Grounded: The director of the SOFIA flying observatory looks back

Mat Kaplan: The End of SOFIA, 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. SOFIA, the great infrared telescope mounted in a 747 aircraft, made its last flight on the night of September 30, 2022. Director of Science Mission Operations, Margaret Meixner, joins me for a conversation about the observatory's legacy, not long before she got on board for that swansong journey. You'll hear her sorrow and joy. It's a solid joy to know that the CD of The Moons Symphony is about to become available, including liner notes by yours truly. We'll have a copy for the winner of the new space trivia contest, Bruce will present today.

Mat Kaplan: Though I'm still feeling the symptoms, I'm very glad to announce that I've tested negative for Covid twice today. It has not been a fun 11 days of isolation, but my experience has been so much easier than many around the world. Still, it's partly why this week's show is a bit shorter than most. Be careful out there folks.

Mat Kaplan: A smashing success, that's how Nancy Chabot of the DART Mission described it in last week's show, and it's the headline for the September 30 edition of The Downlink, The Planetary Society's free weekly newsletter. Take a look at the spectacular image captured by Italy's little LICIACube, shortly after the impact. Wow. There's a link to many other images, and more about the mission, at planetary.org/downlink. Poor Artemis 1, NASA had to roll it back to the vehicle assembly building, ahead of Hurricane Ian. Now it seems the next launch attempt won't be till mid-November. That's also bad news for all the secondary payloads on board the space launch system rocket.

Mat Kaplan: Also in The Downlink is your chance to help give official names to 20 exoplanets, for real. This is through the International Astronomical Union, after all. Details on this opportunity are also in the Downlink.

Mat Kaplan: There isn't much I need to say ahead of my conversation with Margaret Meixner. It's always sad to lose a great instrument of science. This is worse, in at least one way than the collapse of the great Arecibo radio telescope, because this time it's intentional. But as we've heard many times from Planetary Society Chief Advocate, Casey Dreier, SOFIA, the Stratospheric Observatory for Infrared Astronomy, has long been under the eyes of NASA and others because of its expense. As you'll hear, Margaret is disappointed but accepts the decision to end operations. She notes that this leaves us with a big blind spot in our ability to understand the universe. You'll hear her mention the powerful interchangeable instruments that have enabled SOFIA to do its great work. They are EXES, from the University of California, Davis, FPI+, and FIFI-LS from the German SOFIA Institute, FORCASt from Cornell University, GREAT from the University of Cologne in Germany, and HAWC+ from NASA JPL.

Mat Kaplan: SOFIA itself is an 80/20 partnership between NASA and the German Space Agency, the DLR. You'll also hear Margaret mentioned IPAC, that's the Infrared Processing and Analysis Center at CalTech, where anyone can explore SOFIA's data. The science mission operations that Margaret heads are a partnership between the University's Space Research Association or USRA, and the German SOFIA Institute. It has always been based at NASA's Armstrong Flight Research Center in the Mojave Desert, not too far from Pasadena. And it was near there that I found Margaret preparing for the final flight.

Mat Kaplan: Margaret, welcome to Planetary Radio for a conversation about SOFIA, that flying observatory which has given me a couple of the best experiences I've had in my professional life. Thank you so much for joining us.

Margaret Meixner: Well, thank you Mat.

Mat Kaplan: We would've continued to report on SOFIA's wonderful work if it had a long life ahead of it, but of course, as you know, the end of SOFIA's days as a flying observatory is almost upon us. In fact, by the time our audience hears that, it will have passed. Are you still looking at September 30th as the last observational flight?

Margaret Meixner: Actually, the last observational flight will be tonight, September 28th. And I'm so delighted I'll be on it.

Mat Kaplan: I don't blame you. Boy, that's got to be poignant, very special. I mean, there is so much to celebrate with this observatory, but you have to have very mixed emotions, I assume.

