pretty common in the universe. So, that's really cool.

Mat Kaplan: It's a much better sample than a sample of one, isn't it?

Ramses Ramirez: Exactly. It definitely would at least prove that life is possible outside of our planet, which has very strong scientific and philosophical implications. We don't think that there's life on the surface of the present Mars because it's pretty sterile, but there could very well be. Not just fossils, but actual living creatures underneath the surface that are shielded away from the radiation. So we, you know, little microbes or something that we'll have to prove, but I think we'll be able to show that pretty soon, in the next several years or so I hope we'll be able to [00:18:00] make headway on that question.

Mat Kaplan: You and me both and probably everybody who listens to this show. Of course, there are those, we won't have time to go into this particularly, but you do mention in the article, there are those who believe that we already found micro fossils that came from Mars on ALH84001, that mysterious uh meteorite. But, we'll save that for another time. Are you one of those who like pretty much every other scientist that I've spoken to, believes that the holy grail, at least for robotic exploration is still sample return?

Ramses Ramirez: I certainly think, you know my opinion of the holy grail is sending people there.

Mat Kaplan: Yeah, that, that's why I included the word "robotic," because I know how you feel about boots on Mars. We're going to get to that in a second, but okay, but short of people.

Ramses Ramirez: Yes. Well, short of people uh, sample return could definitely be, I would have to agree that that's probably the best thing that we can do aside from [00:19:00] remotely analyzing you know samples spectroscopically or what not, but yeah, sample return would be the next best thing we can do aside from actually sending people there. I would agree with that.

Mat Kaplan: Let's get to humans. You wrote a great 2018 blog post for Scientific American that I read at the time, didn't realize I'd be talking to you a year and a half, couple years later. You called it, Forget the Moon. So you apparently think, or I should ask if you still think that we humans ought to be exploring Mars alongside our robots. I mean it seems pretty clear that you think that ought to be our target.

Ramses Ramirez: Yeah, certainly when I wrote that article there was certainly a large of tension in the community. There still is about whether we should go to Moon or Mars first. I definitely prefer Mars. I think, you know, we do have technology to go there and carefully, I think we can have a successful scientific mission there, sending people there. But I can understand the value [00:20:00] of the Moon as well. Wherever you know, we decide to go,

Ramses Ramirez: ... of the moon as well. Wherever we decide to go or do, if we're going to do a Moon mission first or a man, a mission to Mars first, you know, I'm on board with either one, but I just, my preference is, uh, from a scientific return mission and I think Mars has even more potential. That was really the point behind that article.

Mat Kaplan: I'll say what I've said in the past. I sure hope I'm around to see, uh, those first men and women, uh, set foot on the, on the Red planet, uh. Ramses been great talking with you. I gotta ask you one more question though. How'd you end up in Japan?

Ramses Ramirez: Oh, this is, uh, an interesting question. The Earth's life sciences too where I'm working at right now is just a, uh, I've been keeping my eyes on them for a long time, ever since I was PhD student. And you know, I think they do a lot of great work here. We have, uh, it's really, it's an astrobiology Institute and as you know, as I've discussed throughout this, the show, it's very important to, to have an interdisciplinary approach for these [00:21:00] types of origin of life and life problems, astrobiological problems. And the Institute specializes in that. Came here, gave some interviews, they really liked me and I, uh, I'm now a scientist here. I just really feel in line with the philosophy of the Institute.

Mat Kaplan: That's great. Sounds like a pretty adventurous as well. I mean, if you had the chance, would you, uh, leave Japan and be part of that first mission to Mars, be the astrobiologist, uh, with a, with a pickax and looking for those fossils?

Ramses Ramirez: Yeah, sure. If, if, you know-

Mat Kaplan: [laughs].

Ramses Ramirez: [laughs]. I were, you know, if, if, if I were called to, to do something like that, yeah, that would be great for humanity. I would, I would say. Yeah. Um, [laughs] I would definitely, uh, uh, be among those, uh, trying to look at these rocks and features and seeing what we can find. There's a lot of hypotheses. I definitely want to test some Mars, so if nothing else, if I can't go, at least, you know, I'd be able to guide or give my advice as to what scientific [00:22:00] direction should be taken on the Red planet.

Mat Kaplan: Ramses you've got my vote if, if anybody asks.

Ramses Ramirez: Thank you.

Mat Kaplan: Um, thank you. It's been great fun talking to you and, um-

Ramses Ramirez: Thank you Mat.

Mat Kaplan: Let's, let's go to Mars.

Ramses Ramirez: Yes, definitely. I agree with that [laughs]. Amen.

Mat Kaplan: That's planetary scientists and astrobiologist Ramses Ramirez. We'll shift to our more distant neighbors, the giant outer planets in a minute. Please help me welcome a new sponsor to Planetary Radio with it comes a heady opportunity for all you creative plan RAD listeners. This time it's genuine rocket science. I know because I've got a bottle of it.

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Kunio Sayanagi is an associate professor in the Hampton University department of Atmospheric and Planetary Sciences. Kunio thanks for joining us on Planetary Radio. As we've worked our way out through the solar system, we have finally [00:24:00] reached those big outer planets and you start your article right off by saying that learning about these worlds, the four of them Jupiter, Saturn, Uranus, and Neptune really means learning about every discipline within planetary science. Can you talk about that?

Kunio Sayanagi: Yes. The other planets have 95% of the planetary mass in the solar system and it covers every discipline of planetary science. My favorite, of course is atmospheric science because I specialize, specialize in the atmospheres, but of course the outer planets have many moons as well. Each of those moons offer an opportunity for serious geology, exotic geology that that can be compared to all other bodies in the solar system. And of course, Jupiter has the strongest magnetic field of all planetary bodies, so that offers a lot of science as well. And on, on, on top of that, each of the four giant [00:25:00] planets has extensive systems of rings. Each of the rings is a prototype for the protoplanetary disc where all the planets formed.

Of course protoplanetary disks happened long time ago and we can't see those locally now. But rings offer an opportunity where clumps of ring particles meet and grow and possibly form new satellites in those rings. And the outer planets captured the first materials that the protoplanetary disk had, so by studying the composition of the outer planets, we can study the original material that we had in our solar system.

