Discovering life elsewhere: How can we be sure?

Mat Kaplan: Life or not life? That is the question or is it? 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. This may be the best conversation about astrobiology we've ever brought you. It stars no less than NASA's chief scientist, Jim Green, and the longtime leader of NASA's Astrobiology Program, Mary Voytek. They are two authors of a recent article in Nature that calls for a comprehensive way to evaluate claims about possible life, to coin a phrase, across our solar system and beyond.

Mat Kaplan: The holidays are upon us, can't decide what to give the lover of space in your life. My colleague, Kate Howells, will arrive in moments with some timely guidance. And waiting for us at the other end is Bruce Betts, who has news of a solar eclipse and a prominent meteor shower. Check out the image of our warm wet home world at the top of the November 26th down link. Does it look familiar? If you're above a certain age, you'll recognize it from the cover of the Whole Earth Catalog.

Mat Kaplan: It's the 1967 photo taken by a NASA weather and communication satellite that Ariel Ekblaw mentioned in last week's show. Below it are these headlines in our weekly newsletter. You've surely heard by now that Dart, the Double Asteroid Redirection Test got off to a great start on November 24th. We are now less than a year away from its deep impact on an asteroid called Dimorphos. There's an image of the night launch at planetary.org/downlink.

Mat Kaplan: The mishap with the JWST at its ISSA launch site in French Guiana did not cause any damage. NASA has pushed the earliest launch date back four days though to December 22nd. And tiny Ingenuity, that spunky little helicopter that has made Mars its home, flew 116 meters in its 16th flight. The whirlybird is returning to the Perseverance landing site to conduct more science.

Mat Kaplan: Kate Howells is the planetary society's communication strategy and Canadian Space Policy advisor. Her very full plate includes some of our biggest outreach effort along with some that may not make as deep of an impact, but could put a smile on the face of someone special.

Kate Howells: Yes. So every year around the holiday season, the gift giving and receiving season, we like to put out a space gift guide because space enthusiasts, I will maybe say space geeks like us, do tend to collect spacey things. And so, many of your listeners, many of our members are probably like-minded and are looking for things for their own holiday wish lists or things to buy for their loved ones to maybe inspire a love of space or foster a budding love of space.

Kate Howells: So we are here to support that. So we put together a gift guide every year. This year, we reached out to anybody who wanted to submit an idea and we got about a hundred suggestions that we whittled down to the best of the best. And now that list is available in our gift guide on our website.

Mat Kaplan: So we won't even get through all of the best of the best, but at least share some of your favorites. And then, I'll tell you mine.

Kate Howells: Yes. So my favorites, well, my favorites are all the ones on the list because I had the honor of curating the list. But my top picks are, there's two posters that I absolutely love. One of them says, "The sun is huge and has a representation of the relative sizes of the sun and the planets." Just to show you how huge it is and the companion poster is the moon is far away, which likewise shows the distance of the moon from the Earth with their relative sizes. And they're just so no nonsense, just the facts. And I find that very funny and pleasing.

Mat Kaplan: So that one is also on my list, the cosmic scale posters. They are terrific. You'll find links from all of these gifts so that you're able to get them. Some of them are even free. But do go on, what's your second one?

Kate Howells: Yes. My second one is earrings that show the solar panels on the Lucy spacecraft. And I'm biased. My mother's name is Lucy. And so, I already loved this mission for that reason, but it is also just an extremely cool mission. Listening to the planetary radio episode about the mission actually is what really got me to become a huge fan. I have already purchased these earrings for my mother, Lucy. So I've got that one ticked off my own personal list, but they're just really gorgeous and a great way to celebrate such a cool mission.

Mat Kaplan: I agree, even if they aren't adorned with diamonds. I mean after all Lucy in the sky is probably good enough. What's next?

Kate Howells: My final top up pick is the Dare Mighty Things Umbrella. So everyone who followed the Perseverance rovers landing on Mars saw that its parachute had a binary code message on it that space fans out there deciphered to mean, dare mighty things, among other things. I think it had the location of the jet propulsion laboratory as well, but the pattern has been replicated on an umbrella and it is just so cool looking. And it's such a great way to signal to the world that you are a space nerd. So some other person seeing you walking down the street on a rainy day might recognize the pattern and you have a new friend right there.

Mat Kaplan: What a great way to share your love of space and start a conversation. It's almost like a space war shark pattern or a war shark test. Great fun. That was also on my list. I will quickly mention some of my others. The JPL Visions of the Future poster series, which is one of those that you can get for free by downloading. I love all these things that project our wonderful future as an interplanetary species. Anything with the JWST mirror pattern, that iconic pattern of mirrors that we hope will begin to unfold in space in just a few days now.

Mat Kaplan: The JWST cocktail glasses or what you chose for this list. I do have a partiality for the Voyager golden record. You may be able to see it behind me in the video that you're able to see. So the miniature version of it on the key chain, which you included. And finally, the Voyager photographs from humanity's greatest journey for the same reason. I'm such a huge fan of Voyager, but then, aren't we all?

Kate Howells: Absolutely. It is the best.

Mat Kaplan: Can I add some of my others?

Kate Howells: Of course, please. You are an expert on all things space. So your recommendations are very valuable.

Mat Kaplan: Okay. Well, I won't make any telescope recommendations this year as I did last year, but how about three books? One of them is actually a two volume set. We talked about it with our friend, Andy Chaikin, a few months ago on the show. It's the special folio society edition of Andy's A Man on the Moon. It is absolutely gorgeous, not cheap, sadly, but if you want to have sort of the ultimate chronicle of the Apollo Program, especially through the eyes of the astronauts that made the journeys, this is it, man. It's just tremendous.

Mat Kaplan: I am still reading it, but Discovering Mars by William Sheehan and our board member, former president of The Planetary Society, Jim Bell. The PI for Mastcam-Z. It is the definitive book about humanities relationship with Mars for only the last few eons. It's a tremendous book and a little program note. I'll be talking with Jim and Bill Sheehan about it later this month.

Mat Kaplan: Finally, for the science fiction people out there who have not gotten to it, Kate, have you read Andy Weir's Project Hail Mary?

Kate Howells: No. Not yet, but I'm keen to. Definitely. Put that on my wish list.

Mat Kaplan: Yeah. Good. Don't wait for the movie. It's coming apparently according to Andy. But it is the best science fiction, hard science fiction I've read in years. There's one more area that we should talk about. And that is The Planetary Society's own gift opportunities.

