Planetary Radio • Jul 08, 2020

To Pluto and Beyond with Alan Stern

On This Episode

Alan stern

Alan Stern

New Horizons Principal Investigator for Johns Hopkins University Applied Physics Laboratory

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Planetary Radio Host and Producer for The Planetary Society

It has been 5 years since the New Horizons probe revealed beautiful, surprising Pluto, and 18 months since it showed us the odd little body now known as Arrokoth. Principal Investigator Alan Stern shares the latest science, and tells us what the spacecraft is up to now as it races toward the edge of our solar system. Have you seen the new comet? Bruce Betts tells you where and how to look in this week’s What’s Up.

Color and composition of Arrokoth
Color and composition of Arrokoth The uniform color and composition of Arrokoth’s surface shows the Kuiper Belt object formed from a small, uniform, cloud of material in the solar nebula, rather than a mishmash of matter from more separated parts of the nebula. The former supports the idea that Arrokoth formed in a local collapse of a cloud in the solar nebula. NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute / Roman Tkachenko
Mat Kaplan and Alan Stern at JHAPL
Mat Kaplan and Alan Stern at JHAPL Mat Kaplan and Alan Stern at the John Hopkins Applied Physics Lab on December 30th, 2018, shortly before the New Horizons Arrokoth encounter. Mat Kaplan

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Mat Kaplan: To Pluto and beyond. Checking in with Alan Stern of the New Horizons mission this week on Planetary Radio. Welcome, I'm Matt Kaplan of the Planetary Society, with more of the human adventurer across our solar system and beyond. We welcome back one of our most frequent guests as the New Horizons principal investigator helps us celebrate the fifth anniversary of his spacecraft's Pluto encounter. Wait till you hear what it has been up to since. Alan will also share plans to ride along as Virgin Galactic and Blue Origin carry science to the edge of space.

Mat Kaplan: Have you seen the comet? Bruce Betts will tell you how when we reach for the sky in this week's What's Up segment. Ever been in a dust storm? I have, but it wasn't on Mars. The European Space Agency's Mars Express orbiter captured a truly jaw dropping image of a line of dust clouds rolling across the red planet's surface. That's the first thing you'll see in the July 3rd edition of The Downlink at

Mat Kaplan: Then there are the headlines collected by our editorial director Jason Davis, including the delay in the launch date for Perseverance. NASA's Mars 2020 rover will now liftoff no sooner than the 30th of July. It's the upper stage of the Atlas V rocket that is causing worries not the rover. NASA is joining with the Royal Australian Air Force, and the newly created US Space Force to find and track potentially dangerous NEOs, or Near-Earth Objects. They'll use a telescope that is being moved from the US to down under for this work.

Mat Kaplan: NASA also blew up its giant Space Launch System rocket. Don't worry they did it on purpose by filling the liquid oxygen tank with water and subjecting it to far more pressure than is ever expected on a mission. You can check out the visits some of my colleagues made to the SLS test stand back in 2016. This link and so many others are at We'll mail it to you every week for free if you'd like.

Mat Kaplan: July 14th 2015. I didn't get to join Allen Stern and his team at the Johns Hopkins University Applied Physics Lab for the climax of the New Horizons mission. We now know that the Pluto encounter was only the first climax for this spacecraft that left Earth in the first days of 2006. It went on from revealing the beauty of Pluto to an oddly shaped object called Arrokoth, and now is doing groundbreaking science as it plunges toward the edge of our solar neighborhood. It is even reaching out to nearby stars.

Mat Kaplan: Alan has more credits and accomplishments than we have time to read, but they include his service as NASA's associate administrator in charge of science. He has a hand in many projects and missions, and is associate vice president and special assistant to the president at the Southwest Research Institute. He joined me a few days ago from his home in Colorado, to celebrate the fifth anniversary of the Pluto flyby and much more. Alan, welcome back to Planetary Radio, you have been on as much as just about anybody, and it is always a great pleasure and an honor.

Alan Stern: Well Matt, thanks for having me back. It's an honor at my end too.

Mat Kaplan: I'm glad to hear that. This interview is going to be made available to our listeners very, very close to the fifth anniversary of that glorious day when your spacecraft had its thrilling closest encounter with Pluto. And now, it's been just what? About a year and a half since its second big triumph the flyby of what we now call Arrokoth. 14 and a half years in space and you're still not done. Where is New Horizons now, and what shape is it in?

Alan Stern: Well, New Horizons is one amazing bird. It's really a testament I think to American workmanship. New Horizons is now, if you can believe it, more than five astronomical units, that being the distance from the Earth, the Sun five times that far from Arrokoth already, or over two billion miles past Pluto, we are 47 times as far from the Sun as the Earth is. Next year in early 21 we will cross the 50 AU marker, astronomical unit marker. And, I think we're going to have some a celebration not many spacecraft have been this way before.

Mat Kaplan: No. You'll be what? Number five, I think.

Alan Stern: Number five or number 10, depending if you count the derelict upper stages for each of the five.