Mat Kaplan: So much more to explore out there. We'll talk a little bit in a couple of minutes about what we've learned recently and what still remains to be learned and how we might go about doing that, the missions that are being talked about. Um, but [00:26:00] first I want to talk about the decadal survey process with you, which comes up very frequently on our show because you obviously agree with pretty much every other planetary scientist that it is a very important process.

Kunio Sayanagi: Yes, of course.

Mat Kaplan: You mentioned that even before the decadal survey process, you can look back more than 50 years and there were reports that, uh, that talked about these kinds of goals for, for first study of the outer planets. Apparently we have quite a, quite a history of curiosity about these worlds.

Kunio Sayanagi: When I started talking about the decadal survey or the writing about the decadal survey, I wanted to be precise, so I started reading some older document and I started to finding references to big survey that the National Academy did in 1965. As far as I can trace, that was the original point where scientists got together to formulate these big questions.

I was almost shocked that the three [00:27:00] questions really haven't changed since then. They are worded differently, but they, the three are about the origin of life and how life evolved. So that's one question. Another one is other source system formed and evo- evolved. And the third question is usually worded in many different ways of it, but it's, it is about present day processes. Studying how the processes are working today and still making the solar system evolve.

Mat Kaplan: I'm struck by the last part of that last question that you posed in the magazine. How do we get such diverse worlds, uh, because it'd be wrong to think of these, these four planets as, as being terribly similar. I mean, they obviously share some similarities, but you see, um, uh, plenty of reason, uh, to uh, identify them individually.

Kunio Sayanagi: Yeah, um, so we don't have to constrain ourselves to just to giant planets. I am a planetary atmospheric [00:28:00] scientist, so I am basically interested in weather and climate. Those are inherently present day processes but when we say weather, we can study it two different ways. Of course, earth offers a lot of opportunities. We live in this atmosphere so we can study a lot of things in situ. But to make progress we tend to study extreme events where we are challenging our knowledge, right?

So we can either wait for extreme things to happen on earth or we can seek out extreme things that are always happening from earth parameters and the relative to earth parameters, of course. And the giant planets offer big atmospheres. So they offer a lot of opportunities. And another thing I like saying is that planetary sciences, just like psychology, my wife is a psychologist by the way-

Mat Kaplan: [laughs].

Kunio Sayanagi: So I like saying that. In psychology you do not understand one person, one person to death to [00:29:00] understand human mind and behavior, right?

Mat Kaplan: Yeah.

Kunio Sayanagi: So in studying planetary weather, we don't just study one planet to say that we understand whether. We study all the planets we can study and try to understand underlying laws of physics that governs the weather.

Mat Kaplan: There are always surprises, aren't there? I mean, every time a mission has gone either to orbit a planet or to pass by one, we, we've talked many times on this program about the surprises that wait for us and, and frequently the theories that have to be rethought.

Kunio Sayanagi: Yeah. Um, my favorite example is the hexagon on Saturn.

Mat Kaplan: Yeah.

Kunio Sayanagi: Of course, and I, I just came off of the Cassini mission. I was an affiliate of the imaging science team, have you talked about the hexagon on this show before?

Mat Kaplan: Oh, many times, uh, both, uh, with Linda Spilker, the project scientist for Cassini, Linda is still, uh, the person, the individual who's been on the program more than anybody. And, [00:30:00] uh, not that long ago with the Carolyn Porco.

Kunio Sayanagi: Oh, great. My core specialties, atmospheric dynamics of the Zion planets so the hexagon on Saturn is one of my favorite features in planetary atmospheres. Um, the hexagon was found in Voyager data with the spacecraft flew by Saturn in 1980 and 81. The hexagon in the data, of course, it was not noticed until 1988 because it was in the polar reason and both of the probes, both of the Voyager probes flew by Saturn in the equatorial trajectories. So the hexagon was in the heart defined spot and those images. But in the 1988, there was a paper that got published and then that was very puzz- puzzling.

It took a long time to really come up, come up with an explanation. In 19- 1991, um, there was some theory papers that proposed, um, theoretical explanation for [00:31:00] those things. For the hexagon. But it was difficult to prove it was, it was not until 2010 and after when the computer simulations and became sophisticated enough to test those ideas and I've been a part of a couple of those papers. Basically it's a meandering jet stream.

Even in the Voyager data, it was very clear that at the center or the along the outline of the hexagon, there's a jet stream that's blowing eastward along the hexagon, hexagon outline. So we always knew that it was associated with a jet stream, but why it was meandering in the six sided shape was something where you couldn't really explain until the 2010s.

Mat Kaplan: I would bet them that you are just as fascinated by those six cyclones that, uh, have been imaged by Juno, still actively orbiting Jupiter that are Jupiter South pole. In fact, there is a [00:32:00] gorgeous rather stunning image of the cyclones in, in your article, in the planetary report.

Kunio Sayanagi: Yeah. So it's definitely puzzling that those cyclones do not merge. This is a knowledge we have from earth, Austin dynamics, by the way. So when we place vortices that are spinning in the same directions, they usually merge. That's what we would have expected at Jupiter when we place cyclones close to each other, any two would merge, but to find six of them together was a big sock at the beginning.

So I actually have a graduate student who's been studying the dynamics of that. I don't think he's found a case that found a way to keep them apart, but there is a postdoc at Caltech named Chang Lee. I think he just moved to Berkeley. Um, he found a way to keep the cyclones from merging. He just [00:33:00] presented the results at the AGU meeting last December and I think, um, I'd been waiting for that paper to come out.

Mat Kaplan: That's great to hear. And I wish we had more time to talk about what we've learned already, but we probably should go on to talking about the mission so that you're looking forward to in the next few years and you identify a, a several that you're, you're pretty excited about beginning with Europa Clipper.

Kunio Sayanagi: Sure. So that is what has become of what was the recommended by the last D. Kayla survey? The last, D. Kayla surveys, top three picks for a large class mission. These are the missions to be directed, uh, directed by NASA, managed directly by NASA. The top one is Mars Sample Return. That became a Mars 2020. The next one as recommended by the decadal survey, it was called Europa Jupiter Orbiter. It was an orbiter to orbit around Jupiter, but its main target was going to be [00:34:00] Europa. That is the Clipper mission that we are talking about now.

Mat Kaplan: And then of course the enormously exciting, not that Clipper isn't, a but Dragonfly, which is really fired the imaginations of so many people that that mission that uh, will be headed to Titan, although not for a few years yet.

