Enceladus Up Close, with Carolyn Porco - StarTalk All-Stars

Is the subsurface ocean on Saturn’s moon Enceladus the most likely place in our solar system to harbor life? Dive in with StarTalk All-Stars host and planetary scientist Carolyn Porco, guest NASA astrobiologist Chris McKay, and co-host Chuck Nice.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

  This is StarTalk.

• 0:09Carolyn Porco?

  Hello, this is StarTalk All-Stars Edition. I'm your All-Star host this evening. Carolyn Porco is my name, and I'm a planetary scientist and the leader of the Imaging Science Team on the Cassini mission, which is, as we speak, in orbit around Saturn. My co-host today is Chuck Nice. Thank you, Chuck, for being here.

• 0:29Chuck Nice?

  Thank you.

• 0:30Carolyn Porco?

  And my guest today is Chris McKay from the Ames Research Center in the Bay Area. He's astrobiologist extraordinaire. Chris spends his time scouring the deserts of Earth from Antarctica to Siberia, Namibia, Sahara, trying to understand those places on the Earth that might be like Mars in their environment, and wondering how life can thrive there. He's been involved in conjuring what kind of human mission back to Mars might be like. This is a mission that would be piloted by humans. He's involved in that. And I've invited him here today because he is my cohort for the last 11 years in trying

• 1:13Carolyn Porco?

  to get people to pay attention to what we have found with the Cassini mission on Enceladus, which is a small moon in the Saturn system, no bigger across than England, and why this small moon presents to us the most promising environment in the solar system to actually search for life or evidence of prebiotic chemistry. So, welcome, Chris.

• 1:37Speaker 03

  Thank you, Carolyn. It's a pleasure to be here talking with you.

• 1:39Carolyn Porco?

  Yes, so we've gathered your cosmic queries about Enceladus and astrobiology from various social media. That's right, Chuck. Haven't we done that?

• 1:48Chuck Nice?

  Yes, that's exactly what we have done. And we have questions via Facebook and Twitter and you name it, whether it's StarTalk.net, it doesn't make a difference. We take them. And they all want to know about Enceladus and more, you know, astrobiology and more. You know, people see your name and, you know, some people just want to know about Cassini and some people want to know about Saturn. And so I know that we're kind of focused on Enceladus, but, you know, when you say, when people who follow us, when we say Carolyn Porco, they immediately...

• 2:22Chuck Nice?

  Think Saturn because Neil calls you Madame Saturn.

• 2:25Carolyn Porco?

  I'm Madame Saturn. For the rest of my life, I'll be Madame Saturn. It's all right. It could be, it could be worse.

• 2:31Chuck Nice?

  It could be a lot worse.

• 2:31Carolyn Porco?

  It could be worse.

• 2:34Chuck Nice?

  So, uh, let's take our first, you know, we always like to have a Patreon for those of you who are interested in supporting us on Patreon. By doing so, uh, you get to do cool things like, uh, you get invited to parties that we might throw, or you can submit a question, uh, for our cosmic queries and we will make sure that we read it because you gave us money.

• 2:55Carolyn Porco?

  That's a basic transaction in life.

• 2:57Chuck Nice?

  Right? That's a basic life transaction. You gave us money and now we're gonna do something for you. So, um, this is from, uh, uh, Luna McIntyre, who says, um, "Do you think there are parallels that can be inferred by whatever is found with the Europa mission? Since the liquid oceans on both moons," I suppose both moons, she means Enceladus and Europa,

• 3:27Chuck Nice?

  uh, "seems to be due to tidal heating." Um, so are there any, uh, first of all, is that the case? I mean, are both moons, uh, uh, are there oceans created by tidal heating? And, uh, are there any parallels that we can, uh, draw or infer from, um, the similarities between Europa and Enceladus?

• 3:48Carolyn Porco?

