Planetary Radio • Jun 03, 2022

Space Policy Edition: Inside the Planetary Science Decadal Survey Process with Bethany Ehlmann

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Bethany Ehlmann

President, The Planetary Society; Professor of Planetary Science, California Institute of Technology; Director, Keck Institute for Space Studies at Caltech

Casey dreier tps mars

Casey Dreier

Chief of Space Policy for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

Caltech planetary scientist and Planetary Society president Bethany Ehlmann was a key player in the creation of the recently released recommendations that may guide solar system exploration for years to come. SPE host Casey Dreier talks with her about the process and approach that led to this influential document.

2022 Planetary Decadal Survey Cover
2022 Planetary Decadal Survey Cover Image: The National Academies


Mat Kaplan: Hello again, everyone. And welcome to this monthly Space Policy Edition of Planetary Radio. Here we are in June of 2022. I'm Mat Kaplan, the weekly host of Planetary Radio joined once again by our Chief Advocate, the Senior Space Policy Advisor for the Planetary Society, Casey Dreier, who I am sorry to say you're a little bit under the weather, huh?

Casey Dreier: Hey Mat. Yes, I'm sure you can hear it in my voice. My body is too busy making billions of copies of little virus particles. I'm sure you can all guess which one? So sorry in advance if I'm sounding a little horse today, it sounds worse than it is. I'm overall fine, but we'll get through this and I'll be back to my smooth velvety baritone next month.

Mat Kaplan: And I can say upfront that having just heard you conduct this great conversation with your guest this week, who happens to be Bethany Ehlmann of Caltech, the President of the Planetary Society. You definitely held your own. I don't think you need to worry about how well your mind was working, even if your voice is a little off.

Casey Dreier: It's always good to have a gut check on that. It's hard to objectively measure that internally.

Mat Kaplan: Well, it won't help Casey get over the virus, but it certainly will make us all feel better. If those of you listening to this who are not yet members of a planetary society, it's kind of like, you know, clapping your hands for Tinker Bell. This is our equivalent to that, go to, and Casey will, I'm sure just make a miraculous recovery in the time that we're talking here when you become a member of the Planetary Society and a part of everything that we do.

Casey Dreier: No pressure or anything.

Mat Kaplan: He's depending on you [inaudible 00:02:05]-

Casey Dreier: I'm depending on you guys.

Mat Kaplan: Well, I know that considering the state that you are in that you probably want to keep this quick. So where would you like to go from here? You just want to say something else about this conversation with Bethany?

Casey Dreier: Well, we'll be talking about the Planetary decadal survey, which we haven't yet talked about on the show. You can read my initial piece on it on We'll link to that. We'll link to some other reporting on it as well. Many of you know about the decadal survey, and we've talked about it even a little bit on regular planetary radio, but Bethany Ehlmann is not just a Professor of Planetary Science, and not just the President of the Planetary Society. She served on the steering committee, the top committee on this decadal survey, and she helped put it together, write it, consider it, argue it. So she was a great person to talk to about what's in there, how this comes together, which I think is a very fascinating and important piece of context to understand for how to interpret this. It's just a very useful summary of that in addition to the content that we have on So very nice conversation. She's very busy. It's great to have her here this month, talking about it.

Mat Kaplan: So busy that your time with her was limited. And I know there's at least one topic there, there has been at least a small development recently and that's planetary defense.

Casey Dreier: Absolutely. We just had a hearing in the US Congress, the Space Sub-Committee held a hearing on the new decadal survey, which is great for them to really focus on it. A lot of very positive pieces of feedback about it. Members of Congress, very excited about it. The decadal survey is sometimes referred to as the sword and shield of science, right? So it's the sword and that you can battle forward and say, these are our priorities, let's get them. And it's also very importantly, the shield you can defend the ones that we already have. And it was very much being used as a shield already when members of Congress were asking about NASA's proposal to cut over a hundred million dollars from the Near Earth Object Surveyor Mission, our space telescope that's in development now that'll hunt for potentially threatening asteroids. They're saying, look, the decadal survey, which for the first time considers planetary defense as a major area and an aspect of planetary science strongly recommended that NASA pursue neo surveyor as quickly as possible. And one of the top priorities of NASA for the next decade.

Casey Dreier: And so they were able to say, now that this report is out NASA, why aren't you following the recommendations of this decadal survey? So it's like doing exactly what it was designed to do. We use that too at the Planetary Society, we have our own set of advocacy priorities. One of them is very much generally aligned with following the decadal survey. And we have already released a statement saying that we intend to take up that sword and fight forward for all these priorities, and recommendations, and great missions included therein.

Casey Dreier: It's a very exciting potential next 10 years of planetary science. Again, as always, if we choose to pursue it. And that's one of the big keys for us in the next 10 years is getting you, your colleagues, your friends, and other space advocates around the world to work together, to support these recommendations, so we can discover the moons of Uranus, to land on and [inaudible 00:05:19], to go to Titan, to go to Mars, to go back to Mars. All of these exciting places, right there. As Carl Sagan always said in his opening essay, that he put in the planetary report number one in 1980, "These are worlds crying out for discovery, and it's time to heed their call."