Kunio Sayanagi: Yeah, it is part of the new frontiers program, uh, the program has supported a series of really exciting outer planet missions. The first one was a New Horizons mission. And then the second New, New Frontiers mission was Juno. It's doing really exciting science at Jupiter studying the atmosphere and interior, the latest excitement they're about to publish or they have just published, I haven't seen the paper, one of the core goals was to determine how much water Jupiter collected when it formed. That's going to tell us when and where Jupiter formed in the solar system so that [00:35:00] when the paper comes out that's going to be really exciting. And then of course the third one is OSIRIS-REx that's going to a near earth asteroids and then the fourth one is going to be Dragonfly.

Mat Kaplan: I want to mention at least in passing the European Space Agency's current preparation for the JUICE mission that Jupiter Icy Moon Explore another orbiter. I want to go further out in the solar system too and give some sympathy once again to pour a Uranus and Neptune and all those scientists who've been waiting for us to visit those outer planets once again, what would you like to see happen at one or both of these worlds and not just you, but what is being talked about in the community?

Kunio Sayanagi: Among the planets, Uranus and Neptune are the only ones that have not been visited by an orbiter. Uranus and Neptune have been visited by Voyager 2, Oh, I was in the second grade, I was, I was attending school, primary school and Japan. [00:36:00] When I started hearing the news on the radio and on TV about the Voyager 2 fly by of Uranus, I started asking a lot of questions to my parents about a Uranus and what Voyager 2 was doing out there.

And my parents eventually just got really tired of me, so they just handed me the day's newspaper. My family was subscribed to something equivalent of the New York times. Um, [inaudible 00:36:27] Shimbun, that would be the Japanese economy newspaper. So it's a thick stack of paper. Right? And so they just handed me the day's newspaper and just told me to start reading when I was seven. So I actually did. So when my parents noticed that I was actually reading and I could finding it exciting, um, they just gave me a blank notebook and showed me how to cut out the article, and I actually still have the article.

Mat Kaplan: Oh, that's great.

Kunio Sayanagi: Yeah. And then-

Mat Kaplan: That's-

Kunio Sayanagi: Yeah, so that was a really busy year for, um, for [00:37:00] planetary science because after the Voyager flybys, within a couple of months, the um, Comet Halley flew by, um, came close to the earth. Right? So there were a lot of articles back then about, um, the comments. So I really quickly filled up that first note again, I still have it and it's one of my treasures.

Mat Kaplan: What a great introduction to planetary science. Now it's now to your profession. Would you like to see an orbiter out there at either Uranus or Neptune or maybe both?

Kunio Sayanagi: Both. Definitely. As an atmospheric scientist, I do not have a preference on Uranus or Neptune. I would love, love to see both because what's interesting about the difference between Uranus and Neptune, Uranus as far as we could tell within the precision of Voyager 2 instruments, Uranus was not emitting any heat, but Neptune was emitting a lot of heat. Uh, what's interesting about all the other planets is that other than Uranus, all of them emit more heat than they received from the sun. [00:38:00] Each of the planets is a ball of gas of course.

All four planets are shrinking in size very slowly. Each of the planets, when the original gas cloud collapsed into a planet, they trapped a lot of heat. As they release the heat, the thermal energy, the gravitational energies are getting converted into thermal energy and then a thermal energy escapes from the planet and then the cycle continues. The gravitational contraction happens a bit more, the heat escapes to the surface and then gets radiated. So for Jupiter, Saturn and Neptune, there's a measurable escape of heat from the interior, but we cannot not see that for Uranus, that's the big mystery from the atmospheric sciences viewpoint. Why you're in this is not emitting as much heat, miserable heat.

For the scientists who are interested in the geology and the formation of the moons, Neptune is a very [00:39:00] interesting place because of Triton. Triton is believed to be a castroid Kuiper Belt Object or KBO. Triton and Pluto are similar in size, but we don't really have close enough observation to say what difference they may have. But Triton is believed to have formed in a similar way to Pluto. Studying any differences or simila- similarities between Pluto and Triton will tell us more about how KBOs and far out solar system objects may have formed an evolved.

Another interesting thing about Triton is that we saw plumes erupting from the surface during Voyager 2. There are different hypotheses about how those plumes are driven. Some people say that it's a sign of internal awesome, other people say that it's, it's a sign that the solar [00:40:00] heating causes surface to evaporate sometimes it gets trapped-

Heating causes surface of operation that gets trapped below a layer of ice, and they might be blowing up from the surface. So we don't know the source of energy for those plumes. [inaudible 00:40:11] by Triton and making close observations, we should be able to tell the source of energy that's powering those plumes on Triton.

Mat Kaplan: Besides, it's a spectacular landscape and it would be nice to get some closeup, uh, shots of it, uh, to follow those, uh, that were delivered by Voyager 2. Very briefly, there has been much talk of a Europa Lander that could follow the Europa Clipper to that- that very promising moon, um, and you mentioned this in your article as well.

Kunio Sayanagi: Yeah. So two places we have a really good chance of finding present day life, um, outside of Earth are Europa and Enceladus. Europa, as you said, is the moon of Jupiter, and Enceladus is the moon of Saturn. [00:41:00] Both places are really exciting because they offer a subsurface ozone that are easy to access. Europa's ice thickness is ex- expected to be maybe two kilometers in some spots that might allow some exchange of material between surface and the ozone. So if we land on the surface, we might be able to tell what might be in the ozone that's under the surface. And of course, Enceladus is really exciting because it's blowing up material from the subsurface ozone into space through the geysers and near the south pole.

So if we could fly through the plume, um, that's blowing out of the south pole, we might be able to sample the ozone material without landing and see what might be in the ozone.

Mat Kaplan: Well, let's hope that we get such, um, intriguing data back from Europa Clipper that- [00:42:00] that Europa Lander, if it's not already funded by them, that, uh, that, that will give plenty of encouragement to, uh, the people who control the, uh, the- the wallets, uh [laughs], to make that mission happen.

There's much more in the article that we could talk about. Uh, I'll just encourage people once again to go and read the digital version of planetary.org. Of course, Planetary Society members, uh, should, by now, have had the beautiful, uh, printed version. One more thing that you talk about is the need for more probes that would drop down through the thick atmospheres of these- these, uh, giant gas worlds. And you've proposed a plan for- for doing just this. Can you tell us about- about SNAP?