Kate Howells: Yes. So with the gift guide, we always try to highlight things from out there in the rest of the world, but of course The Planetary Society, we have our own store full of amazing space things that any space enthusiast will love. So you can find that at planetary.org/store. There are also a number of other ways that you can shop spacey and support The Planetary Society at the same time. Of course, we always love when people buy memberships for themselves or you can buy a gift membership for a loved one, especially if you're trying to spark a love of space. That's a great way to do it.

Kate Howells: And we have a partnership with Betchart Tours. So I mean if you're really looking to splurge this holiday season, you can buy yourself or a love one, a trip to see a solar eclipse or see the night sky from a tall ship with an astronomer on board, all kinds of amazing excursions like that. You can buy commemorative bricks to be put in the paving outside of our headquarters in Pasadena, where you can engrave message, a dedication.

Kate Howells: There are lots of ways that you can give a gift that also supports our work. So we definitely encourage all of those. And they're listed at the end of the gift guide for your convenience.

Mat Kaplan: And my family has one of those bricks and I can highly recommend the Betchart Tours since I went along as sort of a chaperone society companion on one of those trips. They do a tremendous job. And one more item that you'll find at chopshopstore.com or planetary.org/store, the Planetary Radio t-shirt. Don't miss it.

Kate Howells: Oh, of course.

Mat Kaplan: I should be wearing one right now. Kate, wonderful guide to the gifts. And I hope you get everything you're hoping for this holiday season and we'll talk again soon.

Kate Howells: Thanks so much, Mat.

Mat Kaplan: These are exciting times for space fans. For many of us at The Planetary Society, the most exciting prospect of all is the opportunity to discover that life is not limited to a single planet in the universe. That just seems so unlikely doesn't it? My guest this week have been at the forefront of a search for decades. Jim Green has joined us many times mostly during his previous job at NASA headquarters as director of the Planetary Sciences Division. After 12 years in that position, he was elevated to chief scientist in 2018. Jim is also deep into the fifth season of his great podcast, Gravity Assist.

Mat Kaplan: Mary Voytek has led NASA's Astrobiology Program since 2008 as the senior scientist for astrobiology in the science mission directorate. She came to NASA from the US Geological Survey where she headed its microbiology and molecular ecology lab and serves on the board of the American Geophysical Union. She has worked in some of Earth's most extreme environments ranging from deep sea hydrothermal vents to Antarctica. Jim, Mary, and four other distinguished authors published their paper in Nature back in October. It's a sign of how sophisticated and comprehensive our search for life has become.

Mat Kaplan: And it made me want to invite them to join the conversation you're about to hear. Jim Green, Mary Voytek, welcome to Planetary Radio. Congratulations on the publication of this paper, which a lot of us have been excited about at The Planetary Society and which I think our listeners are going to love to hear about. Welcome to the show.

Jim Green: Thanks so much, Mat.

Mary Voytek: Thank you.

Mat Kaplan: I'm going to start somewhat obliquely, Mary, by asking you, since I just talked about your visits, you've made many of them to some of our planets most extreme environments. Was there any place you didn't find life?

Mary Voytek: So far, no. Every place that I've gone and most places that people have gone, there's been life. It's amazing what life on Earth has evolved to take advantage of in terms of niches.

Mat Kaplan: So here's my best Jeff Goldblum impression. Life finds a way. Was it always clear that what you were looking at was alive or evidence of past life?

Mary Voytek: So I have not done work at looking at ancient life and that is really a challenge. So in my own experience, I've gone to extreme environments, but one of the reasons I went to a particular area is because I already knew that there was life there. There was an expression. There was colored snow. So pigments are a really good clue that there's, yes, pigments, not for my dog. But, yes, colored snow or ice.

Mary Voytek: And so, most of the places that I've gone including when I was on adjacent cruise and looked at a hydrothermal vent system. This was an oasis of life in an area that was barren. My interest was to find out what it is that unified life in these environment, as well as what allowed them to do things differently.

Mat Kaplan: There's some active life right behind you there.

Mary Voytek: Yes. I'm sorry. My dog wants to be interviewed as well.

Mat Kaplan: And don't worry about that. Happens all the time. You could probably tell where I'm going here. The paper that was published October 27th in Nature begins with these lines. Our generation could realistically be the one to discover evidence of life beyond Earth, with this privileged potential comes responsibility. Which pardon the additional pop culture reference. Sounds like something Spiderman's uncle would say.

Jim Green: Or Carl Sagan.

Mat Kaplan: Or Carl Sagan. Absolutely.

Jim Green: Right. Oh, absolutely.

Mat Kaplan: Extraordinary claims, right?

Jim Green: Yeah.

Mat Kaplan: Jim, was it this sense of responsibility that drove you and Mary and four other authors to the creation of what is suggested more or less as a prototype in this paper?

Jim Green: In a way I think that did contribute to my state of mind. I have been so enthralled with what we've been doing and finding out about life in many different ways. Like what Curiosity and Perseverance have been doing. And those things are really exciting and we just continually get great little tidbits of indications of potential biosignatures that could be related to life. Also, the exoplanets. But the concept of being able to use remote sensing has its inherent problems associated with it.

Jim Green: It's not like as Mary said, "Go out in the field and uncover the rock, see something, then recognize, 'Oh, this is what I need to do.'" When you're doing your remote sensing, you got what you got. If you're in space, you're going to be making a set of measurements. But there's so many other things around that you need to know.

Jim Green: For instance, in exoplanets, I can anticipate somebody looking at an atmosphere of an Earth sized planet sitting at the edge of a habitable zone, observing oxygen in the atmosphere, and then does the speculation lead to, "Well, that means there may be a plant life on the surface taking that CO2 in and generating the oxygen, right?" Well, in our own solar system I can tell you what that planet is and it's Venus. Okay?

Jim Green: And, so, there's so many other things that you need. And so, how can we help talk about to ourselves, and then also to the public such sophisticated set of measurements, and then develop the next steps, say what the next steps need to be and put them in the right context. That was always bothering me. And the scale does it. I was head of planetary for 12 years, we were constantly picking missions and really going over each and every instrument to make darn sure they were at the technology readiness level associated with their phase.

