Planetary Radio • Dec 22, 2021

Discovering Mars with Jim Bell and William Sheehan

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Jim Bell

Past President (2008-2020), Board of Directors of The Planetary Society; Professor, School of Earth and Space Exploration, Arizona State University; Principal Investigator, NASA Perseverance rover Mastcam-Z instruments

William Sheehan

Astronomy historian and retired psychiatrist

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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

Space historian William Sheehan and planetary scientist Jim Bell have written a fascinating history of humankind’s at least 5,000-year relationship with the Red Planet. “Discovering Mars” is filled with anecdotes about the people who have revealed Mars. The chronicle includes Mars helicopter Ingenuity’s flights and then looks to the future of exploration. Someone will win the book in Bruce Betts’ latest What’s Up space trivia contest.

Discovering Mars book cover
Discovering Mars book cover Book cover for Discovering Mars: A History of Observation and Exploration of the Red Planet by William Sheehan and Jim Bell.
Mars: Valles Marineris Hemisphere
Mars: Valles Marineris Hemisphere A mosaic of 102 Viking orbiter images of Mars, showing a hemisphere of the planet centered on the immense Valles Marineris canyon system. Prepared by the U.S. Geological Survey.Image: NASA / JPL / USGS

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Trivia Contest

This Week’s Question:

Pluto was the first trans-Neptunian object discovered. Not counting Pluto’s moon Charon, when was the second trans-Neptunian object discovered? What is it now named?

This Week’s Prize:

A copy of William Sheehan and Jim Bell’s “Discovering Mars: A History of Observation and Exploration of the Red Planet.”

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, December 29 at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

Who do we have to thank for suggesting the planet name “Uranus?”


The winner will be revealed next week.

Question from the Dec. 8, 2021 space trivia contest:

Galileo discovered the four “Galilean” moons of Jupiter in 1610. When was the next one discovered, and which moon was it?


The fifth moon of Jupiter to be discovered, and the first since the four Galilean moons, was Amalthea, discovered by E.E. Barnard in 1892.


Mat Kaplan: Discovering Mars, 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. Humans have been discovering Mars for at least 5,000 years. The mission continues. And though the flow of data and facts has vastly accelerated in the last half century, the Red Planet's mysteries still haunt us just as they did the ancient Babylonians. William Sheehan, and Jim Bell have written a book that traces this entire history. It's terrific and so is my conversation with the authors that you'll hear in a couple of minutes. You'll also get your chance to win their book, when Bruce sends us out past Neptune for this week's What's Up space trivia contest. As I prepared this week's show, we learned that launch of the James Webb Space Telescope has been pushed back a few more hours.

Mat Kaplan: It's now set for the very early morning of December 25th, Christmas day. At least for those of us in the Americas and Europe. Planetary Society editorial director, Jason Davis has prepared a complete guide to the launch. You'll find it at Go JWST. Have you seen the mesmerizing, awe-inspiring video taken by the Parker Solar Probe, as it flew through the Sun's corona? It is one of the most spectacular space videos I've ever witnessed.

Mat Kaplan: Our CEO Bill Nye, worked with some of my colleagues to do a justice in the new video, it's on all our channels at Then there's our newsletter, the Downlink where you'll learn about an exciting find by the ExoMars Trace Gas Orbiter. The spacecraft has detected large amounts of hydrogen along the floor of the Valles Marineris Canyon. It probably means there's water down there in the soil, or at least water rich material. Might be a good place to homestead someday.

Mat Kaplan: There's much more at You know, Jim Bell, the Arizona State University professor has written bestsellers, including Postcards From Mars. Jim is principal investigator for Mastcam-Z. The sharp eyed 3D zoom camera that's atop the Perseverance rover's mast, and that barely scratches the surface of his past and present planetary science activity. Jim also served as president of The Planetary Society Board of Directors for many years.

Mat Kaplan: He is now teamed up with retired psychiatrists and longtime historian of astronomy and space William Sheehan. Sheehan has written many books, including one in 1996 that this new work updates extensively, the full title is Discovering Mars, a history of observation and exploration of the Red Planet. You'll hear me call it monumental. That's not just because it's big. The book is something of a monument to the thousands of scientists and proto scientists who have looked up in wonder at that flickering red wandering star.

Mat Kaplan: Here's what Bill Nye says about the book. "This is a detailed history of exploration to be sure, but it's really about the passionate characters, the humans with their telescopes and robots who have worked to know what goes on out there on this other world. As you read, remember, what we've discovered there over the last couple of centuries is amazing. What we'll soon learn about Mars will be astonishing."

Mat Kaplan: Bill is right. That's why I looked forward to joining Jim Bell in his ASU office, a few floors up from where his Mastcam-Z team was working with the latest images to arrive from the rover. Bill Sheehan couldn't join us in person so I put a microphone in front of Jim's computer speaker and dove in.

Mat Kaplan: Bill and Jim, thank you so much for joining us on Planetary Radio and for this outstanding book that every Mars lover or Areophile really ought to own. Thanks for coming on the show.

Jim Bell: Well, thanks for having us, Mat.

Bill Sheehan: It's great to be here.