Mat Kaplan: I love it. You don't sound sick at all in those thoughts, which were much appreciated. That is so much of our mission and our vision at the Planetary Society. All right, Casey, I'm going to let you get off the microphone here and we'll go to that conversation with Bethany and start reading between the lines of the decadal survey.

Casey Dreier: Bethany, welcome. We've talked a lot about the decadal survey in various episodes here in the Space Policy edition. Can you recap what this report is and what it's intended to do for the planetary science community?

Bethany Ehlmann: Hi Casey. Yeah, sure. Once every 10 years NASA and the National Science Foundation request that the National Academies, the National Academy of Science Engineering and Medicine conduct a survey of planetary science. It comes with some very specific guidance of areas to investigate and come with recommendations as to what the program should look like in the next decade. And then the National Academies convenes the broader scientific community to participate in this effort and to give NASA and NSF the advice that they have requested.

Casey Dreier: This happens for every NASA science division, astrophysics, earth science, microgravity, and others. So planetary science is the big one, and this is only the third planetary science decadal survey ever put together. Did you participate at all in the previous one that came out in 2011?

Bethany Ehlmann: I did not participate in the 2011 decadal survey. I was actually a graduate student during much of the time of its formulation. Although I actually did play a small role in the one prior to that, because I did an internship at the Space Studies Board of the National Academy of Sciences when I was an undergraduate. And that was the time the decadal survey, the first full planetary decadal survey was coming out. So I was part of putting together kind of shortened briefing packets for Congress and policy makers as to the content of that first decadal survey.

Casey Dreier: It's a report at the end of the day. It's a good report. Everyone needs to read it. We'll link to it in the show notes, but the process of coming together, this is the fascinating thing to me that I want to spend a little bit of time on before we start hitting the main points of what the report actually says. You served on the steering committee this time you helped also, I think, chair the subcommittee, or what would you call them on Mars? [inaudible 00:08:12]-

Bethany Ehlmann: Right. I served on the steering committee. I was vice chair of the panel about Mars. And then I also was a writing lead for one chapter and contributed significantly to others. So many hats.

Casey Dreier: Yeah. And so how much did they pay you for all of this work?

Bethany Ehlmann: Oh, this is a volunteer activity.

Casey Dreier: Dozens of volunteers. That's my point you have a scientist volunteering their time to put this together. And you kind of throw your hat into the ring or get nominated to participate for the National Academies. How do you approach that as a scientist, knowing that this report will help guide the future of planetary science, knowing that you're representing your field? Was that a heavy burden or a stressful experience on your shoulders? Or what was that like being on the inside this time?

Bethany Ehlmann: It was fascinating to play as many roles as I was able to serve in. And that really is a point I think listeners can appreciate that. We all have day jobs as scientists, either as teachers, researchers working missions, all of the above, and this is a volunteer activity, and a substantial one. And so it's a big thanks to all of the members of the community who participated in it. The National Academy's paid staff coordinates us, but all of the scientists involved are volunteers. I love this kind of thing actually, the process of stepping back for a moment of the day to day of the science, the day to day of the mission work and thinking about the big picture and envisioning the future, and then thinking about how to make that future possible. So there certainly is... On the steering committee, I was one of only a small number of folks who primarily studied Mars, and primarily studied water in the solar system, which are my own particular parochial interests in science.

Bethany Ehlmann: Of course I wanted to make sure that those topics were represented appropriately, but it was also a chance to really learn about the state of the field as a whole. I only check in once every 10 years or so on the state of knowledge of planetary formation or the geophysics of the interior of Uranus and Neptune, which are far from my specialty. So it was great to be able to hear about these different science topics from my colleagues who are experts in these areas. And it was also amazing to be able to think about how to invest, invest in infrastructure, invest in technology, invest in things like relationships between the human exploration program and the science program, how to invest in our workforce, all of these things that actually make planetary science happen.

Casey Dreier: I mean, walk us through very broad strokes before we dive into the outcomes here. The steering community starts, you get a statement of task from NASA saying, here's what we want you to study. And this is worth just mentioning a bit because it really sets the confines of what you, as the people writing the report and studying, get to even think about and talk about, right? Like what did NASA ask you to do specifically and how much leeway do you have as the committee to pursue your own areas of interest or additional commentary and recommendations?

Bethany Ehlmann: Sure. And I'll just say that any listener who wishes to can Google the statement of task for the planetary science decadal survey.

Casey Dreier: I think it's in the appendices of the report itself.

Bethany Ehlmann: It is in the appendix of the report itself. If you download all 700 plus pages of it, you said everyone should read it Casey, but I think everyone should read the highlights. And then it is therefore reference. Only the very dedicated should read it all. Although it is fascinating reading in that statement of task, NASA specifies first of all, the scope of the report. So something that was really important this year, there are a few things that were a bit different in a way that I think is important. NASA and NSF placed an emphasis on astrobiology that this was a report that was supposed to be about the state of planetary science and astrobiology, both. And that was explicit in terms of our scope.

Bethany Ehlmann: Something that was also explicit is that we were asked to consider how human exploration and science activities can and should interrelate with each other. And there's some very specific verbiage on how we were directed to consider that question. And we were also directed things not to consider. We were told, please provide us a list of your mission priorities, but hey, if the mission costs less than $500 million, don't do that. Just the ones that are really big. So, the statement of task is important in kind of prescribing what the activities of the survey are.