Jim Green: And no one is going to get through a mission proposal without what we call a TRL, technology readiness level of less than six, all right? You got to be six or forget at it. That was such an important scale for me, because I used it all the time throughout my planetary career. It just made sense of could we possibly do that in this framework? And indeed, it started with a conversation between Mary and I and Daniella. It just a exploded from there. We thought, "Hey, this is a good idea. Let's pursue it. Let's bring a couple key other people in and really, really take a look at it."

Mat Kaplan: Is that [Daniella Scalise 00:17:25], one of the co-authors?

Jim Green: Yes.

Mat Kaplan: We have come so far, even though we have not, certainly not conclusively found evidence of life elsewhere, not yet, but could what you have proposed in this paper, this scale confidence of life detection or COLD scale, would we have been prepared to create it let's say 20 or 25 years ago or is a lot of this dependent on what has happened since then?

Mary Voytek: Oh, absolutely. I don't think we could have done it back then. We could talk very… The SETI people, for example, have the Rio scale. And if you look at their scale it acknowledges that you need to verify and assess what you hear and what you observed and stuff, but for us to apply something like that we needed to learn a lot more about what life is, what kind of impression it leaves on an environment or on a planet when you're looking at an exoplanet. It has to be a planetary scale phenomenon for us to notice it, if we're going to detect it remotely.

Mary Voytek: And I would say over the years, we and astrobiology have really learned from all the new things that we understand about, 25 years ago, people were just starting to do molecular techniques and just sort of understanding the components of cells in a way that is meaningful and the relationship of organisms to each other, biogenetic information that talks about evolution and knowing what we might be able to expect and learning more about how to put things into context.

Mary Voytek: I like to think about, I once said in a slide that astrobiology was 50 years of getting it wrong. And what I meant by that was we need to have some kind of certainty before we develop missions. We need to have some kind of understanding, but our understanding has just been, we put something forward and we make a measurement and it turns out that we measured something, but we can't really explain it because we learned something in biking, for example, we learned about the environment of Mars and the regolith and the effect that environment can have on the preservation of a biosignature.

Mary Voytek: And that just exploded into an area of research and understanding with the Allen Hills meteorite. We suddenly understood that much like the adage about pornography in Congress will know it when we see it, we were so certain we'd know life when we saw it and it turned out, no. There's lots of things that look like life, that are produced abiotically. And honestly, the astrobiology program really blossomed or really exploded at that point with us realizing that studying non-life process were just as important as studying life processes, because it turns out that, for example, we talk about amino acids used to be the big thing to look for.

Mary Voytek: Well, we know you can make amino acids without life. The meteorites show that you can get amino acids in materials that come from asteroids. And we don't think that there's life that's producing it. And so, we needed very much to understand sort of the possibilities and the null hypothesis, which this is not life. And that has been what really what's been happening over the past 25 years. An increase in techniques and our understanding about life, in general, even more importantly, our understanding of non-life processes.

Mat Kaplan: We should talk about this scale, which I want to make sure everybody understands, because this is clear in the paper. This is just a proposal. It's a conversation starter, right? Because you're not saying this is being handed down from on high. I don't know how you want to approach this, maybe as a tag team. But, Jim, start to take us through how this seven step COLD scale works.

Jim Green: Well, it starts out, of course, with a basic observation, as Mary said, a biosignature. Something that we know that biology-

Mary Voytek: We like to call them bio hints.

Mat Kaplan: Okay.

Mary Voytek: Because we're not sure, right? Bio hint.

Jim Green: It would've been better if it started out that way. But the term today is biosignature. And indeed, that starts the conversation. That's a COLD level one. That's where you are, you now have made that observation. We're now seeing like methane. Methane from Mars is a perfect example. Here we are with [inaudible 00:21:58] team looking at Mars with telescopes and seeing methane.

Jim Green: Well, that's great. You can make that announcement. That's really wonderful and where it's coming from. But we also know that he's looking through methane in our own atmosphere to see methane on a planet half an astronomical unit away. And with a really small signal that brings up, then, the second level. Ensuring the contamination. How well have we made that measurement? What are those sources of contamination? And indeed, looking through methane to see methane can easily confuse the signal.

Jim Green: Now, in that case, they were really great about having the ability to look at Mars under certain circumstances, such that Mars is moving and you have a shift of your signal away from the main methane band, and therefore, you then can model that better et cetera.

Mat Kaplan: Because it was a localized source? That was the assumption, right?

Jim Green: Correct. Tagged to Mars, moving away, Doppler shift, gives you a chance, a ghost of a chance and making that measurement and they were able to pull it off. Well, the next big step is let's get down on the surface. Let's find out what's going on. And that's, of course, where Curiosity just come in. And that would bring it up to level three. Do we see it on the surface or not? And the answer is, yeah, we do.

Mary Voytek: This is when we start talking about two, whether it makes sense. This is where we now bring in the environment that we're measuring something in. Then, we start talking about in the next set of stages, of levels, we start talking about, is this something that can be preserved? Does it make sense with the other chemistry or the other observations in it? If you're looking at a bio fabric, like in the case of where you're looking for say a stromatolite, is it in the right kind of rock where that could form or is it in a rock that has defamation that ends up looking just like a stromatolite?

Mary Voytek: And so, all these other, I would say just simply, the first part of the scale is did you actually measure what you think you measured and you didn't make a mistake and measure something that you contaminated? And the next part is really common sense. Does it make sense? It isn't that the last explanation is necessarily life, because that has to be more of an active hypothesis as well. But you need to disprove that it's not beginning. And that it makes sense in the environment that you've actually measured it.

Mary Voytek: And so, that's when, oh, I use the example of, if you think that you're observing oxygen production and you're attributing it to photosynthesis. Well, if the planet or body doesn't get enough light, it can't be photosynthesis. And I'm going to take this opportunity to talk a little bit more about one of the other goals. At least one of the goals personally, for me, of this exercise. One of my biggest job as the lead for astrobiology is managing expectations.

Mary Voytek: And so, I'm involved when a mission says they're going to look for life and like toning that down if they're not really going to, because I don't want to go out to anybody, other scientists, people in the public, the press, and say, "We're looking for life." And then, disappoint you because we're not going to find it because we didn't send the right instruments. It wasn't the right planetary protection level so that we can trust things. It's just, we really need to manage the expectations.

Mary Voytek: And part of it is telling the story of the search for life, which is captured in this scale. So the scale actually also sets out what you as an individual scientists or non-scientists should be paying attention as our researchers and our missions go about making measurements and interpretations and allows us to be excited by all steps. So that is no longer a, yes, we found life, or no, we found life, didn't find life.

