Planetary Radio: Space Exploration, Astronomy and Science - The Next 10 Years: Continuing our Solar System Tour

Episode Date: April 1, 2020

Our survey of the solar system in anticipation of the next planetary science decadal survey continues with Mars, the big outer planets, and the smaller bodies that share the neighborhood. Three more great scientists share their looks ahead. Staying responsibly stuck at home is easier when you can look up at a gorgeous night sky. Bruce Betts is here to help with another fun edition of What’s Up and a Random Space Fact or two. Learn and explore more at https://www.planetary.org/multimedia/planetary-radio/show/2020/0401-2020-next-10-years-part-2.htmlSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

What will the next 10 years bring the rest of our solar system? That's 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. 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 downlink are moments away. First, though, here's an opportunity I'm excited about. Our good friends 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 p.m. Eastern on April 1st, 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 System, has stopped due to COVID-19 restrictions. 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 reflight. A few days later, some SpaceX 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 the other fun and informative features of this week's Downlink are online at planetary.org slash 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.

Ramesses 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. Ramsey, 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 sick 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. Thank you. And I'm very glad to be here, Matt. Well, it's obviously a subject you care a lot about. We found the water up there on Mars. We know more or less now where the atmosphere went. Kudos to the MAVEN orbiter. We've even found organics. What's left on the red planet for us to discover? Oh, there's really a lot to discover on the red planet. We just barely scratched the tip of the iceberg. Like you've said, MAVEN has brought in a lot of good information about assessing the atmospheric 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 early climate of Mars because then 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 kind of like you can think of them as like Grand Canyon-like features that required a lot of water. So there's a lot of evidence that Mars used to be a more Earth-like planet in the past with a thicker atmosphere. What MAVEN was able to tell us was or infers 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 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. 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? Yeah, that's actually, that's the interesting thing is that those estimates are really only a lower bound estimate. Wow. 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 strong thermal escape mechanisms,

other escape mechanisms that would have been present in the past that, you know, it's not easy to tease out of the MAVEN analysis that could have led 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. 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 habitable back then, at least to life as we know it, put that in quotes. And it's habitability that you obviously care a great deal about. I mean, your website, habitableplanets.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. Yeah, this is a new term based on some astrobiology reports that scientists have put together the past year or two 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. 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 the 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 Mars 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 on the verge of a renaissance or a renaissance of knowledge.

Sounds like planetary science, which is by definition multidisciplinary. That's right. Sounds like planetary science, which is by definition multidisciplinary. That's right. Let's pick up the three questions that you chose for Mars, the big questions 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 atmospheric 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. Yeah, this is an interesting idea that is 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 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 models, 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 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 SO2, methane, other possibilities. And a lot of these have issues. 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 polymerizes and becomes very refractive. And once it gets warm and you start to rain, it actually rains out of the atmosphere. Methane also has issues with stability of the atmosphere and other things. Hydrogen, we proposed that to be the other gas next to CO2 that would have been important on early Mars, primarily based on meteoritic evidence, suggesting that Mars used to probably outgas a lot of this stuff. A lot of volcanism on Mars, probably 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 inferred that the early atmosphere on Mars could have likely also been hydrogen rich. atmosphere on Mars could have likely also been hydrogen rich. And it just turns out because of the radiative 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 and 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, you'll be able to excite these transitions and have that combined molecular pair of CO2 and hydrogen to absorb very strongly. So that's what's going on there. An intriguing model, but how will we go about determining if this was actually the nature of the Martian atmosphere a billion or so years ago or more? Yeah, this is a very good question. And it's something that we will have to actually, you know, I think that with the Mars 2020, maybe we'll get some answers. One thing you want to answer before even answer the atmospheric composition is, you know, whether early Mars was warm or cold. So there is still that lingering debate.

Yeah. And that's your second question that you posed, 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? Exactly. And essentially what Mars 2020 can do in future Mars missions is start assessing, the rovers can assess these terrains and look for evidence of icy features. So far, rover missions we have at Gale and the orbital missions have not found any convincing evidence of an icy early Mars, which gives more weight to the idea that Mars was probably not that icy. It was a pretty warm planet in the past.