Mat Kaplan: Yeah. Okay. Well, the ones that actually talked to us for a good part of that mission.

Alan Stern: Right. Well, the spacecraft is in perfect health. We're not using any of the backup systems because of failures. And, we've got fuel to run this thing and power to run it, possibly for as much as 20 more years, so I'm excited about the science that's still ahead.

Mat Kaplan: We're going to talk about the science that is just past, the most recent announcements that you've made, and what may be ahead as well. But, I want to ask you, first of all, looking back at the amazing ongoing success of this mission, it's hard for me to believe that it took so much blood sweat and tears to get it funded and underway. You document those challenging years and your book Chasing New Horizons that you and David Grinspoon, your co-author came on the show a while back to talk about. In those difficult times did you ever come close to giving it up, and just saying the hell with it?

Alan Stern: It was really tough, and for the readers who don't know the story, it felt sometimes like being trapped in maze from 1989 to really about 2003 or 2004 when it was clear the mission will be fully funded. Because NASA studied a lot of different ways to go to Pluto, and one after the other got canceled until we got New Horizons. It took a lot of stamina, and a lot of persistence, but I don't ever remember thinking we should quit.

Mat Kaplan: I'm not surprised. You just don't seem like that kind of person. And, and thank God because look at what's been accomplished.

Alan Stern: And, all spaceflight is what I call a team sport. No spaceflight is ever done by one person. To sell this mission ultimately took the first Planetary Decadal Survey recommending it as the number one priority of that Decadal Survey. So, a lot of people were involved in that, a lot of people were on the other teams that competed with New Horizons for the chance to be NASA's Pluto mission. And then, New Horizons was a pretty large project in the early days. When we were building it, we estimate that about 2500 men and women were involved in one part of it or another. So, a lot of people to make this thing come together.

Mat Kaplan: And, you didn't have much time, did you? I mean, at least not compared to other missions with this level of ambition.

Alan Stern: Well, that's right. Typically, these missions to the outer solar system, take eight to 10 years to design, and build, and test, and have them ready for flight. We had some very tight timing. We were selected from that competition by NASA on the 29th of November 2001. And, there was only one Jupiter launch window that we could make, and we needed Jupiter to make this all come together the right way. That was in January of 2006, so we only had four years and two months to do, what I said earlier, typically took eight or 10 years for missions like Galileo and Cassini and Voyager. So, it was seven days a week, and 52 weeks a year that entire time. It was quite a sprint.

Mat Kaplan: And again, a lot of this is documented in that book Chasing New Horizons, which I do highly recommend. It's still in the library behind me. Let's start working our way out of the solar system. You mentioned that 2007 Jupiter flyby, and you picked up science there too, of course, but if you don't mind, let's head straight out for Pluto, because the science keeps rolling in. I mean, what's the latest news and science from that gorgeous world, and its nearby neighbors?

Alan Stern: Pluto is gorgeous, in so many ways, from being the little planet with a heart on it, just to the amazing variety of geology, and its beautiful blue atmosphere and hazy skies, and its satellite system as well. At the time of the flyby, I think I famously said, "I thought the solar system had saved the best for last." And, I haven't changed my mind. Pluto continues to astound us. It took me almost a year and a half just to get all the data back. I often felt like we were doctors in an emergency room, just triaging patients and stabilizing, except our patients where the data sets.

Alan Stern: We made hundreds of different kinds of observations of Pluto and its five moons. Color imagery, black and white maps, composition maps, atmospheric spectra, plasma data from two different plasma spectrometers, radio science, and as I said, there were hundreds of observations. At first, we were just skimming the cream off the top, what do we see? Let's report it. But, as time went on, and we got all the data on the ground, and we got through the first review of all the data. There was time for more considered thinking, for computer modeling of the geology, the geophysics, the geochemistry, the atmosphere. And then, there were new discoveries by looking harder at the data, or by integrating different data sets together to see how they told or supported a story.

Alan Stern: Pluto just continues to get more and more complicated. For a small world, it really is almost off the scale in terms of the geologic complexity and diversity that we see. But, there are a couple of themes to answer your question that have kept coming up over the last few years. One is, we see more and more lines of evidence that point to Pluto being an ocean world, having liquid water ocean in its interior. In fact, there's even evidence now by a NASA researcher and New Horizons co-investigator Dale Cruikshank up at NASA Ames Research Center. That this water from the interior has flooded out onto the surface in some places, and it carries with it organics. So, this is really interesting. The story is getting much more nuanced, and much more interesting from an astrobiological standpoint.

Alan Stern: The other thing that we see more and more lines of evidence for is cryovolcanism. A variety of different styles of features that look related to cryovolcanism across the flyby hemisphere. I think that's an interesting story too. And, all of those features turn out to be devoid of craters on their surfaces, meaning that they're young, that cryovolcanism may have been in Pluto's recent past.

Mat Kaplan: I read something else that indicates that this world is still pretty darn dynamic. There's something about a glacier.