Kunio Sayanagi: Yes. SNAP stands for Small Next-generation Atmospheric Probe. It has a design that offers multi-probe missions to the outer planets. We have had two atmospheric probes, um, that's sent to the outer solar system. The first one was a Galileo probe that went into [00:43:00] Jupiter in 1995, and the second one is the Huygens probe that went into Saturn's moon, Titan. Each of those is a single probe that made measurements at a single place, single location on each of those bodies. Some speculations have been that some of the things we measured at those planets are unique to the local location these probes just happen to go into.

A way to prevent that kind of controversy is to have multiple probes visiting, um, future planet, Uranus and Neptune, perhaps, uh, at multiple locations. If we can sample multiple locations, we can differentiate global properties from local variations. Traditional probes, like Galileo probe, are over 300 kilograms in mass, but SNAP design is only 30-kilogram in mass.

Mat Kaplan: Mm.

Kunio Sayanagi: We do that by [00:44:00] focusing on measurements that might return reasonable variations. It just so happens that measurements that are not expected very [inaudible 00:44:09], I guess, um, spatially, those measurements require big instruments, namely the mass spectrometer is the biggest one. The main target of mass spectrometer is noble gas concentration and isotopic ratios of different elements. Those parameters are not expected to vary. That means regardless of where we go in- in- go in, in the atmosphere, those measurements should not vary their results. By focusing on other measurements that are sensitive to local weather, basically, pressure, temperature and humidity, humidity, when I say humidity, by the way, it's not just water.

Mat Kaplan: [laughs].

Kunio Sayanagi: There are a lot more condensables than just water on the other planets. When we measure these, um, quantities, we are basically measuring, making [00:45:00] local weather measurements that might depend on the location. Um, SNAP is going to offer a way to explore multiple locations on these planets in the future.

Mat Kaplan: You remind me that one of the problems with the Galileo probe is that it just had bad luck that, uh, as we've talked about a couple of times on the show, it- it simply came down in a spot that was not typical of, uh, of a lot of the Jovian atmosphere. So, uh, you can see the- the d... real advantage of having a lot of these probes to drop into different locations.

Kunio Sayanagi: Right. Galileo probe really was a planetary all in one.

Mat Kaplan: [laughs].

Kunio Sayanagi: So it went into a feature, weather feature on Jupiter that usually covers 0.5% of the planet's surface. One of the main goals of the Galileo probe was to measure the water abundance on Jupiter but it went into a hole where we, uh, we already knew that there wasn't much water. So...

Mat Kaplan: Sort of a dry well [laughs].

Kunio Sayanagi: That's [00:46:00] right. That's how- that's how the... we're so excited about, um, the measurement that the Juno team is about to publish, the results we are waiting to see from Juno, but it will be nice to have one in situ confirmation to validate Juno's data. So that's one reason I, um, I said in my article why another probe to Jupiter would be valuable.

Mat Kaplan: So much more to learn. We have to hope that, uh, the scientific community, the planetary science community, and the decadal survey will continue to push for these missions to, uh, the giant outer worlds of our solar system. And that, um, we'll be able to come up with the wherewithal to, uh, get these missions funded and learn more about, um, this still mysterious portion of our- of our solar system. Kunio, thank you for taking us on this little tour of the, uh, the outer planets, and, uh, the plans that you and others have to, uh, to explore them further. I hope that we'll [00:47:00] have more to talk about and, uh, best of luck with- with everything that you're up to, including, uh, development of this concept called SNAP, the Small Next-generation Atmospheric Probe.

Kunio Sayanagi: Thank you. I enjoyed the interview as well.

Mat Kaplan: Planetary scientist, Kunio Sayanagi. After a quick break, we'll wrap up our survey of the solar system with its smaller worlds and bodies.

Debra Fischer: Hi. I'm Yale astronomer, Debra Fischer. I've spent the last 20 years of my professional life searching for other worlds. Now, I've taken on the 100 Earths project. We want to discover 100 Earth-sized exoplanets circling nearby stars. It won't be easy. With your help, The Planetary Society will fund a key component of an exquisitely precise spectrometer. You can learn more and join the search at planetary.org/100earths. Thanks.

Mat Kaplan: I saved our smallest but most numerous class of solar system objects for last because they are everywhere. Maitrayee Bose is a [00:48:00] cosmochemist and assistant professor at Arizona State University's School of Earth and Space Exploration. She's also on the steering committee of NASA's Small Bodies Assessment Group, or SBAG.

Maitrayee, thank you so much for joining us on Planetary Radio, uh, to talk about, well, what's left in the solar system after talking about, uh, everything else with your five colleagues who also wrote for the current issue, the Planetary Report. It's time to talk about small bodies, and what you cover in your article and maybe a little bit more. You start by reviewing so many terrific missions that have taken place over, what, maybe the last 20 years, maybe less than that. Seems like a really good time for those of you who want to learn more about these smaller citizens in our solar system.

Maitrayee Bose: It's a pleasure to be here. Yes, I did cover a few of them in the introduction of my article. There are the more recent ones, I would say. [00:49:00] But there has been in the past 10 years, you know, a dozen visits, flybys, to several asteroids. And we saw how they look, whether they have craters on the surfaces, whether the surfaces are smooth. So we learned quite a bit from several different flybys.

Mat Kaplan: What have we learned about the surfaces and the shapes of- of these asteroids, thanks to these missions?

Maitrayee Bose: The most recent one, I would say, uh, was the JAXA mission to this asteroid, Itokawa. Uh, we brought back samples from this particular asteroid, uh, but we were also able to map an image the surface quite a bit, and what we found was that Itokawa is a rubble-pile asteroid. Now, what I mean by that is you have these rocks and boulders, you know, a meter, 10-meter size boulders, that are just loosely held together by gravity. Uh, that's pretty [00:50:00] insane, right? I mean, you're looking-

Mat Kaplan: [laughs].

Maitrayee Bose: ... at these asteroids, uh, they should be these single, uh, little solid body, but they're not.

Mat Kaplan: When I was a kid growing up, all we saw were these big rocks in space that were obviously not piles of rubble.