Casey Dreier: And again, you kind of are held to that standard by the National Academy Staff. And you have people who kind of make sure you address every point, right? These are very particular [inaudible 00:13:06]-

Bethany Ehlmann: Yeah, that's correct. It's actually a very formal process. The National Academies exists in order to sort of organize the nation's scientists to address questions as directed by the government. So NASA and NSF, and I should say, both were partners in this drafting of the statement of task. Although of course the advice is primarily NASA. There are of course, many important NSF programs in planetary science as well. They tell the National Academies what they want us to study, and then the National Academies convenes the nation's scientists and makes sure that the ultimate report is responsive to every aspect of what NASA addressed and does not cover things that were deemed outside of the scope.

Casey Dreier: To me, that's the key takeaway here. I mean, NASA's actually directed now by legislation to request decadal surveys every 10 years, but it's NASA making the request. So you are almost surveying NASA's kind of the customer here to the National Academies. So this is providing a service to NASA, and then also to the broader community. Let's start talking about this then. I want to start not with the missions, I think a lot of people have heard the top line with the missions, but I want to start with the questions and the ways in which this report differed from prior planetary decadal surveys in that it really structured around 12, or is it technically 13 major questions that fall into three areas? And I'll just list them real quick, origins, worlds and processes, and life inhabitability. And I always forget the exo-planetary stuff is that a bonus 13th question? Or is that...

Bethany Ehlmann: That's basically it. That's a bonus 12th question, yes.

Casey Dreier: 12th question, okay. My-

Bethany Ehlmann: Let me actually check that that's true Casey. Let me fact check myself here because everything kind of got, you know, how it went through different... Yeah. Okay, I was correct, yeah. It is a bonus 12th question. So the statement stands. Yes.

Casey Dreier: It's a 12th question, but it was a cross-cutting among all three of those. That's where I was getting my head mixing up. And this is what I found really interesting, and I think this is the way that I like to frame the decadal survey when talking about it, because I think it's so easy to focus on missions because they're tangible things, and they're exciting, and we all want them to happen. But at the end of the day, we're putting this report together because here are the things we want to know about. We want to understand what the questions are that we even are trying to have missions to solve, right? I want to hear you talk about the process of defining these questions. How do you even start with something as broad as planetary science or solar system exploration? Where do you even begin to understand what to ask?

Bethany Ehlmann: Yeah, well I think the title of the report, origins worlds and life, OWL, for short. So really encompasses what it is we want to know as planetary scientists and astrobiologists. We want to know how did the solar system and how did life come to be worlds and processes? How do these processes work on planets other than Earth? And of course, then the big question, is their life? Was their life? Were there habitats for life? So it really organizes into these fundamental questions actually quite nicely. And as you mentioned, it is actually unique. This was the first of the three planetary science surveys to be organized by question rather than by destination. I actually think that this is crucial and is one of the things that makes this report as strong as it was, because it allows people to resist the opportunity to parochially sort of fight for destinations and step back.

Bethany Ehlmann: First of all, to the bigger picture of why is it we're doing this? And what is it we want to know? And how do we figure out this thing, not just on one destination, but on many destinations. And so this was something that actually came as direction from NASA to the decadal survey to please organize the report around these questions. It was something that NASA had worked with the community in advance, so each of the destinations Mars, Venus, outer planets, small bodies, et cetera, has a, what's called an AG an analysis group. That is a group that regularly meets of scientists. So these analysis groups for each of the destinations had been asked, "Hey, talk among yourselves, suggest to us what the questions were." So there was this body of knowledge that fed into the decadal survey as to what the questions should be.

Bethany Ehlmann: Our first task actually as a set of members, and as a steering committee was to take all of those inputs and reconcile them to come up with the 12 questions that you see here. And then the remainder of the survey was kind of organized in this matrixed way where people were assigned to a particular destination panel, but then they were also assigned to particular questions, and also particular aspects related to technology, infrastructure, workforce, et cetera. So everyone was participating in different ways in ways that were nicely I think crosscutting in terms of getting us to talk to each other about how to make progress across different planetary bodies.

Casey Dreier: And for the listener it's chapter 22 on the third page has a good summary. This shows up throughout the report, but of the 12 big questions. I asked Robin Canup, who was the co-chair of the full report, because you look through these questions and these are really basic questions to some degree, right? Like evolution of the proto planetary disc or impacts and dynamics. The top line questions don't seem to be solvable. Like you're not going to say, "Okay, we've solved impacts and dynamics in the next 10 years." That's just a fundamental thing, that's like almost an endless amount of potential understanding.

Bethany Ehlmann: But then you drill down one level and then you get to the ones that are potentially solvable.

Casey Dreier: Right, and that's what she kind of brought up is that so the big picture questions, these are like motivating questions. And the way that I understood it coming out of that discussion was the pursuit of these questions, functionally defines what it means to be a planetary scientist. If you're trying to answer one of these big questions, is that something you'd agree with?

Bethany Ehlmann: I think that's right. You mentioned it impacts and dynamics. So let's just take that one and let's like drill down. So I mean, not the top level questions, basically how do impacts and dynamics work? But that's not useful. What's useful is the next level for how the report is organized. Because it then splits that into four questions. How have planetary bodies collisionally and dynamically evolved throughout solar system history? How did bombardment vary with time and location? How did collisions affect the geological, geophysical, and geochemical environments on planetary bodies? And how do the physics and mechanics produce disruption in cratering on bodies?