Mat Kaplan: I already shared what Bill Nye said about the book. Here's a quote from our friend, Andy Chaikin, the author of the Man in the Moon. "Read and understand why we will never be done with Mars," which is a short and sweet, I would say. Bill, I think you and I got our first small telescopes in the same mid-'60s year and we both immediately turned them toward the Red Planet. Did that begin your passion for Mars?

Bill Sheehan: Certainly did. I mean, Mars was the main act really back then as in many ways it still lives. So as a kid getting everything I could out of the branch library and all of the books being several years out of date. So the idea that Mars might still be inhabited even by intelligent beings had not completely been exorcized from our imagination. So I was a believer at the time in the canals of Mars and had hoped against hope that that might all pan out. I certainly remember looking at Mars through a small telescope, one of those department store telescopes that everybody pretty much says they're worthless. But tell that to a kid of about 10 and seeing that little red disc up there, even though it was little bit bigger than a pin's head, it still was infinitely evocative to the imagination. So, yeah, that was 1965, March 1965. That was the opposition I got started.

Mat Kaplan: Just about the time I got my little department store refractor and that belief, that wanting to believe in the canals of Mars and that we might just find somebody up there to welcome us. That is a theme that runs through this book, how belief sometimes got in the way almost... Well, right from the start of the science, of the actual facts about the planet Mars. Jim, do you also see that thread?

Jim Bell: Yeah, absolutely. And it really starts with Bill taking the historical perspective and part of this book is an update to Bill's book from '96, I want to say. Yeah.

Mat Kaplan: '96. Right. The Planet Mars?

Jim Bell: The Planet Mars. Yeah. A lot has happened since then, of course, on the mission side, but a lot has happened on the historical side as well. Lots of research, lots of new photos and manuscripts uncovered, et cetera. And so yes, that thread of belief winds all the way through the historical side that Bill has researched so expertly and you know, it also runs through the spacecraft side. Right. We wanted to believe that the ALH84001 meteorite was loaded with Martian micro fossils. Some people want to believe there are human faces carved into the rocks of Mars. Right? Some people want to believe that we can do sample return in the next decade. Right? You know? And so yes, there's scientific facts. Yes, there's engineering reality, but yes, it's also a very human endeavor, this exploration of Mars.

Mat Kaplan: Bill, how did you get from that 1996 book, The Planet Mars to Discovering Mars and this partnership with Jim Bell?

Bill Sheehan: Well, I think one of the things that happened to me about 1965, because that was also the year of Mariner 4, which showed that there weren't canals on Mars. Instead, there was this stark, barren crater pock terrain that was revealed in those rather poor quality images. They were very gray, very bleak looking. So one of the things that happened to me at that point was that I wanted to understand how people, scientists could have gotten it so wrong. You know, how did they end up going down this primrose path into this very appealing, but ultimately elusory world that they'd conjured for themselves. So a large part of my subsequent interest in the history of Mars had to do with the way that the brain constructs a reality and then tests that constructed reality against objective facts that we can find out, whether it's with telescope, spectrographs, thermocouples on Earth or spacecraft.

Bill Sheehan: So I kind of took that story as of 1996, as far as I could, as someone who wasn't a trained planetary scientist. We'd only just gotten to the Pathfinder landing at that point and Vikings were already starting to become a bit hoary in history. Mariner 9 was almost an antique history. So when I was approached by the University of Arizona Press to do an update, 25 years had passed very quickly I might add, and I was totally unprepared to take the story forward. I knew Jim from many of his excellent books and in particular, the amazing photography that he has pretty much supervised and implemented on the surface of Mars. So I approached Jim and very generously, he agreed despite the fact that he's probably only sleeping four hours a night. Now, he might turn that back to three hours a night, and helped to bring this book up to date.

Bill Sheehan: Somehow we managed to do it, and it was a wonderful collaboration. I learned so much by doing this. As Jim said, a lot of the themes that started out really back in the time of the Babylonians, the Greeks, where Mars was already attracting human attention because of its intense red color and its sort of manic movements through the sky that continued right through the spacecraft era. And so I think even though there was some division of labor in terms of writing the chapters, I think that the book really is pretty seamless in the sense that these same human themes continue right to the very end.

Jim Bell: Yeah, it's true. And I'll just add, Mat. I'm a total fanboy of Bill Sheehan. Okay? When I was in grad school, it was Planets and Perception. And as a postdoc, The Planet Mars. These were some of my favorite books and they were impactful for me being a early career professional astronomer planetary scientist, learning how to observe places like Mars through modern instrumentation, to have that context of the history leading up to it and to have the context of the psychology leading up to it. You know, I experienced that first hand up on Mauna Kea for my thesis research, seeing Mars, the moon, other planets through lenses that were unprecedented. And so it became really easy to understand through great writing and perspective and psychological experience that Bill provides kind of what was going on historically.

Mat Kaplan: Bill, you probably don't know that for many, many years now, I have called Jim Bell, the Ansel Adams of Mars. But as you said, a fine writer as well. And however, the two of you worked out this tag team arrangement, it is a beautifully written and monumental book over 700 pages, including appendices. And I will note two of those appendices one by a current colleague, Casey Dreier, talking about what we've paid to get to Mars. And then of course our good friend who we admire so much, Emily Lakdawalla who provided another one of those.