Maitrayee Bose: Right, right. And in fact, some of the asteroids, uh, you know, [inaudible 00:50:18] of the asteroids aren't like that. So, you know, it's not just that every asteroid that we look at are rubble piles, but I would say most of them would be. And that says something about what was happening very early in the solar system. So you can imagine that there were collisions happening a lot more than what we see now, and these collisions would lead to breakup of the bodies, but then gravity takes over and puts these bodies together into what we see.

Mat Kaplan: What I should've said, of course, is that when I was a kid, we weren't seeing pictures of actual asteroids because there weren't any, until-

Maitrayee Bose: [laughs].

Mat Kaplan: ... some of these recent missions, and- a- and some radar work, we should say. But in the artist concepts, [00:51:00] they were always these big, rugged rocks. What about the shapes of these? I mean, you- you point out something that has come up on the show before. Were you surprised to see that some of them look quite similar to one another? Or are we looking at, you know, new mechanics of- of how these rubble piles, uh, come together and what they look like when they do?

Maitrayee Bose: That's correct. So, Itokawa, like I mentioned, is a rubble pile. The shape is this diamond shape. It's like... it looks like a top, uh, almost that's spinning, and that shape is very unique because two other asteroids that we are currently visiting, uh, Bennu and Ryugu. Bennu is an asteroid that we will have samples from very soon. With Ryugu, it's a Japanese mission again, the second Japanese mission. And they have already collected the samples and they're on their way back. Now both these also look like these top shaped asteroids. So there is some similarity in the shape, [00:52:00] which says something about the process by which they are made.

Mat Kaplan: You mentioned something called the YORP effect, Y-O-R-P, which, uh, uh, may have a lot to do with- with, uh, these shapes that we're seeing. W- what are we talking about here? What does that mean?

Maitrayee Bose: Yes. You could imagine that you have a small body that is light is getting scattered off the surface of this body, uh, but it's also emitting some of its own common radiation. So, you have the sun's light coming in, some of it gets absorbed, and then a lot of it gets emitted. This process is different depending upon which phase of the asteroid is hitting the sun's rays. And so that leads to changing of the rotation period of these asteroids. So you have these tops that actually spin up or, over time, can spin down. And this spinning up and spinning down process can [00:53:00] then lead to this top shape that we observe.

Mat Kaplan: Huh. Man, I wish we had more time to talk about this. We'll continue, of course, to talk about small bodies, uh, and, uh, we'll continue to talk about OSIRIS-REx, uh, which, uh, is still making those preparations to pick up that sample at, uh, at Bennu, something that, uh, comes up on the show quite a bit. Let's look farther out in the solar system, mostly, I suppose, to the New Horizons mission that, of course now, has done its work at Pluto, and, uh, has, uh, this other object, now officially named Arrokoth, I hope I have that right. Arrokoth surprised some people, or at least have surprised me because it looked like some other things that we've seen, um, a- around the solar system, notably, uh, some comets, like the- the one visited by Rosetta.

Maitrayee Bose: Yeah, yeah. It's- it's actually true. The... it does look very much like some of the cometary nuclei. Although, I would have to say, that the cometary nuclei, we don't think, are [00:54:00] contact binaries-

Mat Kaplan: Mm.

Maitrayee Bose: ... uh, which Arrokoth is. And so what do I mean by a contact binary? So we're talking about they could be rubble pile, but the material is much more icy and clay in nature than rocky. You can consider two of them that are in close association with each other and they collide at very, very slow speeds, enough to just stick, and that's what we're seeing with Arrokoth.

Mat Kaplan: I wanna turn to the three questions that you posed, as did your colleagues, in the Planetary Report with their articles. The first of these, are asteroids and comets primordial bodies, meaning are they building blocks of planets? And I believe that this is an area in which you take a lot of personal interest and where a lot of your research is focused?

Maitrayee Bose: Yeah, that's right. So the... this first question is mostly aimed at understanding how planets form, whether these small bodies that we see in our solar system was what built the planets. [00:55:00] Because there is another school of thought that talks about these small bodies being just remaining material from the planetary formation process. Now if we look at very pristine meteorites, we see it does have ingredients that can make a planet. So, in meteorites, for example, you have chondrules, calcium-aluminum inclusions, very pristine, organic matter, all those are still present, which is why there is this large family of cosmochemists who think that they are primordial bodies.

Now, I am interested in understanding how much water has been incorporated in these asteroids while they were forming and if this whole idea that planets form from asteroids is true, then we can estimate how much water was then, uh, delivered or was present as collisions between asteroids form these planets.

Mat Kaplan: So we're still [00:56:00] following the water at least as far as small bodies go. How do you conduct this research? Are... do you work with the data from these missions?

Maitrayee Bose: Not directly. So with, uh, the Hayabusa mission to Itokawa, uh, they brought back samples and we have some of those samples in our lab. And I-

Mat Kaplan: Hmm.

Maitrayee Bose: ... just use the volatility techniques to measure volatiles in some of these tiny, tiny particles. I use this instrument called the NANOSENS, uh, which is a secondary [inaudible 00:56:30] spectrometer that can measure elements at very, very high spatial resolution. So we have some of these particles that are 50 to 100 microns in size, so just-

Mat Kaplan: Mm.

Maitrayee Bose: ... to give you an estimate of how small that is. Diameter of human hair is typically 100 to 500 microns in size. So we have particles that are really tiny and we are trying to measure some of them in my lab.

Mat Kaplan: I am so impressed that with as... the small as that sample was that was, uh, returned by Hayabusa, [00:57:00] you must feel very fortunate that you were able to get even this tiny amount, uh, to, uh, put in your instruments.

Maitrayee Bose: Oh yeah. I- I... it's... it has been an amazing experience working with some of these samples [inaudible 00:57:13] because we have to devise new ways to even mount them, right?

Mat Kaplan: Mm.

Maitrayee Bose: We cannot... we get these loose particles, we have to find a way to not lose them because there is, you know, static electricity everywhere. So, you know, you have to have very specialized equipment that can take some of these tiny particles at the end of their needles and put them in material that can be then mounted and put into the instrument. Thankfully, at ASU, we have a host of, uh, lab equipment that can do nano scale measurements.

Mat Kaplan: Maitrayee, I'm putting your lab on my bucket list so that I can-

Maitrayee Bose: [laughs].