  There are a tremendous amount of parallels that we can draw. They are in fact both heated by this mechanism of tidal flexure, uh, which is why they, um, have oceans within them and both of them have oceans. Uh, and I would say it goes the other way, that we have been nearly a dozen years now exploring up close and personal Enceladus with the Cassini mission and, um, with this amazing suite of 12 investigations on the orbiter that have been brought to bear, uh, over the course of those dozen years. And we know a tremendous amount about Enceladus, really far more knowledge about Enceladus at this point in time than we do about, uh, Europa. But I'll turn this over to Chris because Chris also

• 4:33Carolyn Porco?

  has a lot to say about this topic. So what do you have to say?

• 4:36Speaker 03

  Well, to me, the most interesting comparison between Enceladus and Europa would be comparing the type of life we might find in both of them. Imagine sometime in the future, when we find life on Enceladus, we find life on Europa. Are they the same life? Do they represent a common origin? Or did life start independently on both of these water worlds? Or did life start on one and not the other? So I'm always focused on the biology questions. And a comparison between worlds is the most interesting possibility in terms of what kind of questions we can ask about biology and compare these two water worlds. And then, of course, we'd want to compare them to Earth as well.

• 5:17Speaker 03

  I'd ask the biology on Europa, if there is any, and the biology on Enceladus, if there is any, compared to the biology we have here on Earth. That's the ultimate question for astrobiology.

• 5:28Carolyn Porco?

  Yeah. And let me just remind people that why we've gone so goo-goo-gaga over Enceladus.

• 5:36Speaker 03

  Yes.

• 5:37Carolyn Porco?

  And that is because we found that it has 101 tall geysers that are erupting from its south polar terrain, which is an area, if you were to scale Enceladus up to the size of the Earth, it would be like the latitude of Tierra del Fuego and everything south.

• 5:55Speaker 03

  Wow.

• 5:56Carolyn Porco?

  Or if you were biased towards the northern hemisphere, it would be like Edinburgh, Scotland, and everything north.

• 6:02Speaker 03

  Wow.

• 6:03Carolyn Porco?

  So imagine having 101 enormous geysers erupting from the terrain that's that large. And once we found with Cassini these geysers, and we knew that the particles that we see in our images were accompanied by vapor.

• 6:19Speaker 03

  Right.

• 6:20Carolyn Porco?

  And they formed this enormous plume that went ultimately tens of thousands of kilometers into orbit around Saturn. We took Cassini and we went barreling through it.

• 6:31Speaker 03

  Right.

• 6:32Carolyn Porco?

  We went barreling through it time and time and time again. And we've been able to collect material and measure the contents of the vapor, measure the contents of the particles, measure the characteristics of the particles, how big they are, how their size is distributed above the surface. And all this information has finally told us where we are right now. We know we have a global ocean under about thirty-five kilometers worth of ice. It's salty. It's salty, like the earth's ocean is salty and it has organic materials. So it's got all the formal requirements of what in the NASA world, the NASA universe, we call a habitable zone. And that ocean is

• 7:16Carolyn Porco?

  accessible now. What we have to do is fly through it again with the proper instruments.

• 7:21Chuck Nice?

  Right.

• 7:22Carolyn Porco?

  Better than we have on Cassini to measure it with a greater precision and start asking really interesting astrobiological questions. Chris, what are some of the things we could do if we had a mission that went back to Enceladus with proper instrumentation? What kinds of questions do we really want to know?

• 7:45Speaker 03

  Well, I think you said it well, Carolyn. We already know it's habitable. We already know it has organic material. We already know it has liquid water. We know that that liquid water is habitable. So the follow-on questions really go right to the biology. Does this habitable environment, is it inhabited? Does it have life? And then the challenge is, how do we search for life? Well, we can search for life using molecules and tools that we developed for characterizing Earth life, but it'd be nice to also have a capability to detect life if it's not Earth life. So then the question becomes, how do we detect life that's similar to Earth, lives in water, made of carbon, but is not directly related

• 8:25Speaker 03

  to us, doesn't have our DNA? And I think the answer to that is to search for amino acids and search for their handedness and see if there is an enrichment of heavy, complex amino acids in the plume of Enceladus. And then to see if those amino acids all have the same handedness, which is a clear signature of biological selectivity.

• 8:49Chuck Nice?

  So when you, you know, from an astrobiological standpoint, what would be

• 8:56Chuck Nice?