So we need to continue those analyses 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 in one sense, 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 or biotic, that's debated and form these iron bands. So 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, on a warm early Mars 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 that Mars was a warmer planet and we confirmed there was an ocean there, but there's no oxygen, then that would give way to this highly reducing or oxygen-pouring atmosphere that was hydrogen-rich. So it's uncertain, but that's highly debated. It's a very complex problem. A lot more to learn. And of course, oxygen, it's not, 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. 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? Particularly with, you know, looking forward to the 2020 rover, now known as Perseverance, and Rosalind Franklin, which, you know, sadly, we've learned is going to be a couple of extra years getting there as the European Space Agency and the Russians iron out the kinks. Yeah, unfortunately, yeah, it's getting postponed. I think maybe it's due to the current, partly at least this current epidemic, but- Not helping, yeah. Yeah, that's definitely not helping. As far as this question about did life exist or does it currently exist on Mars, 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, that's the big million-dollar question right there. 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, especially if there was liquid water evidence also that we're seeing, that would have fostered the conditions necessary for the emergence of life. And perhaps we'd be able to find evidence in the way of fossils in the rock record. But that would probably require a manned 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,

which would be very cool if we found them. Because that would suggest a second. I mean, that would have extreme implications. Because if we were able to especially determine that that life had emerged independently, the suggestion would be on an exoplanetary scale that perhaps life is relatively common. If two planets in our solar system, the first two that we begin to dig deep, we find fossils, that at least microbial life or some sort of primitive life is pretty common in the universe. So that's really cool. It's a much better sample than a sample of one, isn't it?

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 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 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 make headway on that question. 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 microfossils that came from Mars on ALH 84001,

that mysterious meteorite. But we'll save that for another time. Are you one of those who, like pretty much every other scientist I've spoken to, believes that the Holy Grail, at least for robotic exploration, is still sample return? I certainly think, you know, my opinion that the Holy Grail is sending people there. I think- Yeah, 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. Yes. Well, short of people, sample return could definitely be, I would have to agree that that's probably the best thing we can do aside from remotely analyzing samples spectroscopically or whatnot. But yes, sample return would be the next

best thing we can do aside from actually sending people there. I would agree with that. 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, a couple of 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. Yeah, certainly. When I wrote that article, there was certainly a lot of tension in the community. There still is about whether we should go to moon or Mars first. I definitely prefer Mars. I think 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 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 from a scientific return mission. I think Mars has even more potential. That was really the point behind that article. I'll say what I've said in the past. I sure hope I'm around to see those first men and women set foot on the red planet. Ramsey's been great talking with you. I got to ask you one more question, though. How'd you end up in Japan? Oh, this is an interesting question.

The Earth Life Sciences Institute, where I'm working at right now, is just a, I've been keeping my eyes on them for a long time ever since i was a phd student and you know i think they do a lot of great work here we have uh it's a really it's an astrobiology institute and as you know as i've discussed throughout this the show it's very important to have an interdisciplinary approach for these types of origin of life and life problems astrobiological problems and the Institute specializes in that. I came here, gave some interviews. They really liked me,

and I'm now a scientist here. I just really feel in line with the philosophy of the Institute. That's great. Sounds like pretty adventurous as well. I mean, if you had the chance, would you leave Japan and be part of that first mission to Mars,

be the astrobiologist with a pickaxe and looking for those fossils? Yeah, sure. If I were called to do something like that, yeah, that would be great for humanity. I would say, yeah, I would definitely be among those trying to look at these rocks and features and see what we can find. There's a lot of hypotheses I definitely want to test on 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 direction should be taken on the red planet. Ramses, you've got my vote, if anybody asks. Thank you. It's been great fun talking to you, and let's go to Mars.

Yes, definitely. I agree with that. Amen. That's planetary scientist and astrobiologist Ramsey's 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 PlanRad listeners. This time it's genuine rocket science. I know, because I've got a bottle of it. Rocket science proprietary red wine comes from the pioneering Caldwell Vineyard in Napa. Red wine hasn't always been my first choice, but I'd never had rocket science before.