Mat Kaplan: ... [laughs] take a look at, e- even if it's under the microscope, at some of these tiny fragments from so far away, uh, because, you know, I've- I've gotten to see ALH84001, [00:58:00] I've seen, uh, pieces of the moon, but, uh, now I- I wanna see some of Itokawa. Um...

Maitrayee Bose: Yeah. No, absolutely. I mean-

Mat Kaplan: [laughs].

Maitrayee Bose: ... once this- once this pandemic is over, I would welcome you to my lab. In fact, there was supposed to be two visits, uh, you know, one of them from PBS NOVA, which [inaudible 00:58:17]-

Mat Kaplan: Hmm.

Maitrayee Bose: ... has been delayed [laughs]-

Mat Kaplan: Oh.

Maitrayee Bose: ... because [inaudible 00:58:22] this pandemic that's happening. Whenever you're interested, just email me and I can show you some of Itokawa that we have mounted very, very carefully, and they are [inaudible 00:58:30] right now.

Mat Kaplan: I'm gonna take you up on that. I'll be in good company with NOVA, obviously. Let's go on to your second question, here it is, are there important differences among the different types of small bodies? Th- the obvious answer would I guess be, yeah, from what we've seen so far, but you go- you go beyond that. In particular, you point to a mission that is still a few years off, well into the period of the next decadal study, which, of course, is what inspired this whole series of, uh, of articles. [00:59:00] Tell us about Lucy and- and why it's going to help to answer this question.

Maitrayee Bose: Yeah. So Lucy, it's a NASA mission that will tour, uh, five Jupiter trojans, and some of them are actually binary asteroids, which so, you know, with a total of seven, uh, asteroids. This has never been done. We have never done a mission where we visited so many of the asteroids and looked at the surfaces, look for clues as to if they are different or similar. You know, that- that's the question. Are the Jupiter asteroids all been captured by Jupiter? Because Jupiter is so, you know, huge, right? It can capture it because of its gravity-

Mat Kaplan: Mm-hmm [affirmative].

Maitrayee Bose: ... which we think has occurred, but we need to prove that.

Mat Kaplan: Before we move out really even to visitors from beyond our solar system, I wanna- I wanna see if you have any comment about one other mission that, uh, a lot of us are looking forward to, and that's, uh, Psyche, which is going to, for the first time, visit a [01:00:00] kind of asteroid that nobody's been to before.

Mat Kaplan: Kind of asteroid but nobody's been to before.

Maitrayee Bose: Yeah, so this, that's a very, uh, important and a mission close to my heart because it is being led by people at ASU, from my school. Psyche is going to this metal rich astroid. We think that there was this proto planet, so before a planet forms, you have a smaller body that is just big enough to have an atmosphere of its own, can undergo defenestration, like [inaudible 01:00:34]. So it has a core, mantel and a crust. So you know, we think that there was this really large proto planet that got into a massive collision and got broken apart, such that we now have an exposed core. And that's the core of Psyche that they're going to visit soon, which is pretty, yeah, pretty incredible that we can do that.

Mat Kaplan: It's very excited. I mean, who knows when [01:01:00] we're going to, if ever, possibly never, reach the core of, uh, of a planet like earth. It's, it's, it's quite a daunting task. But to have this piece floating around out there, and now we've got a visitor going out there, it almost gives me chills.

Uh, tell you something else that gives me chills, it's your third question and the implications, what are the processes that dictate the orbital dynamics of interstellar objects? And as we know, it's only been what? Less than three years since the first of these. Oumuamua, well, not the first, only the first that we were able to confirm came from else where-

Maitrayee Bose: Right.

Mat Kaplan: Uh, was, was discovered and, uh, now we seem to be finding more. A couple years later and we get, uh, comet Borisov. Tell us about this and why it's important to study them.

Maitrayee Bose: You're absolutely right. There were probably a lot of these interstellar interlopers that came through our solar system but we did not have the technology to identify them quickly and move all our [01:02:00] telescopes to, you know, map them or whatever. So, right now we can do that very effectively, which you know, we are in an amazing age I would say in that sense. Now some of these objects, the way they are identified is because of the trajectory. There are very specific angles to which they are supposed to come in and we don't think that if it's a solar system body they would have that plot. That's like the easiest way to identify them.

But somehow, you know, in our minds, we always thought of interstellar objects of being different. Like, they should be somehow very different. They should look different or they should behave differently is what we had in our mind. And the two objects now that we've looked at, Oumuamua and Borisov, they both are different from each other, but they are similar in some sense to objects in our ar- in our solar system. Oumuamua is very, very special. It just has a weird shape, it's just very, very different. Borisov, however, does look like comets in our [01:03:00] solar system. Right? Icy, has a tail and so on and so forth.

All of these objects are so unique, but they can say something about where they are coming from and upon which direction, maybe from which, you know, galaxy. I mean, I don't know, this is just speculation, but hopefully with all the telescopes that we have and the new ones that are coming out with the [inaudible 01:03:22] observatory, uh, we'll be able to identify more of these and start classifying them and trying to then look for trends in how they look, uh, which would be very, very cool, I think.

I'm really looking forward to, you know, finding more of these first.

Mat Kaplan: Here I'm talking about the difficulty of reaching the core of a planet like earth, um, it is at least matched by, uh, the possibility of an interstellar mission, to go out there and [laughs] uh, do, uh, instant examination of, of another star system and yet here are there bits of other star systems, uh, coming right into our neighborhood. It's pretty [01:04:00] exciting. Let me close with this and I, I, I hope this isn't too far out of left field. We at least now have one visitor to the Kuiper Belt. Would you, some day, love to see something go out there much further into the Oort Cloud and, uh, take a look around there?

Maitrayee Bose: Absolutely. I mean, I think what I'm going to say may not happen in my life time, but-

Mat Kaplan: Mm. Or mine.

Maitrayee Bose: [laughs] Um, but what I would really like to see is a small probe, like a cube sat that sits on one of these interstellar interlopers and takes us to where it came from.

Mat Kaplan: Ah. I think we should push for that. [laughs] We know a little bit about cube sats at the planetary society, so what a tremendous idea. I'm gonna mention that to some of my colleagues.

Maitrayee Bose: You should. No I, I wish there was some way to do that and I, I think the European space agency with its comic interseptal mission is going to get there because initially we just have to make sure that they find [01:05:00] something and they go for it, right? Get as close to it as possible. But eventually, you know, if you can land on it and just be there sitting and let it take us wherever, that would be amazing.