Margaret Meixner: Oh, absolutely. I mean, when I took this position a little over two years ago, we were set to revamp and greatly improve the science productivity of SOFIA, which we did. And we were super excited about its success and we were deflated with the outcome this year, due to the decadal survey and then NASA and DLR'S decision to conclude the SOFIA mission. It's a sad moment, because SOFIA's worked very hard throughout its life. But particularly this last two years, we really ramped up. We were at peak performance in terms of flights, in terms of science publications, in terms of science community engagement. I suppose if you have to end, you're ending on a high note, but still, we could, funding permitted of course, probably go on for another decade. It's a tough decision that NASA had to make in light of the decadal, and we accept that. But personally, I'm very sad about the moment.

Mat Kaplan: We can get through the sadder portion of the conversation and move on to the happy stuff little bit later, because the observatory, SOFIA, has been so productive and has made such huge contributions, which I hope you'll be able to talk about a little bit. I've heard from some of your colleagues at the German Aerospace Center, the DLR, particularly the German SOFIA Institute, they are, I guess it's safe to say, not just sad, but probably a little bit angry. They would love to see this continue and in fact, they also have some hope that we're not going to see the last flight of SOFIA tonight, as you and I speak. Does it look like there are any prospects in that area? And do you have anything to say to not just the folks in Germany, but the other international partners and astronomers around the world who've relied on SOFIA?

Margaret Meixner: Yes. No, I agree with the sentiment of it being sad and disappointing. To my knowledge, we will not be continuing under NASA and DLR. I suppose somebody else could pick it up, but I have no news on who that would be, or how it would be operated or who would be operating it. Certainly it would be a fabulous acquisition if somebody decided to latch onto it.

Mat Kaplan: What happens now, at least in the coming weeks and months, to the plane, the telescope, those marvelous instruments that it has used to collect all this great data, and maybe most importantly, the team?

Margaret Meixner: Right. Let me start off with the plane and the instruments. I mean, some of the instruments are owned by institutions, and of course they get returned to those institutions, like the GREAT instrument, the heterodyne receiver instrument that belongs to University of Cologne. Likewise, FIFI-LS belongs to the German university in Stuttgart. But some of the instruments are what we call facility instruments, that's at NASA's discretion about where they land. And I haven't heard yet of what those decisions are. I mean, you hear things about [inaudible 00:08:38] some will go to a museum, maybe some will be reused for other parts. So my understanding is if there's an active use for something, that's the first priority, is it can be actively reused. The EXES instrument, of course, will go back to the PI at University of California, Davis, for potential reuse. Then in terms of the airplane, again, that is government property. That and the telescope of course, is German government property. So those things are handled by NASA and DLR to figure out where those things are going.

Margaret Meixner: Now, about the team, that I can speak more directly for. We have a closeout plan that follows along what work the government needs from USArray Science Mission Operations, and we've hammered out that plan, which includes summary reprocessing of the data. SOFIA will live on in the Infrared Science Archive, located at IPAC. You can get some of that data now, but we will be reprocessing it to make the best archive for some sets of the later sets of the data. We have a one year time scale for that. And we have been working with our team to keep them informed throughout the process since April. We've been absolutely transparent about what we're trying to achieve and close out, including input from them as much as possible, and just going back and forth in terms of what's happening and giving them plenty of notice so they can seek out other positions.

Margaret Meixner: Now, the SOFIA team is amazing. It literally is the best team I've ever had the pleasure to lead. They're incredibly dedicated, they're very smart, they're very resourceful, and they're very team-oriented. And if you've ever been on a flight and you have at least five different parties having to work in unison to execute the observations and they do it flawlessly. I mean, this year it's been flawless operations, and some of them... SOFIA is a mix of people who love astronomy and also love aircraft, and so you can imagine that where they may go depending on what their desires are. And we are giving them every support we can in terms of trying to identify other opportunities that might interest them. I can tell you, if you're out there reviewing any of their resumes, they're amazing and you'd be lucky to have them on your staff.

Mat Kaplan: I have to think that listing this experience on their resumes or CVs has got to be pretty attractive to wherever they may end up next. I have personal experience of how the different elements of this team work together, from that flight that I and a couple of my colleagues made in 2015, and how well it was managed, how well it was put together. It was just truly, as I already said, one of the great experiences of my professional, really my entire life, to see how they work together from the cockpit back to the telescope itself to deliver the science that SOFIA was capable of. It was very, very impressive.