Alan Stern: Well, the western side, the left side, if you will, of Pluto's heart is a vast nitrogen glacier. It's about the size of Texas and Oklahoma combined. I believe it's the largest glacier in the solar system, a million plus square kilometers. And, very early after the flyby, the detailed images showed these complex cellular patterns, geological cells, not biological cells, that Bill MacKinnon on our science team at the Washington University, and others in the planetary science community have interpreted as a sign of convection within the glacier, that it's overturning. And, one thing that supports that, besides the numerical models is the fact that that entire glacier is devoid of any craters at even the highest resolution imagery that we obtained. It's been age dated to be basically born yesterday, geologically. Possibly only millions or a couple of tens of millions of years old.

Mat Kaplan: Wow. Back to that water, that possible liquid water ocean that might be under the surface. Is this like Enceladus, where we are now almost certain that there is a water ocean, but for years, people thought, how could a body this small be hiding, or keeping water warm enough to keep it liquid? I mean, what's doing that at Pluto, which of course is ridiculously cold?

Alan Stern: Well, it is like Enceladus in some ways, and Europa, and other water ocean worlds in the outer solar system. It turns out they're pretty common, that most of the oceans in the solar system are on these faraway outer planet worlds. I think is something no one expected at the beginning of the space age when we began exploring the planets. We looked up with telescopes, and we couldn't find any oceans, and we thought the Earth was unique in having oceans in our solar system. Turns out we were completely wrong. There are oceans almost everywhere we look, in the satellites of the giant planets, Pluto and other dwarf planets in the Kuiper Belt almost certainly have these oceans, but they're all on the inside. Beneath a roof of kilometers or tens of kilometers of ice, or ice and rock depending upon the world.

Alan Stern: And, down there in the interiors of these small planets, it's warmer because of the pressure of the overburden of all those kilometers of ice. And, there are other energy sources also, in the case of the worlds like Enceladus and Europa, it's tidal energy from interaction between the orbit of the satellite and the giant planet host. In the case of Pluto, we're not sure really, it doesn't look like it's trapped heat leftover from formation, Pluto should have cooled off. But, it might be that that's what started the ocean. The rapid assembly of Pluto made it very hot in the interior. And, it may be that the oceans freezing which releases heat is acting like a battery to keep the ocean liquid even after all these billions of years.

Mat Kaplan: That's fascinating. My goodness. I wondered about what mechanism might be driving this. And if in fact, that liquid water ocean is there, and it as you've said, there's some evidence that that water may periodically make it out to the surface. Could it also have in common with Enceladus and possibly Europa, pushing some of that water out into space? I mean, you said evidence of cryovolcanism. What if we had a spacecraft like Europa Clipper that might be able to fly close to Pluto, and see if there's anything out there, maybe something organic to taste.

Alan Stern: Mat, you're thinking the way a lot of us are thinking, both about the science, and about the need for orbiter to go back and study Pluto in more detail, and with new kinds of instrumentation. I led the paper that looked for evidence of geysers in our imagery. We really looked very hard and didn't find anything. Now, it doesn't mean there aren't geysers on Pluto, because New Horizons was in that fast flyby, only able to map about 40% of the planet. The other 60% is terra incognita for the resolution that you need. We have low resolution maps of the far side. In any case, I think an orbiter going back would have an opportunity not only to search for those geysers like we've seen on Pluto's kin world, Triton. Voyager detected quite a number of geysers going off on that almost certain to be ocean world.

Alan Stern: But, in addition to searching with cameras, as you say, if there are geysers, or if the volcanoes are active, and in Pluto's low gravity, they're likely to cast material up to the high altitude, where like we did with Cassini, there would be an opportunity to fly through those plumes and sample that material. And, I think that would really be a blockbuster set of results if we could do that.

Mat Kaplan: Boy, wouldn't it. You've been making this argument for a Pluto orbiter for some time now. I read your December 2019 article in Astronomy magazine about this quest. Are you seeing any new interest in this from NASA, or possibly others?

Alan Stern: Well, there is interest. A lot of scientists in the planetary science community here in the United States signed on to the white paper calling for such a mission that's been written for the Decadal Survey. It's just now getting underway. But in addition, NASA last year selected 11 missions for study to support the Decadal. 11 possible future missions all across the solar system. Including an orbiter to Pluto, which is now in the final stages of that study to wrap up next month in August.

Alan Stern: I think there were something just north of 50 proposals out of which the 11 were selected. And, I think the fact that Pluto is in that mix is encouraging, but it also shows that NASA understands the priority of future Pluto exploration. So, we'll have to see what the Decadal Survey does with it, and with all the other great ideas for what we could be building in the 2020s, to fly in the 2030s. So, stay tuned, in a couple of years we'll know how that turns out.

Mat Kaplan: Yeah. And, our audience has heard us talk about the significance of the Decadal Survey, and how much it drives all of this. What may be happen in the following years. It's ironic, though, isn't it? If it had not been for New Horizons, that was such a struggle to get it into space, we probably wouldn't now be seeing this push for an orbiter of that world if New Horizons had not revealed it to us.