Bethany Ehlmann: So, these are actually things that you can go and measure, right? One can make measurements of the rock record. One can make observations from orbit of the cratering density on a body. One can conduct experiments, in the laboratory of high impact physics to understand what's going on in the mechanics of impact cratering. So it's that next level drill down that really gets to things that we can make progress toward the big picture. And that's kind of how science is. You have to go from these very narrow questions to the big picture and back and forth in order to really push the boundaries of knowledge.

Casey Dreier: Did you just do that off the top of your head? All the four sub questions?

Bethany Ehlmann: I did not. I picked it up when you said [inaudible 00:20:30]. I like it picked it up like, let me go and see and give an example here, because I could not do the impacts one off the top of my head.

Casey Dreier: I was just like, wow, you really?

Bethany Ehlmann: No, I'm not that good. [inaudible 00:20:42].

Casey Dreier: But I mean that's a great point. And to emphasize, yeah, so like you go to any one of these chapters, it breaks it down and it's these sub-questions really define maybe the immediate areas of interest within these broader topic questions.

Bethany Ehlmann: That's right. And I would say that if you're a graduate student who's really interested in impact craters, man, that is the chapter for you. Question number four in chapter seven is where to go because there's this nice summary of the state of knowledge. And then summary of the holes in the knowledge, and then each one of these question chapters has recommended activities at the end of the chapter that highlight across planetary bodies, what are the measurements that are recommended? What are the laboratory studies that are recommended? What are the telescope capabilities that are recommended? Like how do we make progress?

Casey Dreier: Is there anything that's surprised or excited you from the process of defining these questions? Again, you talked about briefly you're a professional planetary scientist, done this a long time, but as a working scientist, you rarely get to step back and look at everything, particularly from really defining these fundamental questions. Through that process, and debate, and engagement with your colleagues, did anything jump out to you that you just hadn't considered before, or surprised you?

Bethany Ehlmann: Oh, there are lots of fun moments and I'm not sure I can pull out any particular one. I would say that in some of the things that I worked on, I enjoyed taking a deeper dive into the state of knowledge on other planetary bodies where I had maybe considered the question for Mars, and maybe a little bit for Earth. But I didn't know the details of how it had been considered for the sub-surfaces of Enceladus.

Bethany Ehlmann: So questions about what controls the energy available for life. I think about that a lot for Mars in terms of thinking about, well, if the organism's not photosynthesizing at the surface, what kind of energy exists from chemical reactions in the subsurface? It's a very similar set of questions for Enceladus and Europa, but you have to make very different assumptions as to what controls the energy availability. So it was fun to kind of flip your brain back and forth and think about how would things apply in another planetary body. I also just have to say, I mean, I do not study gas giants or ice giant planets, but I did enjoy hearing from my colleagues, the state of knowledge of Uranus and Neptune and what was known about each and why they were different. I feel like I learned a lot.

Casey Dreier: Was that almost surprising by how much we didn't know? The report is recommending a new mission to Uranus and it was kind of co-equal with Neptune as a scientific importance with the argument being that these are understudied planets. Was that something that kind of popped out very early on when you're taking these questions to say, and then again, and I'd also emphasize that the state of knowledge is just really valuable to read through and say, here's what we know and what we've learned about all these places.

Casey Dreier: Is that a way that you use in a sense, like the comparative levels of knowledge, as a way to help prioritize your recommendations coming out for types of missions? Or how did that fall out? Because you have these 12 questions. How do you prioritize which answering ones over others? Because that's kind of what you have to do at the end of the day by recommending a set of missions one, two and whatever.

Bethany Ehlmann: Yeah. By recommending a set of missions to a set of destinations, this is where the dialogue comes in and the engagement of many other people in the survey. And I mean, it's over a hundred scientists, right, that participated in various aspects of just serving on this committee to say nothing of the many hundreds of white papers that were submitted by others in the community that were read by everyone who actually served on the panels and chapter writing groups. In some cases, a lack of knowledge meant, man, we have to go collect that data. In other cases, it was a circumstance where we knew something, but perhaps it was confusing, or it made much clearer what the next more sophisticated question was.

Bethany Ehlmann: I think one of the reasons that Uranus, and Neptune are such high priorities, is as you say, we understand so little about this type of planet. And yet, in exo-planet data we see many more Uranus and Neptune like planets out there. We have some ideas, but we also understand relatively little about why Uranus and Neptune are so different from each other in terms of heat flow, in terms of tilt on axis. There are some ideas but they need testing. That was one of the reasons for prioritizing Uranus after Mars sample return, as the next flagship start.

Mat Kaplan: Casey will be right back with Bethany Ehlmann, but let's first take a minute with Q otherwise known as actor, John de Lancie.