  What would be more desirable? To analyze these things, or analyze these components flying through these plumes? Or capturing the water and bringing it back?

• 9:09Carolyn Porco?

  Good question. That's a very, very good question. There is, there are people out there, groups of people, one group I know of that are looking at the possibility of a sample return. It's not a trivial thing to do, because there's a lot of concern if you bring a sample back to Earth. You don't want to have an Andromeda strain scenario where you contaminate

• 9:30Chuck Nice?

  Yes.

• 9:31Carolyn Porco?

  Earth, so, you know, that has to be done carefully, but...

• 9:34Chuck Nice?

  Those Earthlings were really something special until they bought back that old Enceladus water.

• 9:40Carolyn Porco?

  Really? That was the beginning of the end. You know, the instruments that we have on Earth are far more sophisticated than the ones that we could carry on a spacecraft, so, so Chris, in fact, has been a big proponent of a sample return mission. Yeah.

• 9:55Speaker 03

  But as Carolyn points out, one has to be extremely careful in bringing back a sample from an environment that we think could have life in it, and that environment is very similar to Earth's oceans. We've never done that before. We've brought back samples before, but we've never brought back a sample from a habitable environment. So this is a new challenge, and we have to proceed extremely carefully with it. So I think realistically, the next missions to Enceladus will not be sample return. They will investigate the plume in Situ, following up on Cassini, but they will be designed to search for life, unlike Cassini. Cassini did a fabulous job. It was a wonderful, an unexpected find, and its ability to investigate it surprised

• 10:40Speaker 03

  all of us. And what it told us also surprised all of us. Now we're back with a mission that's based on what we know and search for life in the plume.

• 10:51Chuck Nice?

  And then meanwhile, think about how we bring a sample back safely because ultimately we have to do that.

• 10:56Carolyn Porco?

  Yeah, I wanted, can I just make a plug for Cassini because as Chris said, the instruments on Cassini that were really, I mean, the cameras, you know, can take a picture of anything, but the instruments that told us about the chemistry were not designed to investigate a plume of material that was as tenuous as that which is coming off the south pole of Enceladus. They were designed to measure the atmosphere of Titan, for example.

• 11:22Chuck Nice?

  Okay.

• 11:23Carolyn Porco?

  Which is much more hefty. So it just, it was a beautiful demonstration of how important it is to first of all be in orbit and kind of take up residence in a planetary system so you have the leisure of discovering something and then going back to investigate it again and again and making changes in your approach.

• 11:43Chuck Nice?

  Right.

• 11:44Carolyn Porco?

  And that's what we did with Cassini. But I want to add just one more thing about Enceladus which fascinates me. Ninety-two, ninety-four percent of the stuff that's being erupted from the south pole of Enceladus, the particles, not the vapor, but the particles, comes back down to the surface.

• 12:03Chuck Nice?

  Right.

• 12:04Carolyn Porco?

  It snows back down to the surface. So if there are microbes in the ocean of Enceladus that are being, you know, shot out, they are, it's snowing microbes at the south pole of Enceladus. So I think another thing we want to do is we want to go sample those particles and see if there are microbes in it. That's what I get really excited about.

• 12:21Chuck Nice?

  That's pretty cool.

• 12:23Carolyn Porco?

  It doesn't get any cooler than that.

• 12:25Chuck Nice?

  Yeah, that's, that's like, that's a, that's a holy grail. That's pretty fun. Now, and what do you do when you do that? Is that, is that putting instrumentation down on the surface?

• 12:34Carolyn Porco?

  Well, this is very interesting. You know, we've all been discussing this. We're discussing how you might actually do this. And it just occurred to me recently, you don't need to land on the surface.

• 12:44Chuck Nice?

  Okay.

• 12:45Carolyn Porco?

  All you need to do is really get into orbit around Enceladus and the speed with which you pick up these particles would be gentle enough. That you would not destroy microbes that were in the ice particles. And that's what we want. We'd love to be able to take a look at them. Now, whether or not we have the instrumentation now to do it is a question. Maybe, Chris, do you know something about this? The capabilities of microscopic imagers to do this sort of thing?