Alan Stern: Well, that's right. And, one of the great things about an orbiter mission to Pluto that we've discovered, both in internal studies that were funded at the Southwest Research Institute where I work, and now the NASA funded study, is that the curse of Pluto's low gravity that makes it hard to get into orbit, turns out to actually be a two sided coin. Although it makes it tough to get into orbit, it makes it easy to leave orbit, and go on exploring in the Kuiper Belt. So, a mission to orbit Pluto probably wouldn't end there. But, using flybys of the big satellite called Charon, the one that's the size of Texas. We can actually use those flybys to eject the spacecraft out of Pluto orbit, and back into the Kuiper Belt to go on to do more exploration in an extended mission.

Mat Kaplan: What are the biggest challenges of mounting a mission like this? I mean, I read that it could be a somewhat similar spacecraft to New Horizons, but you'd obviously have to do a few other things. I mean, for one thing, you'd have to be able to slow down to go into orbit. But, is that the biggest challenge?

Alan Stern: That is certainly one of the biggest challenges because Pluto is very far away, and moving farther out all the time, because its orbit is elliptical and it's on the side of the orbit that's moving away from the Sun now. To reach Pluto in a reasonable amount of time you have to go fast, but the faster you go the harder it is to stop. We have the capability to brake into Pluto orbit using the ion propulsion systems, the electric propulsion systems that missions like Dawn used. We don't have invent anything there. But, we have to carry the energy for that in RTG power supplies, nuclear power supplies. Because Pluto is so far from the Sun, you can't use solar arrays the way that missions like Dawn did.

Alan Stern: But, there are other challenges as well. One is that, I was saying a little while ago, our single fast flyby generated so much data that it took almost 18 months to get it back. You won't have an effective orbiter if just a few days of operations takes years to get all the data back. So, you have to much higher data rates to the Earth, so that you can take data all the time and keep up with it by sending it rapidly to the Earth. So, communications are a second challenge. But, I think the biggest challenge is just getting the funding. There's only a certain amount of money within NASA to do planetary exploration. The solar system is a big place there are demands, scientific demands to do more ocean world exploration which Pluto could count as.

Alan Stern: But, there are interests in many other kinds of missions. For example, going back to Uranus or Neptune. I would vote for Neptune myself, because Triton is there and that's another dwarf planet captured from the Kuiper Belt, in addition to all the wonderful things at Neptune. But, there are many, many good ideas that are going to compete in the Decadal. And, only a couple of missions of this scope, what are called flagships are likely to be affordable, coming out of the Decadal. And, we just have to see if a Pluto orbiter does well enough to surmount that challenge.

Mat Kaplan: So, many places to go and just not enough money to get to all of them. Wouldn't it be great if NASA's budget was maybe 1% of the United States federal budget instead of a half a percent roughly?

Alan Stern: We could all use that. If you think NASA is knocking our socks off with what it's doing with the current budget, that would be two and a half times its current budget, which would really be a bonanza for both human and robotic exploration, and of course, the study of the Earth.

Mat Kaplan: That's planetary scientists and New Horizons principal investigator, Alan stern. He'll tell us more after this break. Let's go another step out into the solar system. Three and a half years beyond your encounter with Pluto, to that New Year's celebration that I was able to join you for at APL, the Applied Physics Lab there in Maryland, and the flyby of Arrokoth. What we now know is Arrokoth anyway, the science is still coming from that as well. I mean, have you now, about a year and a half after the encounter, has all of that data been received?

Alan Stern: Well, actually, not quite. We've got all the pixels from all the instruments that were on Arrokoth, the Kuiper Belt object, but the surrounding pixels that we use for background subtraction, those on the black sky. And, for satellite searches as well, and ring searches are still coming to the ground. So, it's going to be a while before we get all of that, but you won't see new pictures of Arrokoth itself, or any new spectra because those are safely back on Earth.

Mat Kaplan: But, the science is still rolling out. I mean, you and your team had a big announcement in February of this year. Tell us about this work that may have helped solve, apparently one of the oldest mysteries about the formation of objects like Arrokoth.

Alan Stern: Yeah, absolutely. We had three papers published together in science in February, in a single issue that took a hard look at everything that we learned from that flyby, from composition, to geology, to origins. And, as you were saying, Arrokoth has been a tremendous gift to planetary science. We couldn't have asked for anything more in a small Kuiper Belt object, and none had ever previously been explored, of course. But, the geology and shape of Arrokoth, the contact binary nature of it, and the clear evidence of a gentle merger between the two lobes, points very strongly towards one of the competing theories of planetesimals formation, how the seeds of planets are formed, and pretty clearly rejects the main rival theory.

Alan Stern: The theory that seems to work is called streaming instabilities, or sometimes it's called pebble cloud collapse. It had been battling in the computers of planetary scientists making models with an older theory called hierarchical accretion. And, we couldn't really settle it with just theoretical modeling, it really took data in Arrokoth is a pretty clearly putting a nail in the coffin of hierarchical accretion, at least at this size scale in the Kuiper Belt, but possibly across the entirety of the solar system, we'll see with future missions.