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Kunio, thanks for joining us on Planetary Radio. As we've worked our way out through the solar system, we have finally 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? Yes. The outer 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 in the atmospheres. But of course, the other planets have many moons as well. Each of those moons offer an opportunity

for serious geology, exotic geology 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 top of that, each of the four giant planets has extensive systems of rings. Each of the rings is a prototype for the protoplanetary disk where all the planets formed.

Of course, protoplanetary disks happened a 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. 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. But 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. Yes, of course. You mentioned that even before the decadal survey process, you can look back more than 50 years and there were reports that talked about these kinds of goals for study of the outer planets. Apparently, we have quite a history of curiosity about these worlds. When I started talking about the Decadal Survey or writing about the Decadal Survey,

I wanted to be precise, so I started reading some older documents, and I started 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 questions really haven't changed since then. They are worded differently, but the three are about the origin of life and how life evolved. So that's one question. Another one is how the solar system formed and evolved. And the third question is usually worded in many different ways of it, but it is about present day processes, studying how the processes are working today and still making the solar system evolve. I'm struck by the last part of that last question that you posed in the magazine.

How do we get such diverse worlds? Because it would be wrong to think of these four planets as being terribly similar. these four planets as being terribly similar. I mean, they obviously share some similarities, but you see plenty of reason to identify them individually. Yeah, so we don't have to constrain ourselves to just the giant planets. I am a planetary atmospheric 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 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's parameters and 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 science is just like psychology. My wife is a psychologist, by the way. So I like saying that. In psychology, you do not understand one person to death to understand human mind and behavior, right? Yeah. So in studying planetary weather, we don't just study one planet to say that we understand weather. We study all the planets we can study and try to understand underlying laws of physics that governs the weather. 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've talked many times on this program about the surprises that wait for us and frequently the theories that have to be rethought. Yeah. My favorite example is the hexagon on Saturn. Of course, 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? Oh, many times, both with Linda Spilker, the project scientist for Cassini. Linda is still the person, the individual who's been on the program more than anybody.

And not that long ago with Carolyn Porco. Oh, great. My core specialty is atmospheric dynamics of the giant planets. So the hexagon on Saturn is one of my favorite features in planetary atmospheres. The hexagon was found in Voyager data. The spacecraft flew by Saturn in 1980 and 81. The hexagon in the data, of course, was not noticed until 1988, because it was in the polar region, and both of the probes, both of the Voyager probes flew by Saturn in the equatorial trajectory. So the hexagon was in the hard to find spot in those images. But in 1988, there was a paper that got published, and it was very

puzzling. It took a long time to really come up with an explanation. In 1991, there were some theory papers that proposed theoretical explanation for those things, for the hexagon. But it was difficult to prove. It was not until 2010 and after when the computer simulations 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 along the outline of the hexagon, there's a jet stream that's blowing eastward along the hexagonal outline. So we always knew that it was associated with the jet stream, but why it was meandering in the six-sided shape was something we couldn't really explain until the 2010s. I would bet then that you are just as fascinated by those six cyclones that have been imaged by Juno still actively orbiting Jupiter that are at Jupiter's south pole. In fact, there is a gorgeous, rather stunning image of these cyclones in your article in the Planetary Report.

Yeah, so it's definitely puzzling that those cyclones do not merge. This is a knowledge we have from Earth-Ocean 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 shock 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 Cheng Li. I think he just moved to Berkeley. He found a way to keep the cyclones from merging. He just presented the results at the AGU meeting last

December. And I think I've been waiting for that paper to come out. 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 missions that you're looking forward to in the next few years. And you identify several that you're pretty excited about, beginning with Europa Clipper. Sure.

So that is what has become of what was recommended by the last Dicalo survey. The last Dicalo survey's top three picks for large class missile. These are the missiles to be directed by NASA, managed directly by NASA. The top one is Mars sample return that became Mars 2020. The top one is Mars Sample Return. That became 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 Europa.