John de Lancie: Star Trek has always represented the hope for a better future. I don't think you can have that without pushing boundaries. And in the case of space, that is all that we're doing is pushing those boundaries and finding out more, always finding out more. And I think it's really important as a human being, as a society to be able to do something like that. And this is where we do it. 200, 300 years ago, we did it on sailing ships across the ocean. Space is important to me because it's kind of a metaphor for risk taking, tremendous rewards, possible rewards, being more expansive in one's thinking and opening oneself up to the infinite possibilities. Probably the biggest thing that differentiates Star Trek from almost everything else is the community in which you enter. Well, the Planetary Society is that type of a community. If you share like me the need to expand into infinite possibilities as my character does in Star Trek. And as I have said to Picard on more than one occasion, then certainly joining the Planetary Society is a good way to go. Join the Planetary Society.

Casey Dreier: I want to talk a little more about this prioritization aspect because I was again, thinking through this, how hard of a job this must have been, not just to form consensus, but even to evaluate. In a sense you are being asked, or tasked, or both to say, "What's the value of something unknown?" The scientific return from going to Uranus. How does that measure compared to the scientific return from landing on and Enceladus, which was the second ranked flagship mission choice. How do you evaluate something that's fundamentally... How do you say the value of the unknown return from Uranus is going to be greater than the value of the unknown return from Enceladus in this situation. Or is that too crass of a way to think of it?

Bethany Ehlmann: There's a few more aspects of nuance in there-

Casey Dreier: Please, yeah.

Bethany Ehlmann: Everything that ended up as a priority mission is of course something that the survey deemed valuable. Right? In a world of limited resource, if we had infinite amounts of money, or not even infinite, just double, we would do them both right? And so it's in a world of limited resources what is the best choice you can make for the near term? Now, a decade is a long time, but actually in the grand scope of hundreds of years of scientific history, it's actually pretty near term. One of the reasons, for example of prioritizing Uranus over Enceladus, Orbilander-

Casey Dreier: Orbilander, yeah.

Bethany Ehlmann: ... as a second choice, part of that had to do with the high importance of ice giants, both in our solar system and beyond, and our relatively high level of ignorance. Enceladus is of course incredibly interesting as an astrobiology target, as kind of a mystery of title forcing, in terms of why it's able to sustain an ocean, the physics of that are not fully solved. Prioritizing it second actually gives a bit more time to develop in situ instruments, and actually also has the benefit of the fact that for a launch much later in the decade, then the mission would be accessing Enceladus when the south pole, with those beautiful tiger stripes that are emitting plumes into space, of the ocean, that is actually in shadow now.

Bethany Ehlmann: And for the next more than 10 years, I forget exactly where we are in the solar cycle at Saturn, but that most interesting area is not actually illuminated for our space craft instruments to see for multiple years. You can fact check and insert something later, but maybe it's for 17 years I think is the cycle. There is a practical aspect to the prioritization as well. So that Enceladus Orbilander can go when that critical south polar region is illuminated.

Casey Dreier: And that's one of the reasons that Uranus came out of the top over a Neptune mission, right? Because the orbital efficiencies of getting to one over the other just kind of favored Uranus.

Bethany Ehlmann: Yeah. The orbital efficiencies of getting to Uranus are more straightforward than getting to Neptune over this decade.

Casey Dreier: We've hit on a few things, but let's just kind of tick through some of the major takeaways. We breezed by this, but let's not. Mars sample return. That was the clear very top. If I'm reading this that's the very top recommendation is to complete the Mars sample return campaign. It's a bit of an odd thing I would say, maybe correct me on this in that the decadal survey this time around inherited a project that had kind of begun under the last decadal survey.

Casey Dreier: And so it's not a new mission that you're recommending, but you're kind of endorsing the resources and commitment to complete this. And you put you the committee or the report put some constraints on it's like try to keep it within this budget range. If something starts to happen, don't cut out other missions just to overinvest in Mars sample return. You need to get more resources to do it. Was that something that was a [inaudible 00:30:49] or something that you really had the option to say... Or, is it just that the science case is just so strong for Mars sample return, that that was... It just seems like an odd situation to inherit, but at the same time, it kind of has the blessing, the endorsement of the decadal survey.

Bethany Ehlmann: So it was part of NASA's guidance to evaluate NASA's plans for Mars sample return, and whether they played an appropriate role in the research strategy for the decade. And so that allowed us the survey to make substantial recommendations regarding Mars sample return. Interestingly, the statement of task did not ask us to rank MSR. It just mentioned us to comment on whether it should be descoped or up scoped, and whether what NASA was doing was actually appropriate with regard to Mars sample return. This was something that was very much discussed as part of the deliberations in accordance with the statement of task. And so we had a number of invitations. NASA has a standing review board and multiple boards that have independently taken a look at Mars sample return. So we heard from them, we heard from implementers of Mar sample return.

Bethany Ehlmann: We heard from scientists, indeed, Mars sample return remained a priority of the planetary science community. It has been something that has been on the docket so to speak since before I was even born as an ambition of the Planetary Science Community. You can find reports on this from the late seventies, eighties about how to execute a Mars sample return.

Bethany Ehlmann: So the decadal survey did indeed prioritize completing it. Something that's unique about Mars sample return is it's of course a multi-mission endeavor split it up into sample collection, sample launch, retrieval, and launch off of Mars. And then the return to Earth aspects are all split. A key aspect of enabling that is really the international partnership with the European Space Agency. This is not something that NASA is doing alone ISSA, and our European friends are making substantial investments, particularly to the Earth return portion. And to that initial kind of recollection of samples on the surface. And so that's also one of the aspects that was considered by the decadal is that this is a multi-country endeavor, and is it the right thing to do scientifically yes. Was ultimately the verdict.