Alan Stern: But, it's a very important result. I would put it akin to the discovery of the cosmic microwave background in 1965. That really settled the debate among which of three theories for the origin of the universe were correct, and made the Big Bang paradigm. Now we know that streaming instability, pebble cloud collapse, is the way that Kuiper Belt planetesimals, and very likely planetesimals across the solar system form.

Mat Kaplan: So, if we know how planetesimals get their start, we know how planets get their start?

Alan Stern: Well, that's exactly right, because the planets come from the planetesimals. They're built up from the nebula to small bodies like Arrokoth, to much larger scales like Pluto, and Earth, and the other planets.

Mat Kaplan: I had to dig out my old 3D glasses, the red and blue kind, so that I can enjoy some of the images, these 3D images of Arrokoth, which are pretty spectacular. Can you talk about this? And, was this also something that you did in collaboration with that astrophysicist who used to be in a rock band?

Alan Stern: You mean Brian May?

Mat Kaplan: Yeah.

Alan Stern: I think if Brian were on the show, he'd be telling me he's still in a rock band.

Mat Kaplan: Of course, Queen is still active, isn't it? And in fact, there was that great song about New Horizons that he premiered for us at your celebration.

Alan Stern: That's right. He actually wrote his first original piece of music since the late '90s, in honor of the flyby of Arrokoth by New Horizons, and it just blew us away. And, it's a fantastic song. It's an ode to exploration. And Brian, isn't just a hanger on, he's embedded in our science team and has been now ever since the Pluto flyby. He's on our geology and geophysics team, and he's one of our two experts for doing 3D topographic reconstruction, not just for Arrokoth, but Pluto, and Charon, and the other satellites. He's been on scientific papers, he's produced his own results from that. And, also work by Paul Schenk, another co-investigator on New Horizons down at the Lunar and Planetary Institute in Houston.

Alan Stern: We've learned that Arrokoth is quite exotically shaped as a what looked at first like a snowman. But, it's an unusual snowman and once we got the 3D, we could see that the belly and the head are both very flattened, which was a, "Who ordered that?" Moment, scientifically. But, which ultimately came back to supporting this theory of streaming instability, pebble cloud collapse. It may be very common among the planetesimals of the Kuiper Belt. When we just pulled one out of a bag, and this is what we got, what happens, you have to assume that you pulled the typical one out of the bag.

Alan Stern: And, I'm reminded when Galileo the spacecraft was on its way to Jupiter, it made the first flyby of an asteroid. The headline was, "The asteroid had a satellite." And, up till then no asteroids or satellites were known. It turns out it was completely typical. Now we know hundreds, if not thousands of asteroids that have satellites, and we know that they're common. And so, I think it's a pretty good bet that what we learned at Arrokoth, was typical of things in this region of the Kuiper Belt as a minimum, and maybe much more so across the solar system.

Mat Kaplan: I hope that our listeners will check out some of the links relevant to the New Horizons mission, and to you that we'll put on this week's episode page at We'll have to put a link to Brian May's song New Horizons there as well. I also have to say before we go further into the solar system. He was just delightful. He had a wonderful press conference while he was there, and he just seemed to be having so much fun. And, you're right when he premiered that song, played it for all of us in that big room at APL, it was the perfect ending for that evening.

Alan Stern: Well, I'll tell you he said something very funny to me the day after the song came out. I asked him, I said, "How's it doing?" He said, "In England it's number four on the charts." He said, "But, it's not going to go any higher because Bohemian Rhapsody is number three."

Mat Kaplan: He beat himself. Well, not bad. Not bad, though. Let's continue the mission. All those now AU beyond even Arrokoth. What's next for New Horizons? Do we have a shot at yet another flyby?

Alan Stern: Well, that's what everybody wants to know myself included, Mat. First I have to I have to say, and a lot of people aren't aware that we're doing Kuiper Belt science every day. We are sampling the plasma environment, the dust environment 24/7 essentially, as we transect the Kuiper Belt further and further out. And, we use our onboard telescopic camera called LORRI to look at Kuiper Belt objects in the distance, and study them in ways you can't because of our close range, and our unique observing geometries you just can't get from the Earth. So, we can learn about their shapes, their surface properties, and other attributes of these KBOs, Kuiper Belt objects, that you could never learn with any telescope that we have today on Earth or in Earth orbit.

Alan Stern: But of course, the big bonanzas come from flybys, and the spacecraft is healthy as we were talking about earlier, we'd like to find another flyby target. And, we have just since May begun searching for that. We are using some of the biggest telescopes in the world like the Keck. But, the most important one for us is the Japanese Subaru Observatory in Hawaii, because it has the best wide field camera for us to search with. We've had two runs now, one in May, and one in June on Subaru. And, we expect that we will discover, and I'm not exaggerating, hundreds of new Kuiper Belt objects along the direction that New Horizons is flying, of which about 10%, several dozen will come close enough to our spacecraft for us to study with that LORRI telescopic camera.