• 13:11Speaker 03

  As you point out, we don't have a heritage in planetary missions of searching for life. We haven't done that since Viking, 1976. But meanwhile, NASA and other organizations have been developing technologies for studying life on Earth. There's been satellites in Earth orbit that have looked at biology. There's technologies on the space station. And these life sciences technologies can be applied to the search for life and be made suitable for planetary missions.

• 13:41Chuck Nice?

  Life sciences technology?

• 13:43Carolyn Porco?

  Yeah.

• 13:44Chuck Nice?

  What do you mean by life sciences? That sounds oddly like a life coach.

• 13:51Speaker 03

  Not that. What I mean is...

• 13:55Carolyn Porco?

  Not a lifestyle.

• 13:56Chuck Nice?

  Not a lifestyle. What is the life sciences? Go ahead.

• 14:01Speaker 03

  Well, we can think of two different jobs that we might do in space. One is take life from Earth and study it in space. That's called life sciences.

• 14:09Chuck Nice?

  Okay.

• 14:10Speaker 03

  The other is search for life on other worlds, life detection. They're both centered on life, but in one case, you're taking life with you and studying it. The other case, you're going somewhere and seeing if there's life there. But for example, a fluorescent microscope would be handy in both cases. Well, there's not been the development of such a microscope for planetary, but there has been for life sciences. People have taken these kind of instrumentation into orbit to study organisms that they've carried with them to investigate the response of these organisms to the space environment. You can take that technology and repurpose it to searching for life in the plume of themselves.

• 14:49Carolyn Porco?

  Oh, God, that's so exciting. I can barely stand it.

• 14:53Chuck Nice?

  That is...

• 14:54Carolyn Porco?

  Really. It's like there, it's waiting for us to go back.

• 14:57Chuck Nice?

  Super cool. Super cool. Okay. Let's go on to another question. We have a little bit of time left in our segment, so let's grab another question from Nicole coming to us from Twitter. Uh, @CapeGirl is her name. And she's talking with respect to astrobiology. What role, if any, would the study of planetary atmospheres and remote sensing have on the search for extraterrestrial life? So, is there anything that we can glean just from looking at a planet that we know does not have life on it? And look at the planet's atmosphere?

• 15:42Chuck Nice?

  And I'll go one step further and say even the planet's landscape from, um, uh, from the standpoint of astrobiology and find out about life? Uh, or, or the, uh, or extraterrestrial life on that planet?

• 16:01Carolyn Porco?

  Um, okay. So I think, Chris, this is one for you. Did you, did you get that?

• 16:06Speaker 03

  Yep, I got it. And this is a really good question. It's a really good question. And it has implications right now on searching for life, uh, on a other world, on other stars, exoplanets, and also searching for life on Titan, which is a world that does have an atmosphere and we can't care for. And the thought is that planet, that life does affect the planet and its atmosphere. Here, you had on Earth. The oxygen in our atmosphere is clearly produced by biology. If we see oxygen in the atmosphere of an exoplanet, I would take that as pretty compelling evidence that there is life on that planet making that oxygen. We can apply that same logic. We can't apply that logic to Enceladus.

• 16:50Speaker 03

  It doesn't have an atmosphere, nor does Europa. But Titan does. It's a very different atmosphere than Earth's, would have very different life. But we can take the same logic. If there was life on Titan, how would it change the atmosphere? And the conclusion seems to be it would be depleting hydrogen. So imagine a mission that goes to Titan and searches for a depletion of hydrogen and uses that as a biosignature, the same way that the presence of oxygen in an atmosphere is used as a biosignature.

• 17:19Carolyn Porco?

  Okay, Chris.

• 17:20Speaker 03

  And as your question.

• 17:21Carolyn Porco?

  Chris, we have to, we have to, I'm sorry, we have to take a short break now. We'll come back to what you're saying because it's really exciting and we'll take more of the cosmic queries from our audience when StarTalk returns.

• 17:36Carolyn Porco?

  Welcome back to StarTalk Radio All-Stars Edition. I'm your All-Star host Carolyn Porco and joining me in the studio is Chuck Nice.