Margaret Meixner: Yes, it is.

Mat Kaplan: Are we going to be seeing good science come out of SOFIA data for a long time to come?

Margaret Meixner: Oh yes, most certainly. I mean, the last flight is tonight. The HAWC+ instrument's on the flight. It's been one of our most groundbreaking instruments, because it's able to measure magnetic fields in nearby star forming regions, as well as nearby galaxies. We have not only the individual investigative programs, but we have a number of legacy programs where PIs get a larger chunk of time. They do a very comprehensive survey, and that data goes into the archive, available immediately for anybody to use. But then they also work on maybe some higher level data products that they can deliver back to the archive, and analysis tools. All those things, we hope really enrich the archive. The archive is going to be available for the foreseeable future. It's at one of NASA's Infrared Science Archive, and I'm expecting to see SOFIA papers 20 years from now, because someone goes back, looks at something, analyzes it and comes up with a new discovery.

Margaret Meixner: We do have some science events coming out. We have something on Active Galactic Nuclei signatures for eight Active Galactic Nuclei, and that will be active in October. That is in our discussion. All of our science presentations and many workshops, talk about SOFIA data, but they talk about the multi-wavelength nature of astronomy, and how it's used with in conjunction with other observatory's optical and UV and x-ray and radio.

Margaret Meixner: And of course the niche that SOFIA's providing is this wavelength range in the far infrared where most of the radiation from cosmic ecosystems come out. And so it is a very key area of diagnostics and I'm excited about that workshop. And we have a number of other workshops that have happened over the past two years in this very important effort we've had with science outreach and communication to show people what SOFIA data can do for them.

Mat Kaplan: Margaret, do you have any idea how many papers have been published that have been based on, at least in part, SOFIA data?

Margaret Meixner: Indeed, I do. I'm going to give you a round number around 300.

Mat Kaplan: Wow, that's impressive.

Margaret Meixner: So we really started taking lots of science seed in 2014.

Mat Kaplan: I hate to ask scientists, leaders of projects this question, but you probably expect it. I wonder if there are any greatest hits that you'd like to call attention to. I don't want to offend anybody who isn't included, but maybe just a selection of results that indicate the breadth, the spectrum of work that SOFIA has been able to achieve.

Margaret Meixner: Sure. I've been rehearsing a lot of that this past year because we've been putting together senior review reports and bulletins and stuff. I'll hit a few of them for... Maybe I'll hit one for each instrument.

Margaret Meixner: For FORCASt, probably the best known result worldwide is the water on the sunlit surface of the moon that came out in... I think it was October 2020, and super exciting result. There was known to be water in the polar ice caps where it was cold, but looking at the sunlit surface was sort of a bold move. And the team that did that, it was very impressive, exciting. And we actually awarded them a legacy program to map water at different samples across the whole surface of the moon to better understand this. And we finished most of it, but not all of it, a couple weeks ago when we finished the FORCASt series. And super exciting and I think another paper came out showing a result of that and showing how it changes.

Mat Kaplan: Before you go on, I just want to say that that result caused a lot of excitement among my colleagues at The Planetary Society. The fact that there might be-

Margaret Meixner: Oh, I bet.

Mat Kaplan: ...water locked up right out there in the bright sun on the moon, at least during the daytime, pretty exciting result.

Margaret Meixner: It's very exciting. Not clear what it means, and that's what the legacy program is hopefully going to elucidate. And again, because it's a legacy program, that data goes immediately to the archive and the team is going to make a better improved... I think they have plans for making an improved archive of their traces of water on the sunlit surface.

Margaret Meixner: Let me pick the great instrument, this is the German instrument, the Heterodyne receiver. It's had a number of fabulous results, but one that really stands out is the first ever detection of helium hydride. The wavelength range SOFIA covers uniquely covers hydrides. Their strongest transitions are in the far infrared, so it's the ideal wavelength to look for them. And helium hydride is a molecule that thought to be key very early in the universe, because of course the universe started off as hydrogen and helium and then we build from there. And helium hydride was thought to be the first molecule. They found it in a planetary nebula, just the right conditions that they could detect it. And that was very exciting first because it gives you insight into the chemical reaction rates that create it. And that helps put constraints on theoretical modeling of what happens early on in the universe. So that was a big impact, the great deed.