Casey Dreier: Yeah. I always like to say the earliest reference to Mars sample return that I found in NASA budget documentation is fiscal year 1978, following on after Viking to start a Mars sample return study. So this is a long time coming in. So, I mean, you would think just naturally that something has been a goal that long would have some intrinsic scientific merit. That's good to see it formally kind of endorsed.

Bethany Ehlmann: It does, and the reason it hasn't been done right is it's hard. We've finally gotten to a point where we have the technology such that we believe that it can be done within a reasonable cost and schedule. This was not the case a decade ago, but there's been maturation of technology efforts that we do believe that this is the case now. And so sample return is one of these things that it's not a once in a decade investment, it's like once in a half century type level of investment. Because if you think about, you know, by analogy to the Apollo samples, those came back long ago, but they're the gift that keeps on giving in terms of discoveries as we develop new techniques on Earth to analyze those samples. And the same will be true of the samples collected from Jezero crater, and it's surroundings on Mars.

Casey Dreier: So that's Mars sample return. I want to touch on a little bit more on Uranus probe and orbiter, which was the top new recommendation for new flagships. To you, what was some of the most compelling reasons to go to Uranus? What made it really rise to the top from your perspective?

Bethany Ehlmann: Sure. A key reason for prioritizing Uranus is that we know so little about ice giants. There are two of the planets in our solar system. We see them around other stars, but we don't really understand many aspects about them. Uranus has its extreme axial tilt. It has relatively low internal energy and heat flow though, relative to Neptune. It has a complex magnetic field and it has really interesting satellites, some of which have geological activity that maybe is recent. So a question is do some of its moons have interior oceans kind of like Europa or Enceladus? There are many things we don't know. And these are some of the questions about interiors and atmospheres. Like what are the compositions of these ice giants? How are their magnetic fields formed? And then how do their satellites come to be that are super important?

Casey Dreier: So we mentioned Uranus probe and orbiter, and a lot of good reasons to go there. What we've seen and written about already on And then we also just briefly mentioned the Enceladus Orbilander, which is kind of a cool concept I didn't even know about which was that an orbiter that would then land itself on Enceladus. But let's move on.

Casey Dreier: Everything really focuses on flagships because it's in the name, they're very exciting big missions. Talk a little bit about these mid-sized new frontiers class missions. So it's a bit of a different process for these, the decadal survey recommends, how would you characterize this? Not necessarily destinations, but mission types, right? Like a concept mission that then people can pitch, or try to achieve through their own detailed concepts. But how do you put together a list of types of missions, and how do you prioritize those? Was that a different process than thinking about flagships, or was that kind of again, looking at the science questions where do we need to go? What's possible?

Bethany Ehlmann: In the context of new frontiers missions, they are medium class missions in the parlance of the decadal survey, but they require substantial investment from each NASA center. And so actually the first question that the decadal survey dealt with was the question of should these medium class, let's talk in round numbers for a moment, billion, billion and a half dollar missions continue to be prioritized by the decadal survey as in the past? Or would it actually benefit the community more to do this in terms of just a strictly open competition as was done with the Discovery missions, which are about 500 million to a billion dollar missions. But small. Which are still not that small. We considered this question, there's benefits to competition because it allows perhaps more creativity from the community. Perhaps it allows a greater responsiveness to discoveries that might take place between the decadal survey being written, and NASA asking for concepts.

Bethany Ehlmann: But we ultimately decided that these are significant resource investments, and so having a broader body of scientists set what the objectives should be for the set of targets was actually appropriate. And we said that, hey, if NASA wanted to consider adding missions, that weren't part of the decadal survey, that NASA should convene an appropriate body, a larger body of scientists to consider whether to add something, rather than being it just strictly left to the whims of competition.

Bethany Ehlmann: Now, in that sense, though, still there were now approximately two dozen new frontiers candidates visiting bodies across the solar system, each with very different science from rovers on the moon to Landers on Venus, to landing on Centar asteroids, to missions out to the Neptunian system. There were all kinds of things on the docket. And this is where the decadal survey had a process of going through the body panels. So at Mars, at Venus, at the moon and Mercury, at giant planets, at ocean worlds, at small bodies, what were the priority missions? And so those panels internally came with some priorities, presented them to the steering committee. And then we actually also did an activity for costing and cost realism to figure out, does this mission actually fit in the medium box or is it really a flagship?

Casey Dreier: Yeah, there's a list of about, I think seven missions for the next new frontiers. What's it called six selection of the decadal survey that folks can look up in the report itself. All of them, again, really... Including Enceladus, multiple fly by mission, right? So that could even leapfrog a potential Orbilander. You already said Discovery is the smaller mission class that the report doesn't comment on. That's more to be missions of opportunity.