Mat Kaplan: God, wouldn't it? And it seems like now, to me, such an obvious choice, but not something I'd ever heard of anywhere and, uh, I'm, I'm sure you're not the only person who's thinking about this, but I'm very glad to have heard this from you, and very glad to have had this conversation. Thank you for wrapping up our, our tour of the solar system as we look towards the formation of the, the next planetary science decadal survey. I've really enjoyed talking to you, uh, [Matraie 01:05:38].

Maitrayee Bose: Thank you, Mat, this has been amazing. Yeah, it's good to sort of dream about things, right? And, and learn about our solar system and objects beyond of course. Uh, but this has been a very, very nice conversation.

Mat Kaplan: Thank you, I think so too. My conversation with Maitrayee Bose: completes our whirlwind tool of the solar system. You [01:06:00] can read the articles by all six of our scientist authors in the Planetary Report. A digital version of the magazine is at planetary.org. While members of the Planetary Society have the beautiful printed version. Time for another shut in version of what's up [laughs] as we talk about ne- the night sky, as big as that. But, but here are Bruce Betts and me, stuck at home like so many of you.

Bruce of course, the chief scientist of the Planetary Society, how are you? How are you holding up?

Bruce Betts: I'm finally healthier I think, so that's a plus. Uh, being at home, I don't mind being at home. I like home. Right? Here comes the dog.

Mat Kaplan: [laughs]

Bruce Betts: And there goes the dog.

Mat Kaplan: And that's one of the things you like, I know.

Bruce Betts: [laughs]

Mat Kaplan: Um, and, I do want to make it clear to folks that, that as far as we know, you were not caught by the Covid-19 virus, this was just something else?

Bruce Betts: No, but I di- I don't know, and I wasn't [01:07:00] unhealthy enough to get tested considering the lack of testing around, so, uh, if-

Mat Kaplan: Yeah.

Bruce Betts: If they come up with an antibody test at some point that's available I will take it and we will know, but no, my symptoms were long and hanging on but, uh, mild in duration and I'm sure that's what everyone tuned into hear, so there you go.

Mat Kaplan: Well, may everybody else, uh, who is afflicted with this, uh, have no worse an experience than you had. Uh, we certainly, we certainly hope for that. And there's the dog hoping the same. Um, you, you, you may remember that we, we talked not long ago about a certain, uh, popular delicious breakfast meat?

Bruce Betts: Yes.

Mat Kaplan: This came from Mel Powell. He's, uh, suggesting this, uh, to you. As seen from earth, how many asteroids are within six degrees of asteroid bacon?

Bruce Betts: [laughs] Wow, I'll have to do a calculation. I'm guessing a lot.

Mat Kaplan: [laughs]

Bruce Betts: Now I'm gonna actually... dang it, now [01:08:00] I'm not going to get anything else done today.

Mat Kaplan: [laughs] He did mention, you know, to let you off the hook that of course they're always in motion relative to each other [laughs] so, you don't, you don't have to put too much time into this. Uh, what's up there, other than asteroid bacon?

Bruce Betts: Well there's asteroid sausage and asteroid eggs.

Mat Kaplan: [laughs]

Bruce Betts: No, no, there's actually a lot of stuff in the sky. I, I need to turn to a serious sky guy for a second. Hey there Mat, there's good stuff... [laughs] I'm just lost.

Mat Kaplan: That's way too serious.

Bruce Betts: I've lost my mind apparently. The fever. So, in the pre dawn east, we've got Jupiter, Mars and Saturn lining up or close to it. Mars is just nuzzled and snuggled past Saturn, so going from upper right to lower left, pre dawn east, you've got very bright Jupiter and then you have very similar in brightness, yellowish Saturn and then reddish Mars, so check that out.

[01:09:00] And in the evening sky, we've got Venus looking super bright over in the west, and it is going to be hanging out near the Pleiades cluster, so on April 3rd, it'll actually basically be crossing in front of the Pleiades, so very nice view. Also, check out the cosmic balance [laughs] I don't know, the cosmic balance-

Mat Kaplan: [laughs]

Bruce Betts: Between where you... Orion, which is in the south, uh, in the early evening, you got Orion's belt. If you go one direction, you get to the brightest star in the sky, if you draw a line through Orion's belt, that's Sirius, and then if you go the other direction, you at least kind of, you get the Venus, the brightest star like object in the sky. Pretty groovy, huh?

Mat Kaplan: I love it.

Bruce Betts: But wait, don't order yet. People may have been hearing there's a comet, Comet Atlas. It is hard to see right now, it's in the Ursa Major Big Dipper kind of area, but you need a telescope or binoculars. It is aways with [01:10:00] comets, we don't know how bright they're gonna get, so it may get bright enough to see it with the naked eye in mid to late May, uh, or it may disintegrate as it heads close to the sun, so we'll keep you posted.

Mat Kaplan: Keeping us guessing. That's what it's doing.

Bruce Betts: As comets always do. We move onto this week in space history, it was 2001 that the appropriately named Mars Odyssey was launched and amazing, Mars Odyssey orbiter is still working 19 years later.

Onto random space fact.

Mat Kaplan: Wow, I liked that.

Bruce Betts: [laughs] Um, I'm feeling powerful. In a continuation from last week, following a theme, if the earth and the sun were, I don't know, let's say six feet or about two meters apart-

Mat Kaplan: [laughs]

Bruce Betts: Then Neptune, that's the earth and sun, if they were that far apart, then Neptune would be a very safe approximately 60 yards or 55 [01:11:00] meters away.

Mat Kaplan: How appropriate. [Ola Francine 01:11:03] one of our many Swedish listeners, he says, "Remember that astrophotography is the best social distancing."

Bruce Betts: [laughs]

Mat Kaplan: [laughs]

Bruce Betts: Universal distancing.

Mat Kaplan: Yeah, six light years is a pretty good... you're probably safe at six light years.

Bruce Betts: Oh I, I think you're good.

Mat Kaplan: [laughs]

Bruce Betts: I think that's one thing that's actually certain.

All right, we move onto the trivia contest. We discussed white dwarfs and the Chandrasekhar limit, which is the maximum mass of a stable white dwarf star, assumed to be non rotating and I asked you in solar masses, what is the approximate value of the Chandrasekhar limit. How'd we do?