Jim Bell: Yeah. Great getting those appendices in there. I don't think the whole calendar system and Mars time keeping system and the chronology that is presented in the book. I don't think that's ever been published in one place like this. And certainly haven't seen the great work that Casey's worked to figure out the cost of all of this and greatly justified cost of all this with references and resources and all that. That's certainly never been published in a book. It's been online, but here it is preserved in paper. And of course, and Bill went out and got some great appendices from some of his colleagues as well on Martian Nomenclature and other aspects of oppositions over history, et cetera. So it's partly, it's a resource for this kind of information that it's all in one place maybe for the first time.

Mat Kaplan: In the opening of the book, you both talk about how you got into this line of business. Well, particularly it's a business for you, Jim.

Jim Bell: Yeah.

Mat Kaplan: I think you came along a little bit after Bill and I got our telescopes, but you also talk about the one that you got. I don't think I've ever asked you how it all began for you. Your love of what's going on up there over our heads.

Jim Bell: Yeah, no, it was really two things. And you're right, I was not observing Mars in March of 1965. I was busy being born in July of that year. It's great to hear you guys talk about your histories. But in the '70s and '80s, I was fortunate to live in a relatively rural place with relatively clear skies on cold winter nights and have a family support to help me purchase a telescope, an eight-inch Meade Newtonian telescope, which I still have. Just wonderful to be out there and see while other kids are collecting baseball cards or whatnot, somebody always had a better Hank Aaron card. Nobody had a better Saturn, right? That's the real deal right there. And you could see the rings and I could see features on Mars and the moon, lunar craters.

Jim Bell: And so me and some friends I grew up with would be out there observing the night skies, getting to know that map of the skies. And then the other thing that happened in 1980 was Cosmos, the TV series, right? And so many people in my generation so profoundly influenced by one of the society's founders, Carl Sagan, who came along at a time when there was only three networks in PBS, on television, hardly any science on TV at all. Nova was around, still around, Amazing Show, but very rare to have real science on television and Sagan comes along and he's got this distinctive way of speaking and his turtleneck and his tweed jacket. You know, my mother loved him, right? Because he was speaking English, the technical language of planetary science and astronomy, but he was speaking it in a way that we could understand. And that was not a popular thing for scientists to be doing in 1980.

Jim Bell: But you know, it's on Johnny Carson. Right? It was just like having this direct conduit to a professional in the business that I was passionate, excited about as a kid was profoundly impactful.

Mat Kaplan: As it was for me. I want to get back to the book. It is monumental. In fact, I think there are about 230 pages of humanity's relationship with Mars until you get to the first time we successfully visit there with Mariner 4. Bill, there are countless anecdotes about the scientists, the engineers, the observers of Mars, how they did their work. There are also what may seem like detours from the main narrative that turn out to be at least in many cases, critical to understanding why some of the history happened the way it did. Now, one of those, and I think it goes back to what you were saying, Jim, about the psychology of all of this is color theory, which is also the first of the beautiful color plates in the book. How did color theory end up in a book about Mars?

Bill Sheehan: Well, one of the things that I'm fond of saying when I'm giving talks to people, I said, Mars is always been a master of illusion. First of all, it's one of the few very clearly red objects in the night sky. Bill Anders, when he was on Apollo 8 had said, "You know, the Earth was the only blue thing in the sky. Everything else was pretty muted." Well, Mars is one of the only red things. And red is one of those things that really rivets our attention and the reasons for that probably have to do with it being an ambiguous stimulus. It both signifies danger like the red eyes of the poisonous African tree frogs. But it also is associated with some of our appetites, which is why restaurants always use red as their theme color. So you have to pay special attention to red stimuli to determine whether to approach or to avoid it."

Bill Sheehan: So, anyway, right from the beginning, Mars's color really set it apart and stirred our interest. Well, once Mars was observed in telescopes, it appeared to have had some bluish greens spread on somewhat reddish background. Humans being as they are reasoning from analogy thought, well, bluish areas must be seas and the reddish areas must be lands. Eventually as people analyze these colors more closely, they realize that as anyone that has color blindness can testify, we don't see colors in the same way, any two of us. And in particular, we don't really see colors separate from the background against which they're projected. And so eventually some of these... Ray Bradbury has a nice phrase for this, "You know, we've we found that in the case of Mars, the blues were not really blues. They were actually rather neutral brownish areas on Mars, grayish areas. And it was just our way that we generate color information in our brains that made us see it in this way."

Bill Sheehan: So yeah, that all sort of took us down that what seemed to be somewhat of a detour, but it ended up being an important detour because so much of what we've made out about Mars's potential to be an inhabited planet had to do with our interpretation, either of Mars having seas or later vegetation tracks. I recently read an estimate that ranged the probability that Venus's clouds might have some sort of life. Depending on what an initial assumptions you make, it can go from virtually nil to 1.0, if you pick the parameters correctly. Well, up until the 1950s, I think most astronomers would've said that the chance of there being life on Mars was about 1.0. They were almost sure that that was what they were going to find there. And a lot of that had to do with these now clearly mystery colors that so long we were entranced with.

Mat Kaplan: We're not going to be able to touch 5% of what is in this book in this brief conversation. But there are, as I said, so many of these wonderful anecdotes. I had no idea the Giovanni Cassini and Christian Huygens were rivals in 18th century France. I mean, how fitting that eventually two spacecraft carrying their names would, centuries later, travel together to Saturn. I should say that this book has a lot of the history, not just of our exploration and observation of Mars, but of the whole solar system. Jim.