Mary Voytek: It is, "Gee, we found oxygen in a place and we think it's life, but there's no light, so that's still really cool." That sets us off in trying to understand something else about how the planet functions through a biological process that would produce it. I think it's really important to emphasize that all of research is important. We should be excited about all of it for various reasons, even if it isn't a highly, even if it isn't an affirmation of life.

Mary Voytek: That isn't the question. The question that people should be asking is if you want to use the scale, where are we on the scale or how far are we on this journey towards finding life? What new did we learn about what it takes to search for it both good and bad? I mentioned about us getting wrong, but at 60 years of trying to accommodate lessons learned. Each time we make a measurement, we do that.

Mat Kaplan: That is such a great insight that there is a story inherent. It's embedded in the scale that you folks have proposed. There is a delightful cartoon that was released in the NASA press release that shows this long line of white coated scientist building a ramp, brick by brick, level by level. And I think we'll share it on this week's episode page at planetary.org/radio.

Jim Green: Good.

Mat Kaplan: I think that's part of what this is about as well, right? It's not a single discovery or a single researcher or institution, Jim?

Jim Green: Yeah. Going back to when I was head of planetary, had we got the scale and let's say, we're at a solid low level three for methane. Here's where we've gone with a Rover and the Rover has said, "Okay, the methane that we're observing from Mars is not coming from a volcano. It's leaking right through the surface. It could be coming from an underground aquifer."

Jim Green: It's the environment then where you now have that information. If somebody would propose clearly a level four for a mission and describe it in that manner, that this is the step we're going to take. I'd fund it in a minute. I mean as Mary stated quite, clearly, we should celebrate each and every one of those steps, because it's making major progress along the way. It then enables the community to be solidly behind the next set of discoveries, the next set of missions needed. And enables us to describe it accurately to the public of the accomplishments that we have made and our next steps after that.

Mat Kaplan: It will be a big help to people like me who have the job of then translating this and putting it out to the public, which I know the two of you are also heavily involved with. NASA's Jim Green and Mary Voytek will be back in a minute when Jim will share big personal news with us.

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Mat Kaplan: I think we got to level three. You explained that. What is level four? And then, take us on up to level seven.

Jim Green: Four is all about, yes. Now, Curiosity is on the surface. It's measuring the methane. I said, "Oh, it could be coming from an aquifer." But it still could be coming from non-biological sources with magma and water and the right minerals, that interaction produces methane and it could be leaking where Curiosity is sitting.

Jim Green: So we haven't eliminated all the biological sources. So even though we talk about methane a lot, we're really at a solid three with methane on Mars. We haven't even made it to four yet. We have a waste to go. Even though we all feel that we've made just enormous progress in making methane observations at Mars.

Mat Kaplan: And we have.

Jim Green: Yeah. We have.

Mat Kaplan: But what is level four? How is it stated in the paper and in the graphic that's in the paper?

Jim Green: It's stated all known non-biologic sources of the signal shown to be implausible in that environment.

Mat Kaplan: I like your emphasis on the word shown, show me the proof, show me the extraordinary evidence. Yeah. So what's the next step up? What's five?

Jim Green: Well, five, we bring in additional independent signals from the biology detected. Now, what could that be? Well, I love the idea of the helicopter. What could the helicopter do? Well, we've flown on Mars. Ingenuity has done a fabulous job telling us here's a new tool. We believe from the maps we see from Earth that methane is coming from a number of areas. We know from Curiosity that it's leaking through the surface, but we don't really have a local map of where it might be leaking. Whether we could put methane instruments on the helicopter and go back and forth and back and forth over a grid, and then determine there might be an area or a swash where there's more methane leaking through the surface in another location, which draws our attention then to that area, to drill down, to go to that next step, to then really focus on going after that signal and perhaps finding it, the biology in an aquifer.

Jim Green: If a map came back and there was a streak across it, spatially, where methane was leaking through. That would give me a pause. "Ooh, what is that? Is that some sort of crack or some aspects of the geology that's funneling this methane?" And the methane could have been generated in ancient times too, and is being released through the surface for a variety of reasons. So that additional information is really critical for us to be able to make that independent set of measurements that then put the methane observations in a context.

Mary Voytek: So I also think that that level refers to you're measuring an organic that can be produced by biology or consumed by biology. And when biology works on a molecule, you can see isotopic evidence that it has been part of biology. And so, an additional type of measurement might be to look at the isotopic signature of that methane. And depending on both the hydrogen and carbon stable isotope assessment, it could further suggest biology, because it bears the signature of methanogen, which is an organism that makes methane from the local CO2.

Mary Voytek: One thing I'll say is everybody loves the idea of isotopes, but you have to be really careful with isotopes, because isotopes really depend on the signature of the molecules that are involved in all parts of the reaction. So it's understanding the carbon signature for the source carbon, which in the case of methanogen would be carbon. And the water that's involved in that for the hydrogen.

Mary Voytek: And if you don't know that, just a measurement of the isotopic signature of the methane doesn't necessarily prove anything. If you can't show that there's been a change away from the source material by only looking at the product. So it's a bit tricky. You have to be able to measure the isotopes and all of those to be able to say it. But that would be an example of an independent measurement that could indicate biology.

Jim Green: How I think about it, carbon is carbon 12, 13, and 14. It's got six protons, six neutrons. That's a carbon 12 in its nucleus. 13 is add an extra neutron. 14 is add an extra neutron. All right? And 12, 13, 14 come in nature in some sort of ratio. All right? And what's great about life is life loves carbon 12.

Mary Voytek: Well, and I like to think about it about weightlifting. If you're going to use, if you need to use carbon, why not pick the lightest one? It's more work to pick up a 13 or a 14.

Jim Green: Right. So as ingenuity is running over this area, getting and accumulating, let's say the carbon or the methane measurements and looking at the isotopes, and they find it's a whole slug of 13 and 14, and that the ratio is much more of a natural one. That's a huge step. That's a huge step. That means we have more work to do to explain if there's light there or not.

Jim Green: On the flip side, if it was all 12 and you couldn't see any 13 or 14 in the methane, that's also puts it now more in the plus column. Still doesn't tell us it's life, but indeed those indications are important.