Mat Kaplan: I was so disappointed that I couldn't remember this number, because I used to know it by heart. But we had a lot of listeners who said this is one that they knew by heart. My, what a sophisticated group.

Bruce Betts: Yeah.

Mat Kaplan: And, and we had, we had responses from you name it, man. Australia, China, Siberia, [01:12:00] the aforementioned Sweden, from all over the place. It was Texas that our winner comes from this time. First time winner, though a perineal entrant, Paul Swan in, uh, Austin, Texas. He says that that Chandrasekhar limit is about 1.4 solar masses. Is he correct?

Bruce Betts: He is indeed correct. So if you got, uh, past that, depending on how much your, uh, white dwarf is rotating, uh, then you go past the electron degeneracy pressure limit and it squishes down into a neutron star or, um, if you get big enough, into a black hole. So yes. Sorry, long answer of yes, that's right.

Mat Kaplan: Well I'm so glad you mentioned those degenerate electrons because we have a poem from Dave Fairchild-

Bruce Betts: [laughs]

Mat Kaplan: Our poet lorette about that, degeneracy of electrons is what is used by a white dwarf to keep itself from collapsing into a black hole, a gravity well. Dark and deep. The limit is bound, Chandrasekhar has [01:13:00] found. The point the collapsing star passes is set on a scale above where it falls of 1.4 full solar masses. [laughs]

Bruce Betts: [laughs] Wow, that was impressive.

Mat Kaplan: Hey, I didn't tell you yet that Paul is going to get a Planetary Society rrrr- rubber asteroid. I had a little trouble getting the motor started.

Bruce Betts: [laughs]

Mat Kaplan: Uh, and a terrific book. Uh, I've been spending more time with this book. Its, uh, Spacefarers, how humans will settle the moon, Mars and beyond by Christopher Wanjek, published by Harvard University Press. It's, it's very entertaining and, uh, he goes out on a limb here and there making predictions about when we will settle some of these places, if we settle them. But it's very down to earth [laughs] as down to earth as a book called Spacefarers can be. Uh, and, he, he presents all the challenges as well, it's, uh, it's very good, I recommend it.

Here's some more stuff that we got from listeners. Another poem from, uh, Martin [Hajaski 01:13:56], Setting the Limit is what this one's called with [01:14:00] apologies, Martin says, to Dave Fairchild. Subrahmanyan Chandrasekhar, Chandra for short, was only 20 when a special formula did he exhort. Though elders objected, young Chandra did retort white dwarf's max is 1.4 solar masses. The math, did I sort.

Bruce Betts: [laughs]

Mat Kaplan: [laughs] Jean [Louin 01:14:21] who, who often also sends us great poems, but he said, "I'm amazed at the brilliant minds that can perform these astronomical feat." Isn't that incredible? I mean, we heard various ages, 19 or 20 for Chandrasekhar when he came up this, and it wasn't very well received but, uh, it turned out to be absolutely the way the universe works.

Bruce Betts: Yeah.

Mat Kaplan: Devin O'Rourke in Colorado, oh, only point four more massive than our sun? That's not so much. And then he realized that's still hundreds of times more mass than all of the rest of the solar system combined. [laughs]

Bruce Betts: Crazy. Crazy.

Mat Kaplan: B'Jorn [Getta 01:14:58], oh man it's been... we don't get enough [01:15:00] of these, uh, great special units that, uh, we sometimes hear from listeners. B'Jorn Getta says that, uh, 1.4 solar masses, that's about 1.67 times 10 to the 30th coronas. That's bottles of Corona. Beer. [laughs]

Bruce Betts: A standard unit.

Mat Kaplan: Bob Lee in New York, based on his estimation of your mass, 3.4 times 10 to the 28th Bruce Bet's.

Bruce Betts: That is, that is exactly right.

Mat Kaplan: [laughs] Ashley Anderson in Australia, I had never heard of this, a white dwarf won't collapse in a neutron star or a black hole above the ready? Tolman Oppenheimer Volkoff limit of 2.14 solar masses. Is that new to you? I mean you're a, you're a pro.

Bruce Betts: [laughs] I, I have heard all those names, even strung together, but it's been awhile.

Mat Kaplan: [laughs] I looked it up. There actually is something to this [01:16:00] so, uh, thank you for that, Ashley. And Ashley gets the last word. We're ready for next time.

Bruce Betts: Down to something serious. What mission played the first musician instruments in space?

Mat Kaplan: [laughs]

Bruce Betts: Go to Planetary.org/radiocontest.

Mat Kaplan: All right, so you're talking now about more than just the beep, beep, beep of, uh, Sputnik One?

Bruce Betts: [laughs] Yes. I'm talking about humans playing what would be standardly considered in some form, musician instruments in their space craft while in, in space.

Mat Kaplan: So humans, not a recording?

Bruce Betts: Not a recording, humans.

Mat Kaplan: All right, we got it, and you've got until Wednesday, April 8th, at 8 AM Pacific time to get us the answer to this one and, uh, because we are continuing our social distancing in, uh, head quarters for the Planetary Society is still closed down. Kind of... I'm disappointed too, dog.

Bruce Betts: [laughs]

Mat Kaplan: It's another opportunity for you to [01:17:00] win Bruce and or my voice, uh, an outgoing message for your, uh, voice mail system, uh, if you so choose, uh, that's what we have for you as the big prize this time, but that's it for now.

Bruce Betts: All right, everybody. Go out there, look up in the night sky and think about what degeneracy pressure you've over come. [laughs] Thank you and good night.

Mat Kaplan: Here's the pressure I've over come, it's that great line from the Graduate. You are a degenerate.

Bruce Betts: [laughs]

Mat Kaplan: And the electron said, "Thank you, thank you very much." [laughs] That's Bruce Betts giggling in the background. He's our chief scientist at the Planetary Society. He's all better now and so I'm very happy about that, uh, as he joins up every week here on What's Up.

Planetary Radio is produced by the Planetary Society in Pasadena, California and it's made possible by its members who want to explore our entire solar neighborhood. Join us by visiting [01:18:00] plantary.org/membership. Mark Hilverda is our associate producer, Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. Be safe, stay healthy everyone. Ad astra.