Jim Bell: Yeah, it's true. Bill has done a masterful job of bringing that history, which is of course, extensive throughout astronomy more broadly focusing it on planetary science and specifically Mars observations. You know, Bill, I went back and looked at the initial correspondence, spent eight and a half years, it took us eight and a half years to get this done.

Mat Kaplan: Wow.

Jim Bell: Just between our own research and time commitments or other projects et cetera. Part of it was, I think we both worked really hard to fill the back of the book with extensive notes and references and details. People who want to go dive into the Huygens-Cassini TIFF, they can do that following some of Bill's own work and many others that he cites in detail in the notes. So in that sense, it's an academic work. It's not just, of course, we're trying to write for a more popular audience, but we're also writing for academic colleagues, students, others, trying to learn and come up to speed on the history, students of history, students of science history, students of science communication, Martians, et cetera. So I think that was partly what you're seeing is a result of that extensive research.

Mat Kaplan: It's not a blurb in the book, but Bill Nye told me a few days ago that he thinks this is going to be the reference work for students of Mars for a long time to come, because it is so heavily researched, and all those pages of footnotes. I got to mention one of their anecdote, which I just love, Bill. And it has to do with Asaph Hall, the discoverer of Mars's moons, Phobos and Deimos, who was still not a very well paid astronomer apparently, when he was working at the Naval Observatory and one night he received a rather special visitor. Do you know the anecdote I'm talking about?

Bill Sheehan: I do indeed. Yes. It's not every night that you're at the telescope and a very tall thin man with a top hat happens to wander in the period when the civil war is raging. So if, or what's my line, you would probably pick him up pretty easily.

Mat Kaplan: And he just wanted to see the moon. Right?

Bill Sheehan: Yeah. Yeah. And it just shows, you know? A friend of mine that worked at the US Naval Observatory said that during the... And of course, the vice president's residents is now on the grounds of the US Naval Observatory, and none of the vice presidents were interested except for Al Gore, who used to come over regularly. So it just shows that if somebody like Abraham Lincoln, despite all of the tensions that he faced, the difficult decisions, the fact that he was presiding over, what so far anyway is probably the most decisive period of American history still found solace in going up to the dome and spending a quiet evening, looking at the moon.

Mat Kaplan: Wish we had a few more presidents who make a side trip up the mountain of Mauna Kea, too.

Jim Bell: Yeah. Members of Congress.

Mat Kaplan: Yes.

Jim Bell: Governors, mayors. Yes. More the merrier.

Mat Kaplan: All right. We'll move forward. November 28, 1964, I did not know it was 305 years to the day since Christian Huygens had sketched Syrtis Major from the observatory he had in his father's house. Pretty significant day. I almost, Jim, began to think of it as two eras before Mariner and after Mariner.

Jim Bell: Yeah. Those parts of the Mariner era chapters, I think Bill and I worked pretty closely on those. It was the beginning of the spacecraft era. Of course, it was the beginning of the end of our telescopic understanding and the beginning of something special. And that really getting to know the place. I think we were both pretty delighted that the book came out right on the eve of the 50th anniversary of Mariner 9 going into orbit, and so there's all kinds of celebration happening this year, 50 years in Mars orbit almost uninterrupt- Well, certainly uninterrupted in terms of the spacecraft, almost uninterrupted in terms of the data. You know, we've discovered with NASA and other space agencies, this is how you get to know a place. You spend time there. Spend time in that environment.

Jim Bell: You know, telescopic observers didn't have that luxury. Every couple of years you get an opposition, some of them are good, some of them are great, but those are only every 15 to 17 years. And you get a couple of months where you get this big 20, 25 arc-second disc in your telescope, and then it's gone. Right? And then you're trying to follow it through the fuzzy murk of the atmosphere. And so being there, those great oppositions that are written about and cataloged in the book are the closest that we could come to being there at the time. And so they were very lots of high stress, just like a rocket launch or a spacecraft landing. You know, we've got a couple of months, we've got to have this telescope system ready. We've got to hope for clear weather and all that just as much stress as today's modern exploration milestones.

Mat Kaplan: I'll be back with Jim Bell and Bill Sheehan in barely a minute.

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Mat Kaplan: Mariner 4, which as you both mentioned in the book, revealed only a tiny portion of Mars and not very well. Images of 200 by 200 pixels. Jim, my God, you do a little bit better today. Don't you with Mastcam-Z?

Jim Bell: Little bit. A little bit, a little bit, but still, I mean, revealing. Right? It was sort of left up to the gods of celestial mechanics, Isaac Newton, and his buddies to figure out where that ground track would go for those flybys. There wasn't a lot of control over that. And of course, the imaging technology, the spacecraft technology by today's standards is relatively primitive, but by the standards of 1964, '65, super high tech, right?

Mat Kaplan: Yeah.

Jim Bell: Lots of excitement about the potential. Bill talked about this earlier. You know, what are we going to see? What are astronomers going to be vindicated? We're going to see these vegetation canal. You know, these river networks, whatever. It was bittersweet, right? Because yes, the spacecraft was successful. Yes, we got this technology out to the farthest reaches that we'd ever been able to take images. And, oh man, is it just the moon? Is it just the moon, with the thin atmosphere? So excitement, elation by maybe engineers and depression from scientists thinking that, "Oh my gosh, what have we done? Have we made a huge mistake in what this world is really like?"