Mary Voytek: One of the things that people have also argued is if the signal that you see is seasonal. And I must take this opportunity to say most of what we're talking about is based on biology as we know it on Earth. And so, again, there's all sorts of other things that could be happening that would be good to talk about if we have time about life as we don't know it. But with life as we know it, a lot of the emissions of things like gases, like methane are seasonal. And they have to do with temperature, controlling the activity of organisms or the same thing is true with the emission of oxygen and light controlling it. And so, there's a seasonal component too.

Mary Voytek: So if you see changes in fluxes, if you're measuring a flux of a gas, and there's a seasonal change that's apparent. That's another, again, hint that it might be biological. And so, I'm really focused on sort of these other things that people could be paying attention to that would support the idea that your initial measurement was biological.

Mary Voytek: I think something else that's true as well is kind of a back calculation. You see a signal, if the amount of biomas, the amount of organisms you would need to create that signal is of a particular size. I mean this is one of the things we have to do with remote sensing of gases. At some point, the signals are quite high. And if they're that high, that would mean you should actually be able to see the organisms, either in the atmosphere on the surface, because otherwise, you couldn't create such a huge signal, because many of these gases that we're looking at are reactive.

Mary Voytek: Again, you look at the flux. I mean oxygen is-

Mat Kaplan: Like oxygen. Yeah. Right.

Mary Voytek: Yeah. And that's great, but oxygen is really reactive. And if there isn't a continuous flux, you're not going to have it appear as a stable component of, or not a stable, but as a measurable component of your atmosphere.

Mat Kaplan: I doubt that we're going to have time in this conversation to talk about that other kind of life. I mean much as I love-

Mary Voytek: Agnostic biosignatures-

Mat Kaplan: Well, I love to talk about critters living on the surface of Titan that wear t-shirts that say, "I'm life as you don't know it." But we'll stick to what we know now. Are we strain into what might be level five on your prototypical scale or what does that, what gets us up to that next level?

Jim Green: Well, it's got to be more observations. The key thing about the scale is an honest assessment of where we are, and then understanding how to make progress by making it to the next step and really thinking critically about those additional measurements, the environment, much more about how we can through instrumentation, whether it's observing in different wavelengths on exoplanets, looking for other aspects that provide the context of the measurement you're making, as Mary mentioned, or indeed bringing samples back, the right samples that tell us something important.

Jim Green: So, Mat, I feel like you're tying us to the scale in a way that we start to become uncomfortable.

Mat Kaplan: [crosstalk 00:39:40]

Mary Voytek: Because the intent of this paper was to stimulate discussion, and just to think about… And that's part of the reason that I said the lower part of the scale is making sure you measured what you think you measured. And the other is starting to think about, does it make sense? And then, further up is can you confirm it independently by some other measurement? Whether it's a seven point scale or six or five or four, it doesn't matter. But those are really the fundamental discussion points.

Mat Kaplan: That's a good point. I mean I'm a member of the media. I want you to make it concrete for me, and then I'll tell everybody of that.

Jim Green: [crosstalk 00:40:14]

Mary Voytek: Every time we talk about a number, I start like, "No. No. We didn't want to put a number on it. Is there some way we can make colors?" Because, again, being a scientist, it seems as if that becomes quantitative and people want to be, "Are we at 2.3 or 2.7?" And it's really about those fundamental, again, scales tell you that you're going somewhere. There's a progression.

Mary Voytek: And so, we thought that was important to convey progression. And to say that there are kind of levels, but not to get tied up with the number. So I'm sorry if we dance a bit more than you'd like.

Jim Green: Well, we actually give other examples in the paper too. I mean we talked about oxygen. That's not in the paper. We talked about methane. That's not in the paper.

Mat Kaplan: Let's go to one that is in the paper. I was so thrilled in 1996, when all over the media, it was announced that these tiny structures had been found inside a Martian meteorite, found in that article. And it looked like evidence of long gone bacteria. I had to stop my car, get out and do a little dance by the side of the road, because we were still thinking life, not life, right?

Mat Kaplan: It wasn't very long before others made the argument against this conclusion that these little squiggles inside Allen Hills 84001 were micro fossils. If we had had the kind of tool that you have proposed back then, that would've made a big difference, first of all, in how it was being covered. But what level do you think that announcement might have come in at on this scale that you don't want to pin down?

Jim Green: Well, it starts with one. And then, the science community has to look at, well, we see these fossils, but we know that meteorite was on the surface of the Earth, which is teaming with life, as Mary said, for thousands of years. So was there contamination? What do we know about the rock that we picked up in Antarctica and brought back?

Jim Green: In fact, out of the activity that we do when we go to the Antarctica and pick up the meteorites that are there, bring back, and then cull through them and pick out the Martian ones. This was like one of only 11 at the time that we knew of. I mean it was a very early stage of being able to identify these Martian meteorites and then interrogate them. Had this meteorite come back in a sample tube that is what Perseverance is doing right now, knowing the context of it, with maybe a wonderful set of stratigraphy that is displayed in the rock that we drilled, that would be a different story.

Mary Voytek: I'd also like to point out that back then we stored things a lot differently and we thought that it was okay to store things in your refrigerator, and I'm sure everybody who's listening knows that things grow just fine in your refrigerator.

Mat Kaplan: Yeah. Sadly.

Mary Voytek: Lots of unwanted things grow particularly the longer they sit. And so, again, as Jim mentioned, the contamination was really a significant thing to overcome. And I think the people who are currently looking at meteorites, actually, I know. The people who are currently looking at meteorites have figured very clever ways to try to exclude signals from Earth life.

Mary Voytek: But the other thing, I think that to me, that really was sparked by that was, I think it's level three where we start talking about all three and four about the non-biological possibilities that created those signatures. We also, it also stimulated the little beads of cells. We started talking about, what is the minimum size of the cell? Because they were quite small. Smaller than anything that we knew. So we sort of challenged, started challenging it, what would create it non-biologically? And is it possible biologically? Does it make sense that you could have everything you need in a cell to function in something that was that small?

Mary Voytek: And I will say, one of the things that we noticed when we were talking about some of these examples is you can sometimes move up the scale, and then do more assessment and move back down and lose ground. So it always isn't forward motion.