That is the Clipper missile that we are talking about now. And then, of course, the enormously exciting, not that Clipper isn't, but Dragonfly, which has really fired the imaginations of so many people, that mission that will be headed to Titan, although not for a few years yet. Yeah, it is part of the New Frontiers program. 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 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 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 asteroid. And then the fourth one is going to be Dragonfly.

I want to mention, at least in passing, the European Space Agency's current preparation for the JUICE mission, the Jupiter Icy Moon Explorer, another orbiter. I want to go further out in the solar system, too, and give some sympathy once again to poor 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? 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. I was in the second grade. I was attending school, primary school in Japan. When I started hearing the news on the radio and on TV about the Voyager 2 flyby of Uranus, I started asking a lot of questions to my parents about 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

that would be the japanese economy newspaper so it's a thick stack of paper right 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 finding it exciting, they just gave me a blank notebook and showed me how to cut out the article. And I actually still have that article. Oh, that's great. Yeah. So that was a really busy year for planetary science, because after the Voyager flybys, within a couple of months, the comet Halley flew by, came close to Earth, right? So there were a lot of articles back then

about the comet. So I really quickly filled up that first notebook and I still have it and it's one of my treasures. What a great introduction to planetary science. Now it's your profession. Would you like to see an orbiter out there at either Uranus or Neptune, or maybe both? Both, definitely. As an atmospheric scientist, I do not have a preference on Uranus or Neptune. I would 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.

What's interesting about all the other planets is that other than Uranus, all of them emit more heat than they receive from the sun. 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 gravitational energy is getting converted into thermal energy. And then the 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 could not see that for Uranus. That's the big mystery from the atmospheric sciences viewpoint, why Uranus 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 interesting place because of Triton. Triton is believed to be a captured 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, is believed to have formed in a similar way to Pluto. Studying any differences or similarities between Pluto and Triton will tell us more about how KBOs and far-out solar system objects may have formed and 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 ocean. Other people say that it's a sign that the solar heating causes surface evaporation

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. By flying by Triton and making close observations, we should be able to tell the source of energy that's powering those plumes on Triton. Besides, it's a spectacular landscape, and it would be nice to get some close-up shots of it to follow those 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 very promising moon. And you mentioned this in your article as well. Yeah. So two places we have a really good chance of finding present day life outside of Earth are Europa and Enceladus.

Europa, as you said, is the moon of Jupiter and Enceladus is the moon of Saturn. Both places are really exciting because they offer a subsurface ocean that are easy to access. Europa's ice thickness is expected to be maybe two kilometers in some spots that might allow some exchange of material between surface and the ocean. So if we land on the surface, we might be able to tell what might be in the ocean that's under the surface. And of course, Enceladus is really exciting because it's blowing up material from the subsurface ocean into space through the geysers near the South Pole. So if we can fly through the plume that's blowing out of the South Pole, we might be able to sample the ocean material without landing and see what might be in the

ocean. Well, let's hope that we get such intriguing data back from Europa Clipper that a Europa lander, if it's not already funded by then, that that will give plenty of encouragement to the people who control the wallets to make that mission happen. There's much more in the article that we could talk about. I'll just encourage people once again to go and read the digital version at planetary.org. Of course, Planetary Society members should by now have had the beautiful 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 giant gas worlds. And you've proposed a plan for doing just this. Can you tell us about

SNAP? Yes. SNAP stands for Small Next Generation Atmospheric Probe. It is a design that offers multi-probe missions to the outer planets. We have had two atmospheric probes that sent to the outer solar system. The first one was a Galileo probe that went into 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 measure that 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 future planet Uranus or Neptune, perhaps, 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 kilograms in mass. We do that by focusing on measurements that might return regional variations. It just so happens that measurements that are not expected to vary regionally, I guess, 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 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. There are a lot more condensables than just water on the outer planets. When we measure these quantities, we are basically measuring, making local weather measurements that might depend on the location. SNAP is going to offer a way to explore multiple locations on these planets in the future. You remind me that one of the problems with the Galileo probe is that it just had bad luck that, as we've talked about a couple of times on the show, it simply came down

in a spot that was not typical of a lot of the Jovian atmosphere. So you can see the real advantage of having a lot of these probes to drop into different locations. Right. Galileo probe really was a planetary hole-in-one. 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 already knew that there wasn't much water. Sort of a dry well.