Mat Kaplan: I just want to make the comment now about what this indicates about the hole that SOFIA has filled, which I've heard about from several other scientists, that the lack of SOFIA is going to leave us without a lot of ability to examine some of these wavelengths, isn't it?

Margaret Meixner: It is. One of the reasons I became director is, I thought this SOFIA is the only working Far Infrared observatory in the world at the moment. And it's important to make it as scientifically productive as possible. And like I said, I believe we did that. But when it goes away, when it takes it's last flight tonight, the astronomy community won't have an observatory to apply to with projects in mind. The fortunate thing is the decadal recommended that NASA invest in this wavelength range with potentially a probe, it might be an x-ray or far infrared probe, and on next generation great observatory down the road.

Margaret Meixner: So it is realized to be important in that process, but we will have a time gap for sure. We will have a time gap.

Mat Kaplan: It just occurred to me that there may be people thinking out there, well, the JWST, the James Webb Space Telescope, that's an infrared telescope, but it's not designed for the far infrared, is it?

Margaret Meixner: That's correct. I mean James Webb finishes at the wavelength of around 28 microns and SOFIA covers 5 to 600 microns. And as I mentioned, the bulk of the radiation from cosmic ecosystem comes out in the far infrared ranging from 28 to 500 microns. It's directly probing the interstellar medium. And when you look at spectral energy distributions of galaxies, there's two bumps. There's the optical UV, which is where the stars are coming out. And then there's the far infrared, the mid to far infrared because that's where the interstellar medium is radiating a lot of its bulk radiation because of dust. Dust absorbs the stellar radiation and re-emits it in the infrared.

Mat Kaplan: I interrupted your greatest hits there, so please.

Margaret Meixner: Oh, right. Yes, greatest hits. HAWC+ is the newest instrument and I can tell you, in the most recent cycle it was the most popular instrument to apply for. And it does something revolutionary. You can do photometry at the far infrared. But what it has added that we didn't have with other observatory like Herschel was a polarimeter to measure magnetic fields. Astronomy is very data driven and you need data to guide the field. Magnetic fields are always thought, well, they're important, but because you don't have data on them, you don't really know how important they are, you don't really know what their contributions are.

Margaret Meixner: And HAWC+ really has revolutionized that because people could apply for and start to study the magnetic fields straight by the dust. And again, because the far infrared covers that peak of the spectral energy distribution, it's a very sensitive wavelength to match these magnetic field measurements and you can peer all the way down to where the star is actually forming.

Margaret Meixner: One of the cool results that came out was on the Serpens cloud where they show how the direction of the magnetic field changes with the column density and extinction. The plank mission showed us that really far away from dense clouds, the interstellar medium kind of follows along the lines of the magnetic field. There's this wispiness, but then you get down to becomes denser. The magnetic field is perpendicular to the structure, you see the filament and it sort of looks like it maybe prevents it from collapsing into stars.

Margaret Meixner: But then when you get to super high densities and this needed the angular resolution that HAWC+ offered as well as the sensitivity to look deep into the cloud. You find at really high extinctions or column densities, that magnetic field reorients itself and actually helps feed the gas to form the stars and the clusters.

Margaret Meixner: That was really exciting. People may have predicted it, but here you have the HAWC+ evidence showing what is happening. And we commissioned two legacy programs, one's by Thushara Pillai who's doing something called SIMPLIFI and Ian Stephen's doing something called field map where they're actually mapping these filaments in the magnetic fields. And so that's a super exciting result.

Margaret Meixner: Let's see. Going on to FIFI-LS, for me, I love the Magellanic clouds and we started what we called a Pilot Legacy Program where they're mapping a large portion of the south molecular range and it's the first time. That's one thing that we're going to miss, with SOFIA it's very efficient at mapping large regions with spectral lines compared to the prior observatories. And it just has mapped a really large region and C+. And the C+ line, the carbon line, it's one of the brightest lines that you can see in the universe. It contain about a 2% of the galaxy radiation because it's a dominant cooling line of the interstellar medium, super bright.