Mat Kaplan: Not a diode. It's not straight up to level seven or whatever level people eventually decide on. Jim, I'm going to go back to that example that you were talking about earlier, because it presents so many other challenges. The challenge of finding life on a planet that is light years away. Well, let's say it's JWST, long may it gather photons. Finds that evidence of oxygen in the atmosphere of a nice little Earth-sized world, maybe it's right in the middle of the Goldilock zone, not too hot, not too cold.

Mat Kaplan: And then, it gets backed up by a similar finding let's say by the giant Magellan telescope. Is this now something which is going to move it up, whatever form this scale eventually takes, because it has come from at least two different instruments, but I mean you can't, you're not going to be flying out there to sample that oxygen or anything else on that world.

Jim Green: Well, indeed, you may be able to move it from one to two because you've now got complimentary observations using two different systems. But it doesn't provide yet the context, unless you're looking at different aspects of the environment, different wavelengths. Putting it in the context of perhaps temperature, putting it in the context of, do we see any signatures of water or other liquids based on knowing that life needs to metabolize and therefore requires a liquid as a solvent to extract energy and then eliminate waste?

Jim Green: That hopefully will focus attention on other observations that will be very important, that will then be in that context revolutionary in moving it up to scale, or as Mary says, down the scale.

Mat Kaplan: How has all of this been received, Mary, so far? I mean I know there's been a workshop and there actually is maybe been a little bit of criticism, perhaps from some folks who didn't quite understand where the six of you, you, the authors were hoping to go with this.

Mary Voytek: This was a call-to-action to the community to basically help out NASA. And again, I do want to emphasize that this is not something we're prescribing. We're asking for help. And a group of researchers in the astrobiology community got together and held a workshop to talk about standards of evidence. And they came up with their own scale and there's a white paper that's out for people to look at and observe.

Mary Voytek: It had great participation. I think there were 350 people that applied to participate, because it was virtual and they had to manage things. It was by application. And so, they selected people that there was a lot of people that wanted to observe and they were permitted to observe. And then, about 135 that actually were active in presenting in discussions.

Mary Voytek: And then, there's been all these opportunities for people to comment on it. I think that even the people that participated needed to understand that this wasn't in any way meant to prescribe what you would do scientifically. This wasn't to shoot down hypotheses. This was simply to remind people that if you're going to do this, just because it's an exciting topic like life. And particularly because it's an exciting topic like life, and people are hoping that you have found something.

Mary Voytek: You need to very strictly apply the scientific method and you need to be very careful with your interpretation. And it's not that we don't, we're saying don't do that experiment or don't try to find, come up with a new biosignature. That kind of creativity is what makes NASA NASA. And in fact, I remember when I first started working for Jim, he made it very clear that he wanted to make sure that our selections from our solicitations included those high risk, high reward. There's some intellectual risk in what they were proposing.

Mary Voytek: And some people describe that as career breaking. We are going into the unknown so often and we need people thinking outside of the box. So that is something we would never support. And this is not intended at all to be that. This is really about how you communicate what you have done in a way that people understand, and so that they can understand how far you've gotten. They can understand what you've did, did in considering what you have measured and what you have not measured.

Mary Voytek: It's almost more important to be able to say what you haven't measured, right? And so, this was just guiding people really in how to communicate their science and how to, to assure them that if we do this right, the public is going to be interested in our journey.

Mat Kaplan: Absolutely. Jim?

Jim Green: Oh yeah. Mary was exactly right. As I said, given the right circumstances, I want our missions to make progress. I don't want to go back and measure the same thing over and over again and stay at a particular level. I'm looking for that next step. And as Mary said, I don't want it oversold either. I don't want us to say, "Hey, we're going to find life." And we're down in level three, and we're going to jump those four levels with this one thing, which would be too daunting a step and it's bound to fail.

Jim Green: I would much rather do it in a very method way that enables us to make progress, recognize that progress, and appreciate what's being done, celebrate that step, and point our attention then to the next things that we need to do. I would hate to also see that discoveries of without this scale, that discoveries of life get threshed around, because we hadn't put it in a context and the public hadn't followed us along the way.

Jim Green: And we spend years threshing around only to say, "Well, oh yeah. I guess we were right." Okay? If we bring everybody along with us and we build that foundation, that next step will be an incredibly important one. One that will be celebrated as probably one of the greatest achievements certainly of this century, maybe of many centuries, and will recognize it when it occurs. That's what we want to do.

Mat Kaplan: Boy, am I with you on that. It is my fondest hope that I am around, that you are around, your co-authors and everybody listening to this is around when we see that confirmed discovery of life elsewhere.

Jim Green: Well, Mary, will probably immediately chime in and say, "Well, Jim Green has always said he will stay at NASA until we discover life beyond Earth. Then, he'll retire."

Mat Kaplan: You better hurry.

Jim Green: So indeed, we better get on it. We better get on it.

Mat Kaplan: I'm going to come back to that in a moment. But as we near the end of our time together, I want to take a slight detour, maybe a couple of slight detours now that I think of it. And Mary, ask you about something else that you have created called NExSS, Nexus for Exoplanet System Science, which is why I came back to talking about finding oxygen in the atmosphere of an exoplanet. What is this about?

Mary Voytek: It was an idea that I got from something that NSF does. They have something called a Research Coordination Network, and it's a way they actually fund groups to do meta-analysis of research and to try to elevate the research that they fund directly. And so, I thought about a system like that really helping us in an area where we had many people from disparate fields in different divisions at NASA, working on a similar problem.

Mary Voytek: And again, I was struck one year by I think four different workshops that were held on habitability and life detection of exoplanets. And it was kind of the same five people that were speaking, but coming from different quarters, the heliophysicists were interested, the astrophysicists, the astrobiologists, and I thought, "We needed some kind of organization to get people together."

Mary Voytek: And so, NExSS is a coordination network that is supported by NASA that brings together researchers that are funded from different divisions that talk about how planets are formed, what makes them habitable? What's the relationship between habitability and what happens on the surface? And what biology could happen? And the star that's in the system that is supporting it. What is the importance of other bodies in the solar system?

Mary Voytek: So it's in a stellar system. If I haven't mentioned this before, I always say, "Everybody is an astrobiologist, they just don't know it yet." And what I mean by that is that in order for us to do this, we need to know everything about what is going on from the establishment of a protoplanetary disc in the formation of the stars and its planets and the evolution of those planets and how we get sources of energy and the whole thing until we finally get to life.