That's right. That's how we are so excited about the measurement that the Juno team is about to publish. The results we are waiting to see from Juno. But it would be nice to have one in-situ confirmation to validate Juno's data. So that's one reason I said in my article why another probe to Jupiter will be valuable. So much more to learn. We have to hope that the scientific community, the planetary science community, and the Decadal Survey

will continue to push for these missions to the giant outer worlds of our solar system, and that we'll be able to come up with the wherewithal to get these missions funded and learn more about this still mysterious portion of our solar system. Cuneo, thank you for taking us on this little tour of the outer planets and the plans that you and others have to explore them further. I hope that we'll have more to talk about. And best of luck with everything that you're up to,

including a development of this concept called SNAP, the Small Next Generation Atmospheric Probe. Thank you. I enjoyed the interview as well. Planetary scientist Kunio Sayonagi. After a quick break, we'll wrap up our survey of the solar system with its smaller worlds and bodies. Hi, I'm Yale astronomer Deborah Fisher. 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 slash 100 Earths. Thanks. I saved our smallest but most numerous class of solar system objects for last, because they are everywhere. Maitreyi Bose is a 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.

My Trey, thank you so much for joining us on Planetary Radio to talk about, well, what's left in the solar system. After talking about everything else with your five colleagues who also wrote for the current issue of 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. It's a pleasure to be here. Yes, I did cover a few of them in the introduction of my article that are the more recent ones, I would say. But there has been in the past 10 years,

you know, a dozen visits, flybys, to several different asteroids. And we saw how they look, whether they have craters on their surfaces, whether the surfaces are smooth. So we learned quite a bit from several different flybys. What have we learned about the surfaces and the shapes of these asteroids thanks to these missions? the surfaces and the shapes of these asteroids thanks to these missions? The most recent one, I would say, was the JAXA mission to this asteroid Itokawa. We brought back samples from this particular asteroid, but we were also able to map and 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, meter, 10 meter

size boulders that are just loosely held together by gravity. That's pretty insane, right? I mean, you're looking at these asteroids, they should be these single little solid body, but they're not. When I was a kid growing up, all we saw were these big rocks in space that were obviously not piles of rubble. Right, right. And in fact, some of the asteroids, you know, a decent fraction of the asteroids are like that. So, you know, it's not just that every asteroid that we look at are rebel 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. What I should have said, of course, is that when I was a kid, we weren't seeing pictures of actual asteroids because there weren't any until some of these recent missions and some radar work, we should say. But in the artist's concepts, they were always these big rugged rocks. What about the shapes of these? I mean, 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 how these rubble piles come together and what they look like when they do? That's correct.

So Itukava, like I mentioned, is a rubble pile. The shape is this diamond shape. It looks like a top almost that's spinning. And that shape is very unique because two other asteroids that we are currently visiting, Bennu and Ryugu. Bennu is an asteroid that we will have samples from Bennu 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, which says something about the process by which they are made. which says something about the process by which they are made.

You mentioned something called the YORP effect, Y-O-R-P, which may have a lot to do with these shapes that we're seeing. What are we talking about here? What does that mean? Yes, you could imagine that you have a small body that is, light is getting scattered off the surface of this body, but it's also emitting some of its own thermal 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 stops that actually spin up or over time can spin down. And this spinning up and spinning down process can then lead to this top shape that we observe. And I wish we had more time to talk about this. We'll continue, of course, to talk about small bodies. And we'll continue to talk about Osiris Rex, which is still making those preparations to pick up that sample at Bennu, something that 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 has this other object now officially named Arrokoth. I hope I have that right. Arrokoth surprised some people, or at least it surprised me,

because it looked like some other things that we've seen around the solar system, notably some comets, like the one visited by Rosetta. Yeah, it's actually true. 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 contact binaries, which Arrokath 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 our planet.

I want to 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. Yeah, that's right. So 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. Because there is another school of thought that talks about these small bodies being just remaining material from the planetary formation process.