Alan Stern: And then, if we're very lucky, one of them will come close enough that with the remaining fuel we can actually get there in the next few years. The search is going to continue throughout 2020 and 2021. We don't have the data analysis even from the first ones done yet, but I hope that over the next two years, we do find another flyby target, because getting to a second Kuiper Belt object would be very cool.

Mat Kaplan: Happy hunting Alan. Look before we head out into interstellar space, which of course New Horizons is headed for as well. Are you adding to what the Voyager spacecraft have taught us about the edge of our own solar system?

Alan Stern: You mean about the heliosphere? Yes, absolutely. There's no question because we carry much more advanced instrumentation than they could build in the 1970s. We've been able to make the first detections of heliospheric particles called pickup ions, which are a very important component of the composition, if you will, or the census of the heliosphere, and also in the heliospheric pressure that sets the balance between the heliosphere and the interstellar medium further out. We're also carrying the first dust detector ever into this region of the solar system.

Alan Stern: And so, we're every month adding to the storehouse of knowledge about the distribution of dust which in turn tells us about the distribution of the larger bodies that collide out there to make this dust. We're studying the distribution of hydrogen in the heliosphere with our ultraviolet spectrometer tomoGraphing it, and making new discoveries with that as well. So, we really look forward to getting into what's called the termination shock in the 2030s, and possibly to the boundary with the interstellar medium towards the end of this mission.

Mat Kaplan: Do I remember correctly that that dust collector, was there student element? Was that a student built instrument?

Alan Stern: You're absolutely right, Mat. In fact, it's called SDC or the Student Dust Counter. It was built by students of the University of Colorado here in Boulder near where I live. And, it is in fact, the first student built instrument ever carried on a NASA planetary mission. Now they're very common. I think we broke the ice on that. Almost every planetary mission that flies has some component of a student built instrument or investigation aboard.

Mat Kaplan: What an amazing thing for those young people to look back at.

Alan Stern: Those students that built it in their late teens and early 20s, way back in 2003, four or five, are now well along in their careers. Some of them are now 40 years old. We have new students on the project all the time to analyze the data and operate this instrument. We've also had homecomings, and we brought back the original students who built all those years ago now, and brought them together. It's, like I said, a homecoming for the first ever student built instrument on a planetary mission.

Mat Kaplan: That's fantastic. Let's finish this consideration at least of New Horizons with, I don't know if it's your most recent major announcement, but it sure blew me away when I once again got out the 3D glasses, and took a look at what New Horizons is seeing from, not the Kuiper Belt, but from much farther out. Stars that are still amazingly far away, but among the closest to our own solar system. Tell us about this parallax imaging that New Horizons is enabled, as has never been enabled before.

Alan Stern: I'd be happy to. Thanks for asking. It's a really cool experiment. And, the credit for it goes to one of our team members, Todd Lauer, from Tucson, Arizona. He's actually a galactic astrophysicist, but he's one of the world's premier image processing experts. And, we put him on this mission to help us get the most out of the imagery of Pluto and its satellites, and Arrokoth, and so forth. Because he really is at the very state of the art. And, Todd had the realization that New Horizons could photograph the nearest stars and see them in different positions than we see from the Earth because of our great distance now out in the Kuiper Belt.

Alan Stern: It's the same idea, if you extend your arm in front of yourself and put a finger up, and then switch between your left and right eye, you'll see your finger jump back and forth. Well, because New Horizons is five billion plus miles away, the stars, the nearest stars, at least jump back and forth a little bit too. They're in different positions if you photograph them from New Horizons and from the Earth, and that's what we did in April. We had ground based observatories and amateurs who were photographing these nearest stars from the Earth, the same days that we did it from the Kuiper Belt. And, when you combine those images, then you can see those nearest stars. The two that we photographed are Proxima Centauri, the very nearest star, and Wolf 359, which is another of the closest stars, pop out of the image in 3D, because of our great distance allowing us to see them this way. In effect, New Horizons is seeing an alien sky, and allowing us to see it.

Alan Stern: We also use that data to perform in the world's first interstellar navigation experiment where without the need of the Deep Space Network, and all those tremendous tracking capabilities, we could from just those images, and the images made on the Earth, calculate the position of New Horizons pretty accurately, as if we were on a starship having to do it for ourselves enroute to one of those stars.

Alan Stern: It's been a very nice result, and I think it's going to be something that's in a lot of textbooks. There are very few things the Voyager team didn't do first, this is one. They probably could have, but once they turned their cameras off, they weren't able to do any more imaging. Because Todd Lauer thought of it, we were the first to carry it out, and we're very happy and proud to be able to do that.

Mat Kaplan: As you should be. It is absolutely striking to put on those 3D glasses and look at Proxima Centauri, and Wolf 359, which is what? About 7.9 light years away, and see how they jump out of the star field that surrounds them because they're so much closer. It is a true three dimensional view of our stellar neighborhood, at least this a limited portion of it. Absolutely fascinating, Alan.

Alan Stern: Yeah, absolutely. And, your listeners can Google that New Horizons parallax experiment, and find those images in the press release about them. Or just go to our website, which you said you would link on the page, and navigate to it that way. If they haven't seen it, I hope they'll take a look because it really is something unique and special.