Bethany Ehlmann: Right. I'll just say the only way we comment on it is the suggestion of how NASA set the cost cap, but not on the specific missions themselves. That's [inaudible 00:39:48]-

Casey Dreier: Right. Though, I guess after increasing the cost cap, you could then talk about them, right? Because they were up to 800 million as opposed to 500. So then that's no longer a $500 million mission, but 800 million. So you could have listed them all. Maybe too clever, [inaudible 00:40:01]-

Bethany Ehlmann: Yeah. I think that would've been against the spirit of the rules because really the increase of the cost cap is actually, it's maybe worth talking about a little bit. Discovery missions for a long time, have been advertised as cost capped at 500 million. But there's some subtleties to that, that's cost capped phase A through D cost. That means from the moment you conceive of the mission until you have it integrated in 30 days after launch, of course, the reality is that mission costs continue long after 30 days post-launch. And so some of the discovery missions were really starting to push upward of 700 million even toward a billion dollars. So taking the cost cap and saying the cost cap applies to the entire mission end to end was really just a way of really kind of ensuring there's some transparency in there and that the accounting is clear to everyone really.

Casey Dreier: So include the whole operations, and then you've also recommended bumping up the cost cap for new frontiers, with some additional considerations on how to manage these types of long extended mission operations. I do want to touch on something that's an important new addition to the decadal survey this year, or this time around compared to last time, which is human space flight, which is compared to 10 years ago, actively attempting to land humans on a moon. Which is a source of interest for planetary scientists, notably. Compared to 10 years ago, which was just basically the space station, you didn't have a serious lunar program to consider. I was really surprised reading this chapter about how for all of the talk of NASA's planning the Artemis program, how little direct input the scientific community has into it.

Casey Dreier: So, this is something that you've really brought up as an important addition. What are some of the key takeaways from this recommendations for NASA to consider with Artemis, and how is that different than what's been happening so far in terms of how they're integrating science into human exploration at the moon?

Bethany Ehlmann: Probably the most important recommendation is the recommendation to make the effort, and do the planning now. So that science objectives are incorporated into human science objectives and that human exploration of the solar system can benefit, and address all of these outstanding science questions that we have. There are many reasons for doing human exploration and not all of them are scientific, and that's okay. But if we are going to be making a national investment in human exploration, it is an enormous opportunity to make progress on some of the most pressing questions in our knowledge of planetary science and astrobiology. Because you have to do things like build in mission requirements.

Bethany Ehlmann: If the astronauts landing on the moon are going to launch back off with 50 extra kilos of rock, that actually has to be built in early into the mission requirements so that the systems are designed to support that, that the volume, that the mass allocation exists, that the propulsion system is then appropriately sized, that the volume considerations are considered, it's considered how the astronauts collect the samples and whether they need any handheld instruments to triage and pick that rock, not that one.

Bethany Ehlmann: There's an element of just planning and cooperation that's needed for the human program to be able to accomplish high level science. Which I think is actually good for the human program too, because it helps sustain the reason it adds to the body of reasons for why we are going. We are going to make discoveries. We are going to advance knowledge of all humanity.

Casey Dreier: And a really exciting complimentary robotic mission recommended by the decadal survey, too, Endurance A with this wildly to me, wildly ambitious Rover that would rove around collecting lunar samples for hundreds of kilometers, thousands of kilometers, then returning it to human astronauts on the surface to then bring back with them. Really interesting ideas in terms of integrating these two programs in this kind of coordinated effort to explore on the surface.

Bethany Ehlmann: That's right. And if anyone listening wants to download the decadal survey, you can download it for free. You have to either cancel the email address thing or enter your email address and download it. I recommend actually starting with chapters 22 and 19, it's not often you read a book from the end to the beginning, but 22 covers kind of all of planetary science and 19 zeros in on these human exploration questions. And as human exploration at the moon, and then later at Mars really get serious there are these enormous opportunities to collaborate, to accomplish high priority planetary science that would otherwise be very hard to do. For a long time sample return from the South Pole–Aitken basin. The oldest impact basin on the moon has been a priority to understand its age, to understand its origins, to maybe pick up a piece of the moon's mantle that was excavated.

Bethany Ehlmann: All these things are priorities, but you know, it's actually very hard if you only get to land in one spot and return samples to make sure you're getting like all the right rocks. If you're able to rove, to pick up samples and then deliver those samples somewhere that an astronaut can take them back. It is actually a highly efficient way to utilize the best of robotic exploration, and the best of the heavy lift capability that a human mission brings.

Bethany Ehlmann: And similarly, for Mars, as a kind of look ahead, there are a number of measurements for example, of subsurface properties, where is there ice? Where might there be solid rock landing pads that work well to take back off of again? All of these things are important and key measurements to be made from Mars orbit as well. So there's also some recommendations in there about an orbiter mapping mission for ice and subsurface properties. Because there are these elements that allow really human exploration to just tremendously enhance what we do as planetary scientists.

Casey Dreier: Not to mention Mar's Life Explorer, which was the other medium class, roughly-ish kind of go for it look for life in the subsurface ice concept. Once Mars sample return is completed as well. So Mars gets this engagement on, let's continue to have some sort of orbital presence as you point out looking for these subsurface minerals, ices. And then also we know enough, I think is basically what the decadal survey says. We know enough to make a real stab at if life is going to be somewhere, here's a good chance of where we could look.

Bethany Ehlmann: Yeah. That there is a reasonable argument to be made right now that we should go and learn about habitability and search for martian life in some of the places that have been flagged as perhaps having recently held liquid water. Even if the answer is no, not there. We will find out something interesting about ice climate and recent habitats with water that is really illuminating for understanding Mars as a system. So having a Life Explorer focused on exploring these recent environments with water solid or liquid was prioritized as well among the kind of medium mission class.