Margaret Meixner: Again, nearby universe, you can only see this in the far infrared. And so SOFIA has done a lot of work with FIFI-LS and GREAT to map out and understand the context of this key cooling line. People use the ALMA telescopes, measure it at high redshift because it's really bright, you can see it. But with the SOFIA, you can actually understand where it comes from. Does it trace star formation? How does it trace the column density of gas? There's a lot of utilities. It's a workhorse line in the far infrared wavelength range. And so we'll miss seeing that for a bit.

Margaret Meixner: EXES. EXES is a very high spectral resolution in the mid infrared. It covers the same wavelength range as JWST MIRI, but extremely high spectral resolution. You can really pull out all the lines. And there's been a lot of remarkable work done on water lines at other sort of prebiotic molecules around forming stars where they've been able to measure the content of prebiotics, like settling and things like that and water, interior and discs where planets are forming around massive stars. And then being able to divulge that and do spectral line surveys has been, I think a really landmark area for SOFIA. So I think I've covered all the instruments with something each. I think they're all spectacular and special. I'm sad to see that we won't get to use them anymore after today.

Mat Kaplan: Certainly presents a lot of evidence and just a fraction of what SOFIA has been able to accomplish, that tells us about the value of this observatory there. There's something else that I'm thinking of that has been of value, I think, and I saw evidence of this on the flight that I made with my colleagues in 2015. We weren't the only people along for the ride. There were I believe three teachers. I think they were high school science teachers who were participating on behalf of their classes back at their schools. It was kind of the culmination of a long line of study that they had been conducting. Talk a little bit about this program and how it represents the outreach that you've been able to accomplish through SOFIA.

Margaret Meixner: Right. Well I have to say that that's done by another organization with SOFIA, but I have certainly witnessed it like you did. Very valuable type of outreach, unique in the realm of NASA because we can't send teachers up to touch Hubble. It's a robotic mission for often space. And only if you're a highly trained astronaut can you go repair it. But with SOFIA, we land every day and take off every day. And that enables us not only to fix and repair instruments and stuff, but it allows us to take new people on. And the teacher program is phenomenal, phenomenal.

Margaret Meixner: I had teachers come up to me at the [inaudible 00:26:00] saying, "We are so sad that SOFIA's going away because it was such a inspirational opportunity." And these teachers do come on board, they've done some prep work, they teach their classes about it. It really pulls in through the teachers the excitement of doing science, of working in STEM. It's a very exciting opportunity and I loved talking to the teachers that have been on board.

Mat Kaplan: As I said, I saw direct evidence of this as well. And just in the enthusiasm of these teachers, they obviously felt as fortunate as we did to be on board SOFIA for that flight. You said you're going to be on that flight tonight, the last flight as far as we know with SOFIA conducting observations, what will be the target this evening?

Margaret Meixner: Oh right. Well I can tell you when we do a flight series, we always do the most important targets first. So just to tell you about the flight series of this HAWC+ run, the primary target which had already been accomplished, that was to finish the mapping of the magnetic field in the galactic center. That was super exciting.

Margaret Meixner: On this last flight, we continue to map magnetic fields in different objects. We are looking at these legacy program, two legacy programs. One is the one I mentioned with the filaments. We're looking at two filaments from the SIMPLIFI program where we're mapping the magnetic fields in a star formation, star forming filament.

Margaret Meixner: And the other one is for a galaxy. It's a Starburst Galaxy NGC 253. And that's for another legacy program called SALSA, led by Enrique Lopez Rodriguez. And he is mapping the magnetic fields in a number of iconic nearby galaxies and just showing a whole new light as to what's happening in these galaxies. So, that's what's happening. We're mapping magnetic fields in the universe tonight.

Mat Kaplan: Margaret, clear skies tonight. On that last flight of SOFIA, please convey a message from Bill Nye and all of us at The Planetary Society and probably everybody listening to this as well, thanking and congratulating everybody on board and everybody on the ground who has contributed to all of these successes that you've given us a taste of with SOFIA and best of continued success to all of you as we watch the data continue to flow.