Now, if you look at very pristine meteorites, we see it does have ingredients that can make planets. So in meteorites, for example, you have chondrials, 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 formed from asteroids is true, then we can estimate how much water was then delivered or was present as collisions between asteroids formed these planets. So we're still following the water, at least as far as small bodies go. How do you conduct this research?

Do you work with the data from these missions? Not directly. So with the Hayabusa mission to Tokawa, they brought back samples and we have some of those samples in our lab. And I use laboratory techniques to measure volatiles in some of these tiny, tiny particles. I use this instrument called the nanoSIMS, which is a secondary ion mass 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 to give you an estimate of how small that is, diameter of human hair is typically 100 to 500 micron in size. So we have particles that are really tiny and we are trying to measure some of them in my lab. I am so impressed that with as small as that sample was, that was returned by Hayabusa, you must feel very fortunate that you were able to get even this tiny amount to put in your instruments.

Oh, yeah. It has been an amazing experience working with some of these samples because we have to devise new ways to even mount them. Right. We cannot. We get these loose particles. We have to find a way to not lose them because there is static electricity everywhere. So you have to have very specialized equipment which 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 lab equipment that can do nanoscale measurements. lab equipment that can do nanoscale measurements. Today, I'm putting your lab on my bucket list so that I can take a look at, even if it's under the microscope, at some of these tiny fragments from so far away. Because, you know, I've gotten

to see ALH 84001. I've seen pieces of the moon, but now I want to see some of Itokawa. I've seen pieces of the moon, but now I want to see some of Itakawa. Yeah, no, absolutely. I mean, once this pandemic is over, I would welcome you to my lab. In fact, there was supposed to be two visits, one of them from PBS Nova, which all has been delayed because of this pandemic that's happening. Whenever you're interested, just email me and I can show you some of the chakras that we have mounted very, very carefully and they are in the instrument right now. I'm going to 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? The obvious answer would, I guess, be yeah, from what we've seen so far. But 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 articles. Tell us about Lucy and why it's going to help to answer this question. Tell us about Lucy and why it's going to help to answer this question. Yeah, so Lucy, it's a NASA mission that will tour five Jupiter Trojans. And some of them are actually binary asteroids, which so, you know, with a total of seven 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, looked for clues as to if they're different or similar. That's the question. Are the Jupiter asteroids all been captured by Jupiter? Because Jupiter is so huge, right? It can capture it because of its gravity, which we think as a good, but we need to prove that. Before we move out really even to visitors from beyond our solar system, I want to see if you have any comment about one other mission that a lot of us are looking forward to. And that's Psyche, which is going to, for the first time, visit a kind of asteroid that nobody's been to before. kind of asteroid that nobody's been to before. Yes, so that's a very important animation close to my heart because it is being led by people at ASU from my school. Psyche is going to this

metal-rich asteroid. We think that there was this protoplanet. So, you know, before a planet forms, you have a smaller body that is just big enough to have an atmosphere of its own, can undergo differentiation like Earth has done. So it has a core mantle and a crust. So, you know, we think that there was this really large protoplanet 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 we're going to visit soon, which is pretty, yeah, pretty incredible that we can do that. Very exciting. I mean, who knows when we're going to,

if ever, possibly never, reach the core of a planet like Earth. 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. I'll 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 elsewhere, was discovered. And now we seem to be finding more a couple of years later, and we get Comet Borosov.

Tell us about this and why it's important to study them. 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 telescopes to, you know, map them or whatever. So right now we can do that very effectively, which, you know now we can do that very effectively, which 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,

the very specific angles through which they are supposed to come in. And we don't think that if it's a solar system body, they would have that path. That's like the easiest way to identify them. But somehow, you know, in our minds, we always thought of interstellar objects as 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, the Awamua Mua and Boriso, they both are different from each other, but they are similar in some sense to objects 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 solar system. Icy, has a tail, and so on and so forth. All of these objects, they're so unique, but they can say something about where they are coming from, you know, from which direction, maybe from which, you know, galaxy type. 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 up, like the Vera Rubin Observatory, we'll be able to identify more of