Mat Kaplan: We definitely will include those links at I got just one more for you, Alan, and it brings it back home quite literally. You've been advising and working with Blue Origin, Virgin Galactic, other so called new space companies for quite a while. This fits in with, you've heard me call you the busiest man in the solar system. It looks like these companies, these Blue Origin and Virgin Galactic, if we're lucky, they may finally carry passengers on suborbital flights later this year. What's the potential for science up there? I know this is something you have some experience with looking back to some flights you took in an F/A-18.

Alan Stern: Yeah, I did a lot of airborne astronomy in my career aboard various high performance airplanes in NASA zero G aircraft. But, the F/A-18 Hornets were one of them. A U-2 derivative was another. It turns out that these suborbital tourist craft have the opportunity to do all kinds of research, and for that matter, education missions. Ranging from atmospheric studies to astronomical studies, to microgravity. And, because they're going to fly so often, it's quite possible we'll be in a new regime where we can do the experimentation you do in your lab using these spacecraft, where you can get data one week, and go back the next week and improve the experiment. Do it again, and again, and again, and again.

Alan Stern: And, the great thing about these suborbital spacecraft, from my perspective is that they're not only effective, but the cost of flying them, flying a researcher in an experiment is about 10 times less than a conventional NASA, or a military sounding rocket. So, we can afford to do much more science with these vehicles. My own team at Southwest Research, has built experiments and bought flights on these vehicles, and we're looking forward to flying as soon as they're ready, because the experiments are ready, and we're ready. We've done the centrifuge training, and the zero G training for it.

Alan Stern: Every two years, we host the meeting of the suborbital researcher community that attracts 300, or so researchers every time, to come and talk about what these vehicles can do in great specifics. And, I look forward to the next meeting. We just had one early this year. And, by the time we have the next one, probably in 2022, I expect that a number of people attending the meeting will have flown in space, and collected some juicy scientific observations as a result on these vehicles.

Mat Kaplan: Are you hoping to be one of those people who catches one of these rides, and gets up there above the von Kármán line?

Alan Stern: Well, absolutely. Yeah. Our team, as I was saying a little earlier at Southwest, has bought three flights, three seats on flights to fly our experiments, and I'm the PI of that program, so I'm expecting to fly with it. Absolutely.

Mat Kaplan: Alan, you've just given us another reason to stay in touch. I hope this works out. And obviously, all of us congratulate you on the great success you and the entire team of New Horizons, and its ongoing exploration out there. Getting close to the edge of our solar system, and looking far beyond it.

Alan Stern: Thanks, Matt, for having me, and for helping recognize, and celebrate the fifth anniversary of the first exploration of Pluto.

Mat Kaplan: That's Alan Stern, planetary scientist, space program executive consultant, and author. He's the associate vice president and special assistant to the president at SWRI, The Southwest Research Institute. Chasing New Horizons, that was his 2018 book written with David Grinspoon. The American Astronautical Society gave him its Carl Sagan Memorial Award, and he's been named to the Time Magazine's most influential 100 list, twice. We've got those links at, check them out. Back with Bruce and that comet in about a minute.

Bill Nye: Greetings. Bill Nye here, CEO of the Planetary Society. Even with everything going on in our world right now, I know that a positive future is ahead of us. Space exploration is an inherently optimistic enterprise. An active space program raises expectations and fosters collective hope. As part of the Planetary Society team, you can help kick start the most exciting time for US space exploration since the Moon landings. With the upcoming election only months away, our time to act is now. You can make a gift to support our work. Visit Your financial contribution will help us tell the next administration, and every member of congress how the US space program benefits their constituents and the world. Then you can sign the petitions to President Trump and presumptive nominee Biden, and let them know that you vote for space exploration. Go to today. Thank you. Let's change the world.

Mat Kaplan: Time for an abbreviated version of What's Up with the chief scientist of the Planetary Society that would be Bruce Betts abbreviated only because Bruce, as you know, we're not going to be answering the most recent question. Well, the second most recent question until next week, when we answer the most recent question. But, I'm so confused.

Bruce Betts: Yeah. Well, I didn't do it. And by the way, as longtime listeners know, I don't think we've ever abbreviated anything significantly in our history, but we'll see.

Mat Kaplan: I had coffee in my mouth, and it almost came out of my nose when you said that. But, it's true of course.

Bruce Betts: The caffeine is more effective that way.

Mat Kaplan: If you snort it? There's no abbreviating the universe. So, lay it on us.

Bruce Betts: No. Oh, what segue. Well played, sir. Well played. All right, we've got in the evening sky the Jupiter Saturn combination. Boy, it was just lovely looking at those the other night, being outside. They're coming up not too long after your sunset over in the east. Jupiter looking really, really bright as it does. Saturn looking yellowish to Jupiter's left, you'll find them over in the east, in the mid evening, I'd say. And then, coming up a couple hours later Mars also looking bright, getting brighter through October. It's all quite lovely forming a line. In the pre-dawn east, we've got Venus super bright getting higher, you can't miss it over in the east. And, Aldebaranon the brightest star in Taurus is snuggling up next to Venus particularly close on the 11th and 12th of July.