• 17:46Chuck Nice?

  Yes.

• 17:47Carolyn Porco?

  Thank you for being here.

• 17:48Chuck Nice?

  Such a pleasure. You're a delight Carolyn.

• 17:51Carolyn Porco?

  Well, thank you. And our special guest is Chris McKay, planetary scientist and astrobiologist extraordinaire at NASA. And he was in the middle of giving us an argument about what you might look at on a planet or a moon that had an atmosphere.

• 18:09Chuck Nice?

  And how that would determine life. And you were talking about if you were to look at an atmosphere and see oxygen, you would know, or you would be able to

• 18:19Carolyn Porco?

  Strongly indicate.

• 18:20Chuck Nice?

  Strongly indicate that, hey, something created that. Something biological created that. So can you go on from there?

• 18:27Speaker 03

  Well, the point was, this is a very powerful technique because it can be done remotely. And the questioner indicated that. And this is true. This is the only way we could detect life currently around planets, around other stars.

• 18:41Carolyn Porco?

  There's some question, now I would just be maybe the devil's advocate here and say that you could never really know to 100% confidence that that kind of a biosignature would give you, would mean life, but it would be a strong indicator, I think.

• 18:57Speaker 03

  That's right. It would certainly be very exciting. Be an Earth-like planet around a Sun-like star and find high level of oxygen in the atmosphere of that planet. Technically, there's other ways, but it would be a strong indication of life.

• 19:11Carolyn Porco?

  Yeah, I know, I know people in that community who think that the only way you'd really know if we had life would be the interception of a signal from an extraterrestrial intelligence. That's like the only thing that would really give you 100% confidence. But, but it would be, it would be a red-letter day if we found an exoplanet with

• 19:29Chuck Nice?

  Oh, that's fantastic. That's, that's good. Well, Nicole, thank you for such a very well thought out question. Let us move on and ask a question from Doug Dumphy, who wants to know, what's the next likely mission to Enceladus? And what do you hope it is capable to do beyond Cassini? Hashtag CQ Enceladus, which is our hashtag. I don't know why I read that.

• 19:59Carolyn Porco?

  Well, you're just, you're just being...

• 20:01Chuck Nice?

  I'm just being thorough.

• 20:02Carolyn Porco?

  You're being thorough, right.

• 20:03Chuck Nice?

  A little too thorough.

• 20:04Carolyn Porco?

  I think we just said that, but we can say it again.

• 20:07Chuck Nice?

  Yes, we did, we did kind of get into that, but go ahead.

• 20:10Carolyn Porco?

  I was just gonna say, Cassini has done a bang-up job unexpectedly because as one of us, Chris, said, I think we didn't really, we suspected Enceladus might have geysers, but we didn't expect that it would, they would be, they would look the way they do and be as vigorous a phenomenon as it has been. It's just been an explorer's dream come true. And so what we want to do next is go back with instrumentation that is far better than that which was carried by Cassini, look at the chemical constituents to a finer level of detail, and look at abundances of compounds, look at, as Chris mentioned,

• 20:53Carolyn Porco?

  the handedness of compounds, because you know, earthly life prefers a particular type of molecule to another. And if we see that same kind of signature on another planet, that might also indicate a process like life that has singled that particular type of molecule out. So those are the kinds of things we would look for. And like I said, one of my favorites is actually to grab and look at and image microbes. So that's the kind of things that we're talking about going back to Enceladus.

• 21:24Chuck Nice?

  Nice. But the key is, we are going back. Is that the key?

• 21:30Carolyn Porco?

  Oh, no, nothing...

• 21:30Chuck Nice?

  What, what do you mean?

• 21:31Carolyn Porco?

  Oh, well...

• 21:32Chuck Nice?

  Why would you say that?

• 21:33Carolyn Porco?

  Well, there's a bunch of us that are really pressing for it, and we have the opportunity, there's, we now can submit to NASA what are called New Frontiers proposals. So this is proposals for like a big chunk of money, something like 850 million dollars. Uh, but that doesn't mean we'll get selected. There are people who want to go to Venus, people who want to go return a sample from a comet. There's lots of competition.