these and start classifying them and trying to then look for trends in how they look, which would be very, very cool, I think. I'm really looking forward to finding more of these first. Here, I'm talking about the difficulty of reaching the core of a planet like Earth. It is at least matched by the possibility of an interstellar mission to go out there and do in-situ examination of another star system. And yet here are these bits of other star systems coming right into our neighborhood. It's pretty exciting. Let me close with this, and I hope this isn't too far out of left field. We at least now have one visitor to the Kuiper Belt. Would you someday love to see something go out there much

further into the Oort cloud and take a look around there? Absolutely. I mean, I think, so what I'm going to say may not happen in my lifetime. But what I would really like to see is a small probe like a CubeSat that sits on one of these interstellar interlopers and takes us to where it came from. I think we should push for that. We know a little bit about CubeSats at the Planetary Society. So what a tremendous idea. I'm going to mention that to some of my colleagues. You should. No, I wish there were some way to do that. And I think the European Space Agency with its Comet Interceptor mission is going to get there,

because initially we just have to make sure that we find something and we go for it, right? Get as close to it as possible. But eventually, you know, if we can land on it and just be there sitting and let it take us wherever, that would be amazing. 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 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 tour of the solar system as we look toward the formation of the next Planetary Science Decadal Survey. I've really enjoyed talking to you, Maitreyi. Thank you, Matt. This has been amazing. Yeah, it's good to sort of

dream about things, right, and learn about our solar system and objects beyond, of course. But this has been a very, very nice conversation. Thank you. I think so, too. My conversation with Maitreyi Bose completes our whirlwind tour of the solar system. You can read the articles by all six of our scientist authors in the Planetary Report. You can read the articles by all six of our scientist authors in the Planetary Report. The 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 as we talk about the night sky, as big as that. 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? I'm finally healthier, I think. So that's a plus. Being at home, I don't mind being at home. I like home. Wait, here comes the dog. And there goes the dog. And that's one of the things you like, I know. And I do want to make it clear to folks that as far as we know, you were not caught by the COVID-19 virus. This was just something else. No, but I don't know. And I wasn't unhealthy enough to get tested considering the lack of testing around. So 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 mild in duration. And I'm sure that's what everyone tuned in to

hear. So there you go. Well, may everybody else who is afflicted with this have no worse an experience than you had. We certainly hope for that. And there's the dog hoping the same. You may remember that we talked not long ago about a certain popular delicious breakfast meat. Yes. This came from Mel Powell. He's suggesting this to you. Yes.

This came from Mel Powell. He's suggesting this to you. As seen from Earth, how many asteroids are within six degrees of asteroid bacon? Wow, I'll have to do a calculation. I'm guessing a lot. Now I'm going to actually, dang it, now I'm not going to get anything else done today. He did mention, you know, to let you off the hook, that, of course, they're always in motion relative to each other.

So, you know, you don't have to put too much time into this. What's up there other than asteroid bacon? There's asteroid sausage and asteroid eggs. No, no, no. There's actually a lot of stuff in the sky i i need to turn to serious sky guy for a second hey there matt there's good stuff i'm just that's way too serious i've lost my mind apparently it's the fever so in the pre-dawn east we've got jupiter mars and 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. 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 star cluster. So on April 3rd, it'll actually basically be crossing in front of the Pleiades. So a very nice view. Also, check out the cosmic balance. I don't know. The cosmic balance between where he is, Orion, which is in the south 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, at least kind of, you get to Venus, the brightest star-like object in the sky. Pretty groovy, huh? I love it. But wait, don't order yet. People may have been hearing there's a comet, Common 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 always with comets. We don't know how bright they're going to get. So it may get bright enough to see it with

the naked eye in mid to late May, or it may disintegrate as it heads closer to the sun. So we'll keep you posted. Keeping us guessing, that's what it's doing. As comets always do. We move on to this week in space history. It was 2001 that the appropriately named Mars Odyssey was launched. And amazingly, Mars Odyssey Orbiter is still working 19 years later. On to random space fact. Wow, I like that. 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, 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 meters away. How appropriate. Ola Fransen, one of our many Swedish listeners, he says, remember that astrophotography is the best social distancing. Universal distancing. Yeah, six light years is a pretty good, you're probably safe at six light