Mat Kaplan: Yeah. Well, not just scientists, Ray Bradbury, me, Bill. I think you Bill, the New York Times, big headline declared Mars, the dead planet.

Bill Sheehan: Yeah. Even LBJ went up with that particular story, and made a comment about that and sort of said, having remembered the 1938 War of the Worlds broadcast with Orson Welles, maybe it's just as well, it isn't inhabited after all. But yeah, that was a devastating event in my life. It was like, there's no Santa Claus and being told that definitively, and it did affect morale at NASA. You know, there were plans to cancel the later spacecraft that we're going to build on Mariner 4's legacy, because the idea was, well, what's the point of going so far afield to just explore another moon? Now that's why I think a particular Mariner 9 whose 50th anniversary, we just celebrated, made such an impact because we discovered that Mars wasn't another Earth as perhaps had been thought of one time.

Bill Sheehan: It wasn't another moon either. It was itself its self alone. We realized it had its own particular geologic history that included the buildup of shield volcanoes, vast canyons that made the Grand Canyon of Arizona look like something that was in a child's sandbox. Also, we realized for the first time, because Mariner 9 arrived under these conditions, what earlier astronomers had largely missed. And that is that Mars is a planet of dust, that if you were to pick one theme about Mars, it said it's a very dusty planet. It has these gigantic dust storms that can cover the whole planet from pole to pole. Before that, people thought Mars had a relatively clear atmosphere.

Bill Sheehan: And so they tended to overestimate the thickness of the atmosphere and also failed to grasp what was shifting the features around that they observed in their telescope. It wasn't that vegetation was growing and changing and withering with the seasons. It was that dust was coming across the planet and covering swabs of it for periods of time and then being cleared away again. So Jim and his colleagues have written some significant papers on just how that process works. Yeah. That will be the biggest shock after the disappointment of Mariner 4, Mariner 9, that we really have an interesting world up there after all.

Jim Bell: Yeah. And look, I mean, we point this out in the book, dust is going to be a big thing from Mars into the future when people go, and I'm an optimist. I've dragged some optimism out a Bill as well in the book. People will go, and this dust, which they will have read lots about going back through the telescopic time and through the modern era, this dust is going to be a major, major nuisance. It's just going to be something that has to be dealt with every single day in air filtration systems and space suits and habitats and airlocks and wheels and other equipment on rovers and other vehicles there. That dust has been around on Mars for billions of years. It's accumulated and distributed globally because the planet dried out early in its history, because it went from a more Earth-like place to the Mars-like place it is today. And it's not going to go away anytime soon. So Mars dust is here to stay and it's going to be a major part of the future interactions with Mars.

Mat Kaplan: If it's not already obvious, we're concentrating mostly on the farther back in history missions of exploration to Mars, because we talk about the more recent ones. We certainly talk about Perseverance and Curiosity frequently on this show. I would love to talk about Viking. I was there at JPL, in von Karman Auditorium, standing with Ray Bradbury and other people when Viking 1 set down, but I'm going to skip over that way ahead of its time, those two spacecraft to the Mars global surveyor. And the beginning of some work on Mars that continues today by Mike Malin, Ken Edgett and Malin Space Science System, still a partner of yours, right Jim?

Jim Bell: Absolutely. Absolutely. The small company outside of San Diego led by a bunch of really, really smart engineers and scientists. They have now deployed, I think, more than 30 successful deep space cameras all over the solar system. You've seen these beautiful pictures of Jupiter from Juno. That's a Malin camera. The images coming back from Mars Reconnaissance Orbiter, the visible wavelength images from Mars Odyssey, the MGS cameras, the Curiosity Mastcam cameras, the Perseverance Mastcam-Z is just an amazing amount of incredible work. And Malin and Edgett themselves taking those measurements and from MGS the first super high resolution views of Mars, like flying in an airplane over the Earth and have really revolutionized our understanding of the planet. Again, like we did with Mariner 9. Every time we look with better eyes with sharper vision, we discover new things and learn more about this amazing planet.

Mat Kaplan: We've learned so much about Mars from other instruments that we've sent there. How about MOLA also on the Mars Global Surveyor, which revealed this amazing topography?

Jim Bell: Yeah. I mean, getting to know... For a time, I think it was the case that we knew the topography, the elevations, the highs and lows of Mars better than our own planet, because much of the sea floor hadn't been mapped at that resolution, or at least not publicly available at that resolution. So yeah. Getting to know the planet that way. And you know, MOLA is an example of what I call squiggly line instruments, right? Spectrometers, and Bill writes about the early history of spectroscopy of Mars in the 1920s and beyond, and measuring the thermal energy from the planet. Getting these just look like squiggly lines on graphs, that's where so much of the science happens. Yeah, the images are spectacular. I'm a huge fan of the images. Yes I am. But what we do with the images really buttresses and supports and contextualizes what we get from these super high tech spectroscopy and other LIDAR and other kinds of instruments.