Mary Voytek: And so, NExSS really does that. It brings together biologists that are interested in signatures that we could measure, astrophysicists that are interested in detecting, people that understand planetary dynamics. I establish this with Doug Hudgins in the Astrophysics Division at headquarters, with the support of our division directors, Paul Hertz and Jim Green.

Mary Voytek: And I'm really proud of it. I think that they have started to bring disparate fields together, which is really important. It's not good when people work separately without… Part of our scale actually is calling for you to pay attention to what your other colleagues and other disciplines are doing. I know how to measure oxygen, but do I fully understand what happens to oxygen in an atmosphere? Do I understand atmospheric chemistry? Do I understand what else biology would be doing if it's producing oxygen?

Mary Voytek: You need chemists, you need [inaudible 00:55:10], you need biologists, you need this whole group if you're really going to make progress along this journey. I think NExSS is a wonderful collegial group of excited people with a great passion for understanding exoplanets and the possibility of those that are habitable and those that, not only could support life, but do support life.

Mat Kaplan: Jim, whatever else you may be thinking, I've got to guess two thoughts that might be in your head right now. One, that Mary was a good hire, and two-

Jim Green: Oh she was. Absolutely.

Mat Kaplan: Two, that what we're hearing her describe, and in fact, pretty much all of this conversation is more indication of why people like you are so proud to work for NASA.

Jim Green: Yeah. I agree. I agree. I've had a fabulous career. I've seen so many spectacular things in the field. I'm not an astrobiologist by training. I have tried to enjoy what people are doing, really get caught up of what's happening, understand the science to the best of my ability, and help out any way I can to make it successful. I just really enjoy many different aspects of the science that NASA does and it's just been a fabulous career of doing that. I couldn't have asked for anything better.

Mat Kaplan: And I don't think anybody has been a better cheerleader for the science activity within NASA, including those 12 years that you spent as the head of the Planetary Science Division.

Jim Green: Well, thank you.

Mat Kaplan: You're welcome. If people are detecting an era finality about this, it's because of what we've… The elephant of the room that I've saved for last, which is that we recently learned that you were planning to retire early next year, early in 2022. I'm just hoping that you will come back and do a little bit of a Planetary Radio exit interview and talk with us about what you have seen about what will by then be 42 years with the agency.

Jim Green: Well, my great pleasure. Indeed, it will be for 42 years and I'm planning to draw my attention to a number of loose ends of scientific research and papers that I'd like to finish. I've had the pleasure in my role as chief scientist to be able to not do a lot of the administrative stuff and budget management as I did in Planetary. That frees up some of my time to actually do some scientific research and be part of these fabulous teams and work many different areas and I want to continue doing that.

Jim Green: So my plan is to still stay connected to NASA in some will way. I will tell you this, I have really enjoyed The Planetary Society all the years I was at NASA. And now, I actually can feel good about becoming a member without the conflict of interest.

Mat Kaplan: Well, thank you. Thank you for that. We'll look forward to welcoming you to our own little family. And it's so good to hear that you're going to keep your hand in all the other stuff that's going on there at NASA, because we need you, I think, right, Mary?

Mary Voytek: Absolutely. When I heard the rumor he was retiring, I shot him a message. And it was like, "We had not found life. Where are you going?"

Jim Green: True. She did.

Mary Voytek: Yeah. It would be terrible if you disappeared. We need cheerleaders. We need people who understand and are enthusiastic about what we do. And I echo the work of The Planetary Society. We are in a position to advocate for ourselves always. And we don't always have access to the public in the way we'd like to, to be able to explain things. And I think that your organization has really, and organizations like yours have really done a great job in helping us with that.

Mat Kaplan: Thank you for those unsolicited endorsements. We welcome them. I'm sure-

Mary Voytek: But we don't endorse.

Mat Kaplan: Oh okay. No. Of course not. Of course not. Although, Jim might [crosstalk 00:59:32]-

Mary Voytek: It's a compliment.

Jim Green: Yeah. We'll have to get in the next year. Then, I can endorse.

Mat Kaplan: All right. Let me close with just one more little taste of pop culture, Mary. Because you pointed out that when we realized, Jim, will have spent 42 years at NASA, there's some significance to that number that means something to you and a lot of others out there who enjoy science fiction.

Mary Voytek: Yes. I thought, it didn't make sense to me, but that is the answer. How long are you going to be in service, it's 42 years.

Mat Kaplan: Now, if we can only ask the right question, which is so much of what science is about. Thank you, both. This has been absolutely delightful just as I expected. I look forward to following the progress of this concept as it becomes what I am absolutely sure is going to be a universal or ubiquitous tool that will be very useful in science, and also for those of us who want others to appreciate the PB and J as our boss calls it, the passion, beauty, and joy of the research that you folks do. Again, thank you so much, Jim and Mary.

Mary Voytek: And Jim will be so long and thanks for all the fish.

Mat Kaplan: That's right.

Jim Green: Indeed, thank you so very much, Mat. It was just a delight to talk about these activities and have you relay to the public some of the things that we're thinking about and how we want to communicate and get them as excited as we are, because these discoveries are just unbelievable. And we just have to include everybody in on them.

Mat Kaplan: It's time for what's up on Planetary Radio. Here is the chief scientist of The Planetary Society, it's Dr. Bruce Betts. Welcome again.

Bruce Betts: Thank You, Mat. It is good to be here.

Mat Kaplan: That reminds me of something. I can't quite place that vocalization.

Bruce Betts: Well, that's how I do impressions. I just do a voice and then maybe it sounds like something, and then I claim that that's what I was trying to do. So let me know what I did, and in the meantime, I will tell you about the night sky. You know what is also impressive?

Mat Kaplan: No.

Bruce Betts: If you're going to be in the Southern Atlantic Ocean on December 4th, well, frankly, you're probably there for exactly this reason to watch a total solar eclipse. You can also hang out in this portion of Antarctica and do the same thing. If you're not, if you're in the southern part of some continents down in the southern hemisphere, you may have a shot at it like Africa and South America for partial solar clips. But if not, hey, the Geminid meteor shower is coming up.

Bruce Betts: That will be peaking on December 13th and 14th. If you're in a dark sky spot, you can sometimes see over a hundred meteor per hour, but this year [inaudible 01:02:26] moon will wash out [inaudible 01:02:27] meteors. The good news is it allowed me to say the word give us. He said give us.