years. I think you're good. I think that's one thing that's actually certain. All right, we move on to the trivia contest. We discussed white dwarfs and the Chandra Sekhar 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 Chandra Sekhar limit? How'd we do? 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. And we had responses from, you name it, man, Australia, China, Siberia, the aforementioned Sweden from all over the place. It was Texas that our winner comes from this time. First time winner, though a perennial entrant, Paul Swan in Austin, Texas. He says that that Chandrasekhar limit is about 1.4 solar masses.

Is he correct? He is indeed correct. So if you get past that, depending on how much your white dwarf is rotating, then you go past the electron degeneracy pressure limit, and it squishes down into a neutron star, or if you get big enough, into a black hole. So yes, sorry, long answer of yes, that's right. Well, I'm so glad you mentioned those degenerate electrons because we have a poem from Dave Fairchild, our poet laureate 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 found. The point the collapsing star passes

is set on a scale above where it falls of 1.4 full solar masses. Wow, that was impressive. Hey, I didn't tell you yet that Paul is going to get a Planetary Society rubber asteroid. Had a little trouble getting the motor started. And a terrific book. I've been spending more time with this book. It's Spacefarers, How Humans Will Settle the Moon, Mars and Beyond by Christopher Wanjik, published by Harvard University Press. It's very entertaining. And 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, as down to earth as a book called Spacefarers can be. And he presents all the challenges as well.

It's very good. I recommend it. Here's some more stuff that we got from listeners. Another poem from Martin Hajoski. Setting the Limit is what this one's called. With apologies, Martin says to Dave Fairchild. Subramanian Chandrasekhar, Chandra for short, was only 20 when a special formula did he exhort. Though elders objected, young Chandra did retort, white dwarves maxes 1.4 solar masses.

The math did I sort. Gene Lewin, who often also sends us great poems, but he said, I'm amazed at the brilliant minds that can perform these astronomical feats. Isn't that incredible? I mean, we heard various ages, 19 or 20, for Chandrasekhar when he came up with this. And it wasn't very well received, but it turned out to be absolutely the way the universe works. Yeah. Devin O'Rourke in Colorado. Oh, only 0.4 more massive than our sun.

That's not so much. And then he realized there's still hundreds of times more mass than all the rest of the solar system combined. Crazy. Crazy. Bjorn Getta. Oh man, it's been, we don't get enough of these great special units that we sometimes hear from listeners. Bjorn Getta says that 1.4 solar masses, that's about 1.67 times 10 to the 30th coronas. That's bottles of corona, beer. A standard unit. Bob Lee in New York, based on his estimation of your mass, 3.4 times 10 to the 28th, Bruce Betts is. That is exactly right.

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 pro. I have heard all those names even strung together, but it's been a while. I looked it up. There actually is something to this. So thank you for that, Ashley. And Ashley gets the last word. We're ready for the next time. Down to something serious. What mission played the first musical instruments in space? Go to planetary.org slash radio contest. All right.

So you're talking now about more than just the beep, beep, beep of Sputnik 1? Yes. I'm talking about humans playing what would be standardly considered in some form musical instruments in their spacecraft while in space. So humans, not a recording. Not a recording. Humans. All right. We got it. And you've got until Wednesday, April 8th at 8 a.m. Pacific time to get us the answer to this one and because we are continuing our social distancing and headquarters for the planetary side is still closed down

I know, I'm disappointed too, dog It's another opportunity for you to win Bruce and or my voice, an outgoing message for your voicemail system, if you so choose. That's what we have for you as the big prize this time. But that's it for now. All right, everybody, go out there, look up in the night sky and think about

what degeneracy pressure you've overcome. Thank you and good night. Here's the pressure I've overcome. It's that great line from The Graduate. You are a degenerate. And the electron said, thank you. Thank you very much. That's Bruce Batts 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 because he joins us every week here on What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its members who want to explore our entire solar neighborhood. Join us by visiting planetary.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, at Astro.