Mat Kaplan: Gentlemen, it's going to kill me to skip over things like Pathfinder and Sojourner and how that, what was really, you say a technology demonstration mission, put us back on the road to Mars and generated so much public excitement. But I'm going to jump over the current era and go straight to the future, which is where you end the book. You end with an examination of this future of Mars exploration. You consider the huge challenge of getting humans there, and you described several of the proposed pathways and plans that have been laid out by this diverse collection of individuals like Robert Zubrin and companies like Lockheed Martin. I was proud, and maybe you were too, Jim, to see The Planetary Society's contribution mentioned, not the first time in the book that The Planetary Society's role in all of this came up.

Jim Bell: Yeah. Well, the Society is devoted to space exploration, space education, advocacy. You know, it's a group of like-minded people that think a lot about how do we explore our solar system? How do we get out into our solar system? I think maybe like me, they're optimists about this all happening. So this is why the Society tries to put forward principles for human exploration, tries to guide our favorite space agencies and Hey, keep this in mind that you've got a public out there that wants to support this, that does support this. So come up with some plans, come up with some timescales, come up with some reasonable milestones, reasonable budgets. Let's get some of our elected representatives super excited about this just like we are. That is a really important part of what the society does. It's not just enjoying pictures or enjoying telescopic images or learning how to tell time on Mars, whatever. You know, it's much more than that. I think both Bill and I thought it was important to acknowledge the role that the society and other organizations have played and will play in exploring Mars.

Bill Sheehan: Yeah. And I need to get more involved with Planetary Society. That's definitely something I'm very keen to do, because I think we talked about Carl Sagan earlier and how we need his voice today. He's one of the few people that had the stature and the eloquence to be able to cut through a lot of the superstition, nonsense, that floods the media airwaves these days. As both of you have eloquently said, I mean, in order to get the public involved with this, they need to be brought in at the level of understanding basic science, the scientific method.

Bill Sheehan: You know, I mean, we're talking about some stuff that's really exciting, but it's a little bit like trying to paint the third story windows when you're standing on a step ladder. I mean, you got to at least have a ladder that's able to reach to that level if you have any chance to doing the job. That's why The Planetary Society is so valuable. I think to a certain extent, even some of the billionaire short hop space missions are helpful because they do at least keep space in the public eye even though obviously they're recapitulating what was already done long ago.

Bill Sheehan: I think Mars really is at this point, our best destination for mobilizing that sort of enthusiasm on the part of society, but we've got to get people educated so they appreciate why it would matter to spend our tax dollars or private funds to do something like that.

Jim Bell: Yeah. That's a great point. And all of us involved with the Society from Bill Nye on down, all of us are constantly aware of the need. You know, why is this important? Share this, why is this important? What is this going to do for our planet? What is this exploration of the Solar System going to do for our species for each other? There's lots and lots of answers, and we try to get those answers out there.

Mat Kaplan: Bill, I'm going to go to you for what may be the last word. And it is very nearly the last word in this book, Discovering Mars, A History of Observation and Exploration of the Red Planet by you, William Sheehan and Jim Bell available from the University of Arizona Press. Here's the line right at the end, "The most important thing we have gained from the exploration of Mars is the view Mars has given us of Earth." Could you expand on that?

Bill Sheehan: Well, I think the whole thing started with Apollo 8 and Earthrise in 1968. For the first time, humans were able to contrast the beautiful oasis of the blue Earth rising over the stark gray barren surface of the moon. That view did mobilize people for a short period of time before they retreated back into the grandiosity of that that is so much a part of our species. But just the fact that we now have explored Mars to some extent and have been able to realize that even though it looks that way when you see pictures of it, it's not like the Arizona desert that you can just go out into with short sleeves and quaff your favorite drink on the patio. I mean, it's a very stark environment.

Bill Sheehan: Someone said actually, it was at a conference that Jim and his colleagues put on at Arizona State, but said that no matter how badly we screw up the Earth, it will still be infinitely more hospitable than Mars will ever be. So I think ultimately when you look back from the surface of Mars and you see that Earth, beautiful blue but not even the brightest planet in Mars' sky, actually Venus is brighter and you see the Martian moons frequently racing overhead and they're brighter. And then you realize, well, that little tiny bright object in the sky of Mars is all that we have, at least now.

Mat Kaplan: Some would say a pale blue dot.

Jim Bell: Some would say.

Bill Sheehan: Well, I was trying to avoid that.

Mat Kaplan: We never avoid that around here. Jim, do we go out there at least in part to find ourselves?

Jim Bell: Yeah, look Bill's right. You know, we explore out there to learn about ourselves here. Everything we do in space exploration, I'm convinced it's going to make life on Earth better. If we figure out how to sustain ourselves as a species in the harsh vacuum of space or low pressure environments like the surface of Mars or low gravity environments like the surfaces of asteroids, if we figure out how to actually build settlements and structures and extend our civilization, for real, beyond this planet, that implies a mastery of sustainable engineering that is far beyond what we have in our capacity today. And if that has happened, then we are using that engineering to make life better here on our own planet. I'm convinced of it.

Jim Bell: In some sense, the work that NASA and other space agencies do, I believe spurs that kind of innovation. It does it through technology and engineering, but it also does it just through the, frankly, spiritual side, inspiring kids and their teachers and motivating people to explore and to better themselves and to push ourselves individually or as a species farther than we've ever been pushed. This is what the space program does for us. Mars is the beneficiary of that and our species and our planet will ultimately be the ultimate beneficiaries of that.