Margaret Meixner: Thank you. Thank you so much, Matt. And we really appreciate all the fan support The Planetary Society had for us over the years. Keep your eyes open for SOFIA results, they will still continue to come out and they will still continue to inspire.

Mat Kaplan: Margaret Meixner is Director of Science Mission operations for SOFIA. I'll be right back with Bruce. First though, an encore visit with John de Lancie, the actor many of as Star Trek's Q.

John de Lancie: Star Trek has always represented the hope for a better future. I don't think you can have that without pushing boundaries. And in the case of space, that is all that we're doing, is pushing those boundaries and finding out more, always finding out more. And I think it's really important as a human being, as a society to be able to do something like that. And this is where we do it. 200-300 years ago, we did it on sailing ships across the ocean.

John de Lancie: Space is important to me because it's kind of a metaphor for risk taking, tremendous rewards, possible rewards, being more expansive in one's thinking and opening oneself up to the infinite possibilities.

John de Lancie: Probably the biggest thing that differentiates Star Trek from almost everything else is the community in which you enter. Well, The Planetary society is that type of a community. If you share like me, the need to expand into infinite possibilities as my character does in Star Trek, and as I have said to Picard on more than one occasion, then certainly joining The Planetary Society is a good way to go. Join The Planetary Society.

Mat Kaplan: Time for what's up on Planetary Radio. And I'm joined therefore by the Chief Scientist of The Planetary Society. Right now it's Bruce Betts. I mean it's always Bruce Betts, he's always the Chief Scientist. I don't know what I meant by right now. Back in 2015, he was still the Chief Scientist.

Bruce Betts: I was still Bruce Betts. Hi, Matt. And what'd we do in 2015?

Mat Kaplan: We went with our good friend Merc Boyan, our video guy from The Planetary Society, our ace video guy. And we wrote on that plane just as I mentioned during the interview with Margaret a few minutes ago. Man, it was a great experience. You and Merc tried to get in some sleep. I was just too popped up to sleep. I just enjoyed being there the whole time. It was great.

Bruce Betts: I don't remember trying to get in sleep. We filmed some random space fact videos, did you think we were sleeping?

Mat Kaplan: Now who was that in the seat then? No, I think you tried toward the end of the flight. I mean, watch all night so it's understand-

Bruce Betts: Oh right, when we were headed back at dawn.

Mat Kaplan: And we're going to link to those random space fact videos. There's another video that Merc made just generally about the experience. And then of course the show, The Planetary Radio episode that came out of that experience as well. What a great adventure.

Bruce Betts: It was. And a very, very impressive facility.

Mat Kaplan: So if you were up there above the clouds with a big telescope, what would you be looking at though right now?

Bruce Betts: Well, being a planetary guy, I would look at planets. And I would look in the evening and I would check out over in the east, moving towards the south, at least for those of us in the northern hemisphere, bright super, very bright Jupiter hanging out in the sky and to its upper even right, Saturn. Moving the sky towards the west and you'll see a yellowish object that's Saturn. You have any trouble finding these, which you shouldn't for Jupiter because it's brighter than the brightest star. The moon is hanging out between them or near them, moving from Saturn on the 5th of October to Jupiter on the 8th of October.

Bruce Betts: Coming up couple hours later in the mid evening, mid to late evening, is Mars looking very bright. Mars brightening for the next couple months. You can watch it over the next two months, brighten by about a factor of three. But it's already very, very bright as earth and Mars approach each other in their orbits as they do every 26 months. If you have a good view to the eastern horizon or up before dawn for some reason, like you had an 80 pound dog jump on top of you, not that that ever happens to me, but it does. You can check out Mercury, but very low to the horizon, gets about its highest on the eighth and then heads back down, being that sneaky little bugger that it is.

Mat Kaplan: For 20 years now, I've thought about the astronomers out there who say, "Why isn't he giving us right ascension and declination instead of upper Right?" Well, because not many people know what those are.

Bruce Betts: Yeah. My general philosophy, right or wrong, as you've probably noticed, is easy things to look for, described in an easy, albeit somewhat vague way. And since I only tend to talk about bright objects, you don't need the RA and Dec as we say in the know. Basically right ascension and declination for those who don't know are sky coordinates that astronomers use. It's like latitude and longitude on the earth to identify where you're looking in the sky.