Bruce Betts: And other cool stuff, I assume you've been checking it out, Mat. You can't miss it in the evening east, southeast, you've got three planets lined up super bright Venus to the lower right farthest east, and then yellow Saturn, and then Jupiter also looking very bright. And they will keep getting close together over the next few weeks. And the moon loving this alignment will be joining each of them in turn going to Venus on the sixth, Saturn on the seventh, Jupiter on the 8th of December to visit for the upcoming holidays. Making a lovely view.

Mat Kaplan: It's quite a lineup. We've had some dry, clear skies down here in the San Diego area. Not the last couple of nights, it's been foggy, but before that, man, it was just as good as it's going to get in a busy urban area. So I agree with Bruce. Don't miss it.

Bruce Betts: Don't miss it. They're all bright. Saturn is the least, but Venus and Jupiter, brightest starlike objects up there in the night sky. Unto this week in space history. It was 1972 that Apollo 17 launched, something I got to see from a distance in the night launch. It was quite inspirational.

Mat Kaplan: I remember you talking about that. I'm so envious that you got to see a Saturn five leave for the moon. What an experience.

Bruce Betts: Yeah.

Mat Kaplan: But what else is cool? As always [inaudible 01:04:00].

Bruce Betts: Who was that?

Mat Kaplan: It was either WC Fields or there was a walrus cartoon character when I was a kid and it might have been him.

Bruce Betts: Nailed it. We're going to squish some things today, Mat.

Mat Kaplan: Ooh.

Bruce Betts: You're going to love it. If you squished it, you could fit about a thousand of the island of Hawaii inside Pluto's moon Charon. But wait, if you squish Charon, a thousand Charons, you could fit them inside the Earth. You could fit about a thousand Earths inside Jupiter, and you could fit about a thousand Jupiters inside the sun, squishy fun.

Mat Kaplan: Russian nesting dolls of entire worlds. That's just great.

Bruce Betts: We move on to the trivia contest where I asked you what telescope discovered Didymos, the parent body in the binary asteroid system that the Dart mission will be headed to. How do we do, Mat?

Mat Kaplan: Big response. I think I will go directly to Gene Lewin in Washington. You let us know if he got it right with his rhyme this week. With a 0.9 meter eye from a top kit peak, they scammed the sky. On 11 April, what did they see? Didymos 65803, spotted using CCD with suspicions of binary. I love that. Confirmed and dark will arrive there soon impacting with its Didymoon.

Bruce Betts: Wow. That was impressive and correct.

Mat Kaplan: Well, Gene, thank you for the poem. Not our winner though. Our winner, get this, Darren Richie up in Washington, the state of Washington. He said that, "Yeah. Space watch 0.9 meter telescope." More about that telescope in its mirror in moments. Darren has not won for over two years. And the last time he won was when he submitted [Thelonious 01:05:56] in your third order acronym creation contest. Do you remember that?

Bruce Betts: Yes.

Mat Kaplan: It's too long an acronym. We don't have time to go through everything it stands for, but what a… He deserved to win that one. But here's one, he won simply because he was chosen by random.org. So congratulations, Darren. You are going to be getting one of those Planetary Society kick asteroid rubber asteroids.

Mat Kaplan: Now, onto some other stuff. Unless you have more to tell us about the telescope or anything else?

Bruce Betts: No. I'm learning from the listeners.

Mat Kaplan: Here you go. Edwin King in the UK about the telescope having an interesting history. The mirror was actually cast in 1923. First large telescope mirror cast in the US. I remember reading that. And moved up to Kitt Peak in '62, and also in '69, discovered the first optical pulsar and has been used for space watch for a long, long time. Joseph [Putray 01:06:57] in New Jersey said, "Space watch? Well, isn't that what most astronomical telescopes do?"

Mat Kaplan: Yeah. It is, Joseph, but I mean this is looking for the ones that are out to get us, right? Which by the way, I'm going to mention that next week, I will be very happy to welcome, Adam McKay. The writer and director of the new movie, Don't Look Up, and our old friend, Amy Mainzer, who is the science consultant to that film. And I watched it last night. It is wonderful. It is absolutely true. If you'd like at all like satirical, dark comedies, then this is your movie. It's [crosstalk 01:07:38]. Seriously. It has a lot of heart as well.

Mat Kaplan: Kent [Merley 01:07:42] also in Washington. He gave us a whole bunch of stuff that happened before this mirror was cast. Here's one. Light, left, Proxima, [Sentari 01:07:50], that would later arrive to illuminate Walt Disney companies debut of Mickey Mouse all before this happened. Cameron Landers in Texas said that Dimorphos was spotted just eight years later, must have looked lonely, he says.

Mat Kaplan: Finally, from our poet laureate, Day Fairchild, in Kansas. Dimorphos asteroid first was discovered and tagged at the Southwest Kitt Peak where Joseph Montani was using the space watch 0.9 telescope that week. Then, Goldstone delay Doppler echoes were used and confirmed. There's a moon there out back. Now, Dart has been launched in an effort to visit. We're sending Dimorphos some snack.

Bruce Betts: Very impressive poems from the listeners, I must say.

Mat Kaplan: I love them. Thank you, everybody. We do read them all and we sure love your contributions. What do you got for next time?

Bruce Betts: Had something a little different for you, man. I am a mythical creature. What am I? But wait, I will give you one hint. I am also a category of small body objects that orbit between Jupiter and Neptune. What am I? Go to planetary.org/radio contest.

Mat Kaplan: I always knew this about you. You have until December 8th, that's Wednesday. December 8th, 8:00 AM Pacific time. And once again, you have a shot at getting a Planetary Society kick asteroid, rubber asteroid.

Bruce Betts: All right, everybody, go out there and look up in the night sky and think about what your favorite mythological character is. And if it involves a hybrid of Mat Kaplan, thank you and goodnight. Mine does.

Mat Kaplan: Well, I'm glad to hear it, because I know who you're thinking of. And he comes from the planet Krypton, doesn't he? Exoplanet, Krypton. Apparently, a pretty lively place. He's Bruce Betts, the chief scientist of Planetary Society who joins us every week here for what's up.

Mat Kaplan: Planetary Radio is produced by The Planetary Society in Pasadena, California. And is made possible by its members who enjoy life on Earth almost every day. You can support life, the universe, and everything at planetary.org/join. Mark Hilverda and Jason Davis are our associate producers. Josh Doyle, composed our theme, which is arranged and performed by Pieter Schlosser. Ad astra.