Casey Dreier: So Bethany we're in the final minutes here. Looking forward, is this something you would want to participate in again in 10 years looking at the decadal survey? Or are you happy to sit on the outside and watch another group of scientists help craft the future of planetary science?

Bethany Ehlmann: It is something I would definitely not want to do annually as a very intense process. This was all conducted during a global pandemic as well, so keep in mind, all of this was done and coordinated remotely over Zoom. So a huge kudos to the National Academy staff and to the chairs of the survey, Phil Christensen at Arizona State, and Robin Canup at Southwest Research who just did an enormous job steering everyone in this difficult time and keeping everyone coordinated.

Bethany Ehlmann: But so many meetings. There were definitely weeks where it was 20 hours online for decadal survey business. Cannot do that every year. But I would be delighted to have the opportunity to participate in the process 10 years from now. I think it's really an extraordinary moment to sit back, survey the fields, survey the state of knowledge, and dream about what's next. Then figure out how to fit it into a practical vision. It's actually a lot of fun.

Casey Dreier: Well, Professor Bethany Ehlmann, Planetary Scientist at California Institute of Technology, President of The Planetary Society, and also served on the steering committee of the recent decadal survey. Thanks so much for giving us some time today and walking us through the work you and your colleagues did on this great report. We will recommend all of our members continue to reach out and read it, and we are happy to cover it. And again, we've [inaudible 00:49:12] a statement looking forward to supporting its recommendations in the next 10 years. So we got our work cut out for us.

Bethany Ehlmann: Great, thank you, Casey.

Mat Kaplan: Chief Advocate and Senior Space Policy Advisor for the Planetary Society, Casey Dreier talking to among other things, the President of the Planetary Society, Bethany Ehlmann, Professor of Planetary Science at Caltech. And as you made clear, Casey, somebody who was right at the center on the steering committee of developing this brand new planetary science and astrobiology decadal survey that you and she went into in great depth and just fascinating observations.

Casey Dreier: It's not an easy job. And there was so much I wished we could have talked about in particular, how do you get a hundred people to agree? You know, and that's at the end of the day, I always find that it's almost the miracle of... And this is, I think what ultimately always differentiates science from either commercial or particularly human space exploration, where you have a number of factors to consider in terms of prioritization, how you're doing stuff. But with science, you have some objective reality external to you, and your preferences that helps forge consensus over time.

Casey Dreier: Even though you have scientists who all have their preferred areas of study, their preferred areas of investment, what they find interesting and what they don't, if they can get together and they adhere to basic agreement to this is what the real world is out there, they can use that to forge and to drive themselves into common agreement right? This is why we have decadal surveys for science, but not for human space flight, not for other aspects of space exploration because science drives it at the end of the day. And that's why I was so interested to hit on the questions first, before the missions. Right? Because that's almost the hardest thing is understanding what your questions are, right? I mean, Douglas Adams wrote a whole book about this, basically, right? It's a harder question to answer what the question is.

Mat Kaplan: 42, by the way.

Casey Dreier: 42 is the answer, right? It's just an amazing process to go through, and on the Space Policy Edition, it's not so much the mission headlines though, that's important it's the process, right? That gets us to those. At the end of the day, the decadal survey is very well respected, very effective, and we are almost certain to see at some level a mission to Uranus now, because this recommendation came through.

Casey Dreier: That doesn't mean it will happen and that's what we need to be vigilant about. But it's the process is so respected, it's just broadly encouraged. So it's a very impressive process, it's again not easy. It takes a ton of time by volunteers who are doing that instead of doing their actual jobs, and it asks a lot of people so it's a great report. Again, I do recommend reading it, as Bethany says, chapters 22 and 19 are the good two meaty chapters, I think. And then the rest of it is if you want to really dive into the meat and potatoes of planetary science.

Mat Kaplan: So we have a path to follow laid out by the decadal survey. Rest assured as Casey says that the Planetary Society will be fighting for these priorities. And we would love to have you join that fight. You can do so at to become part of making sure that these recommendations by the decadal survey, the planetary science decadal survey actually become reality. Casey, if this is your brain on the virus, we should all be so lucky, not bad. You made it.

Casey Dreier: Happy to be on this side of things, Mat. We'll be back next month more clear headed.

Mat Kaplan: I've never been so happy to be conducting this virtually, but someday we have to do it in person again.

Casey Dreier: Yeah. I will stride like a Colossus among humans after this, with my boosters and the actual natural immunities. So I should be, at least for a few months we could do it in person.

Mat Kaplan: Hang in there. Get, well, Casey Dreier is we'll say it again Chief Advocate and Senior Space Policy Advisor for the Planetary Society. I'm Mat Kaplan of course we will be back with another episode of the weekly Planetary Radio next week. If all goes well, it will capture some of my experience at the recent Humans to Mars Summit from Explore Mars, took place just two or three weeks ago in Washington, DC.

Mat Kaplan: Hope you'll join us for that. And again, for the Space Policy edition in July with any luck on the first Friday in July. Thanks so much for joining us. We'll see you again soon. Ad astra.