Mat Kaplan: Thank you. I should have asked you that probably in the first year of the show, but better late than never.

Bruce Betts: Well keep thinking of these questions for the next few weeks, we'll address them.

Mat Kaplan: Will do.

Bruce Betts: Meantime, let us move on to this weekend's space history. I remember 1967... Apollo 7, the first crewed Apollo mission to space flew, launched this week in 1968.

Mat Kaplan: Crewed as in people on it, not because it was a crewed version of Apollo?

Bruce Betts: They got into a little trouble, but that wasn't necessarily for being crewed, just... Anyway, that's a whole another story. But I will throw in a bonus random space fact before we get to the real one because I've used it before, which is Wally Schirra, who is the commander of that mission, is the only astronaut to fly in Mercury, Gemini and Apollo.

Mat Kaplan: Love it. He was a fun guy too.

Bruce Betts: Fun guy. Not to be confused with the mushroom. Undo, spider, spider.

Mat Kaplan: Ooh, if only people could see your mouth working as you did.

Bruce Betts: Anyway, Matt, you may have wondered, how heavy is that telescope that they carry in an airplane?

Mat Kaplan: I have.

Bruce Betts: Well, the installation weight of these SOFIA Airborne Observatory of Telescope was the equivalent of more than a dozen DeLorean cars. I decided to put in something everyone has an intuitive feel for.

Mat Kaplan: Yeah, sure. That's great. Did they include the time machine portions? What was it called? I forget what the device was called, we'll get it.

Bruce Betts: The flux capacitor.

Mat Kaplan: That's it. Of course, the flux capacitor.

Bruce Betts: Yeah, this doesn't count when they're like time displacement. This is just your standard run of the mill DeLorean, I guess. No, DeLorean is standard run of the mill.

Mat Kaplan: And no Mr. Fusion built into the hood.

Bruce Betts: No, they knock on to the future. Anyway, it's about 17 tons for those of you who don't have a good feel for DeLorean, but do have for some reason, a good feel for what 17 tons really means. Really impressively heavy flying in an airplane.

Mat Kaplan: Trying to come up with a good rhyme. 17 tons and what do you get? A telescope that flies inside of a jet. There, I did it there.

Bruce Betts: There it is. Wow, we witnessed it in real time. Nice. Wow, that stands alone. I'm moving on to the trivia contest. I asked you what is the approximate diameter of the crater that Deep Impact made when it impacted comet Tempel 1? How did we do Matt?

Mat Kaplan: Really well. It was great to hear from everybody, still getting those great messages from everybody about my plans. Thank you for that everyone. I am so far behind in responding, but it is my plan, my intent to respond to everybody who had something nice to say. One of those nice things said came from Gene Lewin from Washington. He also sent this poem, "When all the dust had settled, Tempel 1 one had a big dent. A crater now existed from an impact we had sent. It left quite a divot, 150 meters wide and opened up this comment so we could see what was inside."

Bruce Betts: Oh, very nice. Divot?

Mat Kaplan: 150 meters.

Bruce Betts: 150 meters as determined from later spacecraft fly by of the Stardust Follow-on Mission.

Mat Kaplan: Yeah, which we've heard from a whole bunch of people because you did mention that it was Stardust repurposed his NExT. Which is pretty amazing, that they were able to take a spacecraft that flew through the tail of a comet and repurposed it to take a quick look at-

Bruce Betts: It's amazing. I do have to correct you on a incredible subtlety. It did not fly through the tail, it flew through the coma.

Mat Kaplan: Ah, thank you very much. Yeah, so much closer actually to the body of the Comet.

Mat Kaplan: We have a winner, Daniel Huckabee. He is a past winner, but it has been well over three years since Daniel Huckabee in Nevada picked up a win here. "Here's a greetings Matt and Bruce. Interesting tidbit, Diameter of the crater left by Deep Impact a little bit larger than the height of the great pyramid of Giza, which is 430 feet tall." He says, "PS: We're going to miss you, Matt." Thank you Daniel. I'm going to miss you too.