Mat Kaplan: Gentlemen, thank you for this wonderful conversation. We are the beneficiaries of this great book, which was published just a few weeks ago, Discovering Mars. Stick around because you have a chance to win one on the new space trivia contest when Bruce Betts arrives for this week's edition of What's Up. Again, guys. Thank you very much.

Jim Bell: Thanks, Mat.

Bill Sheehan: Yeah. Thanks Mat. Great interviewer.

Mat Kaplan: Jim Bell and Bill Sheehan are the authors of Discovering Mars, A History of Observation and Exploration of the Red Planet, published by the University of Arizona Press.

Mat Kaplan: Hey, guess what? It's time for What's Up on Planetary Radio. Here's the chief scientist of The Planetary Society, Bruce Betts. Welcome back.

Bruce Betts: Thank you. We got a lot of good stuff in the night sky. Let me dive right into it, Mat.

Mat Kaplan: Oh, good. Lots of nice holiday gifts. Go ahead.

Bruce Betts: Yes, indeed. We'll start with the planet party still going on low in the west, getting lower. Don't miss the planet party with super bright Venus, lowest down, Saturn looking yellowish above it, and Jupiter looking really bright above that. And if that weren't enough, Mercury joining the party, although, again, everything's getting pretty low, but Mercury will actually be pretty darn close to Venus, but much dimmer on the 28th of December. We also still have comet Leonard, which is in the same part of the sky, but very much challenged by the glow of sunlight. So it's tough. It'll be easier for our Southern hemisphere listeners to see it, but it's still going to take binoculars. Coming up January 2nd and 3rd peaking are the Quadrantids, which I mispronounced every single year. Named after the constellation that doesn't exist anymore, the Quadrantids, whew, can be a really good shower, meteor shower, but they tend to have a very sharp peak. So check it out the night of January 2nd to 3rd. Great news on moon, new moon. So no moonlight to interfere. So check that out.

Mat Kaplan: One of my favorite holiday traditions getting to hear you try to say Quadrantids.

Bruce Betts: Yeah. I feel like I miss something here. I've gotten so... Oh, Mars. Mars is not that great, yet in the predawn east be joined by other planets in the next month or so that will be running away from the evening sky and joining the morning sky. Oh, if you have a telescope and you check out Venus right now, it's going through quite a phase like the moon does. It's going through a phase. It's very much easy to see. We're seeing part of the dark part, the night part and part of the day part. All right. That's enough of that. Onto this weekend space history, this I found interesting and coincidental, Mat. 42 years ago, December 24th, the same day that JWST, James Webb Space Telescope scheduled a launch 42 years ago to the day was the first launch of the Ariane rocket. Now that was of course the Ariane 1 and they're now on the Ariane 5, which will be launching JWST shortly after this comes out, hopefully. Also, 1968, Apollo 8 orbited the moon. First humans to orbit the moon.

Mat Kaplan: Let's light that thing and get that telescope up there. Of course, by the time some of you hear this, we'll know if the JWST has been launched on its way by that big Ariane 5 rocket. Pretty cool.

Bruce Betts: But we are ignorant and trapped in time. So we do not know. We will.

Mat Kaplan: Send us postcard.

Bruce Betts: Onto random space fact. As far as I can tell, I've only alluded to this before and never mentioned this just totally weird freaky, freaky fact. Neutrinos, lots of them put out by the sun also by stars flying everywhere about a hundred trillion, a hundred trillion, and maybe that's 10 trillion or one trillion, but a hundred trillion pass through you every second. There's so many of them and they're so weakly interacting. Trillions of them are passing through us every second. The amount of time I've babbled is just been incomprehensible one, and two, hard to imagine how many have done that.

Mat Kaplan: A hundred trillion here, a hundred trillion there. Pretty soon you got a lot of neutrinos on your hands or run going through your hands actually. I love that. Yeah. I've always loved that.

Bruce Betts: I had an astrophysics professor who said, "On average, a human will absorb one neutrino in their lifetime and you die once." And he said, "Is that a coincidence?" I think it is.

Mat Kaplan: Oh, come on. Correlation, not causality.

Bruce Betts: All right.

Mat Kaplan: I hope.

Bruce Betts: I'm not happy to do. No, I don't know it matters. I'll just try to stand. So you absorb fewer neutri- I don't know. Let's move on to the trivia contest.

Mat Kaplan: Are you saying there's a neutrino out there with my name on it?

Bruce Betts: Yes. We call it Mat. Mat neutrino.

Mat Kaplan: With one T.

Bruce Betts: Well, yeah, of course, because it's a strange neutrino.

Mat Kaplan: Yeah.

Bruce Betts: Okay. That didn't make sense. Let's move on to the trivia contest. And I pointed out that Galileo of course discovered the four Galilean moons, which he did not name after himself, but others did, of Jupiter in 1610. I asked you when was the next one discovered and what moon was it? How do we do, Mat?

Mat Kaplan: Here is the answer from our Poet Laureate Dave Fairchild. In Kansas, Amalthea is the moon that came in number five back in 1892, before Bruce was alive. The reddest object you will find in all our solar system, Galileo would have claimed, but sadly, he just missed them. It's cute.

Bruce Betts: I just thought that was amazing. It's right. Those four are so much larger. I just thought it was amazing that there are hundreds of years before the next one was discovered. And now there's known to be 80ish.