Bruce Betts: And then, the Moon joins in on the 16th and 17th. And then Mercury, not to be outdone, tries to struggle up as high as it can through the rest of the month over in the east, far to the lower left of Venus. But wait, don't order yet. This is why we can't do an abbreviated thing because comets happen. And, we've got comet NEOWISE, discovered by the NEOWISE spacecraft asteroid program, discovered a comet and it is visible in the pre-dawn east right now. It is theoretically visible as a naked eye object, but you're going to have real trouble, I would say, unless you're at a pretty dark site, but you might see it. My suggestion is always with comets is to try binoculars, get a finder chart online, go looking with binoculars, and then you can probably see it depending on how dark your site is with the eyes.

Bruce Betts: And, it's doing a tricky little thing. So, it's in the pre-dawn east for the next few days, but it's getting lower and lower. So, it will actually disappear from the pre-dawn. But wait, once again, don't order yet because it's coming back in the evening, just after sunset after its dance with the Sun. And, will be coming up, as few as five or six days later. So, say by the 20th, and then it'll be moving across the northern sky. We'll give you more updates. It's a comet. I've been burned by comets many a time, but sometimes they work out. So, go check it out it may be really bright. It may break up and disintegrate, it may hit Mat's house. We'll see. All right. Just kidding. Not going to hit Mat's house, we know that.

Mat Kaplan: But, it would be just because of my complaint to the solar system about how stingy the Kuiper Belt is with these objects, these dirty snowballs. I'm not going to get my hopes up. If you have binoculars, and if you are in a pretty dark place, under a pretty dark sky, you don't have to be in a really dark place, would you have a chance with binoculars of seeing the tail?

Bruce Betts: Yes, definitely. And, it's building, it's still short for a comet, but still pretty long. So yes, definitely. And again, from a dark site and looking at the right time, you'll see it all with just your eyes, but for many of us try binoculars. All right. Onto this weekend space history, two very significant flybys in space history. One, 55 years ago in 1965, Mariner 4 became the first spacecraft to successfully flyby and image Mars. And then, in 2015, you may remember, New Horizons did its flyby of the Pluto system, five years ago.

Mat Kaplan: They might remember that, since we just had been talking with Alan Stern about it. But, it-

Bruce Betts: Well, that's why I was wondering.

Mat Kaplan: Nice of you to remind them though. I'm reading a terrific book. And, we'll probably talk more about this on the show called The Sirens of Mars, and read this great chapter about Mariner 4. That's just a preview. I'll have more to say about that.

Bruce Betts: I look forward to it. We move on to random space fact. On average, Venus reflects about 77% of incoming electromagnetic radiation, in other words light at all wavelengths. 77% gets reflected. For comparison, for Earth this number, although it's varies is about 31%. So, not nearly as much reflected away. This fraction of incoming electromagnetic radiation at all wavelengths and angles is known in, at least planetary circles as the Bond albedo. There you go. There's your little education for the day.

Mat Kaplan: That's great. So, it's a mirror planet.

Bruce Betts: All right. Let's move on, shall we?

Mat Kaplan: We could move on. We have a new contest, but we don't have one for you to answer this week. But, I thought I would give people at least a little tease because of your question about... Remember you asked people to come up with a joke based on LightSail.

Bruce Betts: I did indeed, and I'm looking forward to them.

Mat Kaplan: So, here's just a sample, here is the aforementioned tease. And, this is from Stephen Trollinger. Where does the LightSail sleep when visiting, Bruce?

Bruce Betts: I don't know, where does it?

Mat Kaplan: On the photon.

Bruce Betts: Oh my God, that's actually funny. Well played.

Mat Kaplan: Stephen adds to that, "I'll see myself out." All right. Many more jokes next week. What have you got as a new competition?

Bruce Betts: Well, following along, here's your question, who is the Bond albedo named after? Go to

Mat Kaplan: Shaken not stirred.

Bruce Betts: Maybe. We'll see.

Mat Kaplan: I thought it was so ridiculous that I figured it was safe to say that, but I will say no more. You have until the 15th. You have until July 15th that to be Wednesday at 8:00 AM Pacific Time to get us the answer for this one, and win yourself A Planetary Radio T-shirt. How's that? From Chop Shop store. The, that's where the Planetary Society store is, you can check out all our merch.

Bruce Betts: All right. Everybody go out there, look up the night sky, and think about your favorite Bond planet. Thank you, and good night.

Mat Kaplan: No Mr. Betts, I want you to die.

Bruce Betts: No.

Mat Kaplan: Well, it's actually Dr. Betts, because he's the chief scientist of the Planetary Society, who joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. And, it's made possible by its ever questioning members, join us at And, will you leave us a review in Apple Podcasts or elsewhere? The solar system and I will thank you. Mark Hilverda is our associate producer, Josh Doyle composed our theme which is arranged, and performed by Peter Schlosser. Stay well, ad astra.