Mat Kaplan: But Daniel, you get this prize to help you stop worrying about that. It's the medallion that The Planetary Society created in 1989 to commemorate the void your missions, Neptune and [inaudible 00:38:59]. We will [inaudible 00:39:00] one of those in the mail to you in the afternoon. Daniel and... Oh, who wants one there? Which of the dogs wants a medallion?

Bruce Betts: That's Gracie. Gracie desperately wants medallion, she loves them. Well, they're dog treats, right? Medallion brand dog treats.

Mat Kaplan: No, I'm afraid not. They-

Bruce Betts: Oh, sorry. Nevermind, they're not dog treats. Yeah, she's quiet now.

Mat Kaplan: I got more. Mel Powell, funny guy in California. He tried to get Rae Paoletta, our colleague Rae, to tell him on Twitter how tall you and I are. And then he was going to lay the two of us and some clones in the crater to say how big the crater was across. But she didn't answer. So anyway, he may amend his answer.

Bruce Betts: I'm not sure that's part of the official information she has, but I'm taller. That's all it matters.

Mat Kaplan: Quite a bit. Set upon [inaudible 00:39:54] in New York. He said it's approximately 1 trillion of Earth's aphelion. 152,100,000 kilometers 450 meters, that's the 1 trillion. Aphelion? Help us out here.

Bruce Betts: Wow. That is a really obscure, wonderful unit. Not aphelion so much, but comparing it to the size of a crater, very impressive I guess. Aphelion is an elliptical orbit as they are. Aphelion is the farthest point from the sun and Perihelion is the closest point to the sun. Earth is mostly circular, but it is not completely circular. So, it has aphelion and perihelion.

Mat Kaplan: Thank you. Chris Mills, Maybe they should have named that Copper Impactor, the one that deep impact slammed into the comet. Maybe they should have named it Matt, because I have made... He says, " a deep impact."

Bruce Betts: Wow. Okay, I've kind of vaporized, but-

Mat Kaplan: Thank you Chris. And finally from our poet Laureate, Dave Fairchild in Kansas, "Comet Tempel got a smack and found it had a crater. It was size 500 feet, we found out somewhat later. NASA Stardust took a pic, which helps us to deduce it's just about the same as 85 to 90 Bruce."

Bruce Betts: Yeah. No, that works. I mean, I'm 1.8 meters, something like that. Six feet tall in the morning.

Mat Kaplan: Well, thank you Dave. Thank you everybody. We're ready to go on and boy, we have a great prize.

Bruce Betts: Okay, well, I've got a great question. Name the solar system body and the category of geologic feature that are officially named after abandoned cities. So we're looking for a planetary body, like a planet asteroid and a category of geologic features like mountain. But we're looking for the proper Latin term and we're looking for ones that are officially named after abandoned cities. Go to planetary.org/radiocontest.

Mat Kaplan: Wow. I hope one of these features is Turpan, an abandoned city on the silk route that I actually went to once many years ago. But that's another story. You have until the 12th of October. Wednesday, October 12th at 8:00 AM Pacific time to get us this answer. And here's the prize, The Moons Symphony by composer Amanda Lee Falkenberg. And conducted of course by Marin Alsop. It is absolutely gorgeous. The BBC has just come out with an article praising it in its classical music magazine. It's from Sigmun Classics. I highly recommend. It's seven movements each inspired by a different moon of our solar system. And boy did I have a good time watching it being recorded by the London Symphony Orchestra under the baton of Marin Alsop. I think we're done.

Bruce Betts: Wow. Very cool. Thank you for listening. And everybody go out there and look up in the night sky and think about what Matt's head looks like when it... No, think about Matt... No. Hey, just think about Matt. Thank you and goodnight.

Mat Kaplan: Okay. That's enough. You can stop now. He's Bruce Betts, the Chief Scientist of The Planetary Society who joins us thoughtfully every week here on our show.

Mat Kaplan: Planetary Radio is produced by The Planetary Society in Pasadena, California. And it's made possible by its members who never want to see the end of our quest. Help them help science and space exploration at planetary.org/join.

Mat Kaplan: Mark Hilverda and Rae Paoletta, our Associate Producers. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. Ad astra.