Mat Kaplan: Here's our winner, Jean-Marc Bonard in Switzerland. Man, we have listeners absolutely everywhere. Jean-Marc, I would love to deliver this on my own, your Planetary Society Kick Asteroid, rubber asteroid, but we'll just have to put it in the mail to you. Congratulations on your win there. And thanks for listening.

Bruce Betts: Most excellent. Congratulations.

Mat Kaplan: Tristan Zimmer, and a lot of other people talked about this discovery having been made at the 36-inch refractor at California's Lick Observatory, which is still in operation. I just am blown away by the idea of a 36-inch lens, not a mirror, but a lens that big, that just is amazing to me.

Bruce Betts: It's very close to the largest least functional refractor in the world at I believe 40-inches at Yerkes Observatory, little random telescope trivia for you.

Mat Kaplan: [Pavocamesia and Belarus 00:49:52] and others mentioned that it was Edward Emerson Barnard, E.E. Barnard, who discovered Amalthea. He was awarded, are you ready? The Bruce medal in 1917. Could it be that Dr. Betts is hiding the secret of his past from us? Well, yeah, among others.

Bruce Betts: They knew I was coming. They named a medal after me, early on.

Mat Kaplan: Someday, there will be an astronomer and chief scientist who... Okay. Norman [Kasoon 00:50:27] in the UK. Simon Marius had independently discovered the Galilean moons one day after Galileo, but he didn't publish his book on the subject until 1614, even so the names Marius assigned are the ones that we use today. Ganymede, Callisto, Io, and Europa, which yeah, probably disappointed Galileo.

Bruce Betts: Better than naming them after his benefactors, which Galileo wanted to do.

Mat Kaplan: Yeah. What did he call them? The Medician Stars? I think, after the Medicis?

Bruce Betts: Something like that.

Mat Kaplan: Joe [Putray 00:51:01] in New Jersey. Fascinating reading about the potential of hundreds of tiny moons. And he has a question for you, Bruce, when does a moon become a moonlet, and could a moon have its own tiny moon as some asteroids do?

Bruce Betts: Well, moon to moonlet is a... The IAU to my knowledge has taken no position on the term moonlet but I think it's cute for small moons, but I believe there's no definitive distinction. Someone can let me know if I'm wrong, but considering the confusion and naming going on, as we find small stuff, it wouldn't surprise me. I believe that theoretically, at least for a moon in a distant orbit, another moon is possible, but in a close orbit, it's not. But we haven't found any whether it's possible or not.

Mat Kaplan: Joe, I hope you found that as a nice an answer as I do. Just a couple more here. Bob Klein in Arizona. After missing a couple of weeks due to a family illness, I figured I owed you an answer to this one. Ganymede it up to you guys with truly puny answers. No need to Europa me into this. Thanks Bob. By the way, there's a message for you. Call is tomorrow, Callisto Morrow. That's a...

Bruce Betts: Nice.

Mat Kaplan: ... struggle. Finally, this very nice poem from Gene Lewin in Washington. "Oh tender Goddess, a gossamer ring radiates from where you lie, hidden from view to nurture Zeus away from Kronos' eye. Then in 1892 from Earth, your location was spied. Amalthea, a fitting epithet once just known as Jupiter 5.

Bruce Betts: Jupiter 5. Yeah, they all got numbers and were referred to with nice Roman numerals for quite a while.

Mat Kaplan: Not to be confused with Jupiter 2, which of course was the spaceship that the Robinson family traveled on with Dr. Smith.

Bruce Betts: I hate that guy.

Mat Kaplan: And the robot says, do you have another one?

Bruce Betts: Yes, I do. Something about totally different objects, but a similar format. It turns out I found this fascinating as well. That's why I'm sharing it as a trivia question. And I don't know why I am using this voice. The first trans-Neptunian object discovered was Pluto, of course, in 1930s. So trans-Neptunian spending most of their time out beyond the orbit of Neptune, not counting moons of Pluto. When was the next trans-Neptunian object discovered? And what is it now named? Trans-Neptunian objects first found in 1930? When was the next found? And what is it? That's not Sharon Moon of Pluto.

Mat Kaplan: You have until the 29th, that's December 29th, Wednesday 8:00 AM Pacific time on that day, the 29th of December. And as promised we have for the winner of this one, I'm holding it in my hand all 720 pages, Discovering Mars, A History of Observation and Exploration of the Red Planet, William Sheehan and Jim Bell. You heard how much I enjoyed the book and I bet you will, too. So good luck. And we're done.

Bruce Betts: Everybody go out there look in the night sky and think of your favorite planetary pun. Thank you. Cut it. I'm just so flustered. Thank you and goodnight. I'm all theocracy. No, nevermind.

Mat Kaplan: Callisto-morrow. No, you can listen today to What's Up. You can listen anytime to What's Up with the chief scientist of The Planetary Society who has been joining me for this segment on the show for well over 19 years now, that's Bruce Betts.

Bruce Betts: You know, in old time taverns, you could gain a mead if you ordered one.

Mat Kaplan: Where's the bouncer when we need him?

Mat Kaplan: Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by its members who love rolling across the sands of Mars. Come on or drive with us at

Mat Kaplan: Mark Hilverda and Jason Davis are our associate producers. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. Ad astra.