• 21:55Chuck Nice?

  Let me ask you this. I mean, this is, this is just part of our conversation. And I, I, I think it's terrible that we have to kind of, um,

• 22:03Carolyn Porco?

  Make choices?

• 22:03Chuck Nice?

  Choices like this. These Sophie's choices where, you know, it's like, well, should we go to Venus? Or should we go to Mars? Or should we go back to Encel- It's like, we should be doing all of this, to be honest. I mean, Let's, let's be, let's be very square. We should be doing all of this. Um, so how do you prioritize? Which missions should take place and when? Uh, is there a particular protocol that should be in place to determine, uh, maybe this mission is important, uh, but it's more important if we go now. Maybe this mission is important, but it really won't be important until, you know, 2030.

• 22:42Chuck Nice?

  So how do you go about making the case for, you know, getting these limited funds, which shouldn't be limited as far as I'm concerned?

• 22:51Carolyn Porco?

  Well, they are limited. And Chris, I'll let you deal with this. You're the guy who works at NASA.

• 22:56Speaker 03

  Sure, sure. But I, I'll tell you my way of prioritizing these, because I have to prioritize my time also. What do I work on? Uh, all the planets are interesting. I prioritize it based on what's going to tell us the most about biology now. And I think the clear winner is Enceladus. So I would answer, are we going to Enceladus? Yes, because it's clearly the place where we can learn the most about possibility of life right now. Uh, other worlds are interesting too, but Enceladus is ready for investigation. Uh, there's samples there. As Carolyn said, it's a habitable environment. Samples come out into space. It's the low hanging fruit. It's what we ought to do first, in my opinion.

• 23:36Carolyn Porco?

  Yeah, it's not clear. It's, it's not clear it's going to happen, but Chris and I, that's why we're cohorts in this together.

• 23:41Chuck Nice?

  Nice.

• 23:42Carolyn Porco?

  We're trying to keep Enceladus up front and center in the minds of people because, uh, it, it is, like you said, it's, it, we're ready. We're ready now. We know enough to go back and do the job right.

• 23:54Chuck Nice?

  Good stuff. Let's move on and take another, uh, question. Um, this one a little bit more broad from, uh, Kabir, uh, Mal, Malhotra. I'm, I'm, Carolyn, you will know the more you do this.

• 24:10Chuck Nice?

  Uh, people like to, and Chris, you will know, because I'm sure you will return as a guest. Uh, people send me their names and uh.

• 24:18Carolyn Porco?

  You have no idea how to pronounce it.

• 24:20Chuck Nice?

  And I butcher their names like you can't believe. And I think that they're doing it on purpose now.

• 24:25Carolyn Porco?

  (laughing).

• 24:27Chuck Nice?

  I, I, I really do. I think people are just sending me made up names.

• 24:31Carolyn Porco?

  Just to, just to see you.

• 24:32Chuck Nice?

  To see me squirm and struggle and (laugh) because, uh, but anyway.

• 24:39Carolyn Porco?

  At least they're listening.

• 24:40Chuck Nice?

  This is true.

• 24:40Carolyn Porco?

  Okay.

• 24:41Chuck Nice?

  Exactly. So this is, I hope I'm saying Kabir Mahotra. Mahotra. Okay.

• 24:49Chuck Nice?

  Assuming the universe is infinite. That's a big assumption right there. I mean, is the universe infinite? Because I really don't think it is. But anyway, let's not, that's, this is not, I'm not answering these questions. You are. (laughing). How long will it take, uh, to produce

• 25:09Chuck Nice?

  an exact copy of Earth? I don't think he means exact copy of Earth, but an Earth-like planet, just, you know, basically our Earth. So an exact copy is ridiculous because, you know, that's ridiculous to say an exact copy of Earth. That's just never gonna happen. And by the way, the Earth is changing all the time. So what would that exact copy be?

• 25:29Carolyn Porco?

  Right.

• 25:30Chuck Nice?

  You know, because the Earth that we live on today is not the Earth that was here four million years ago.

• 25:35Carolyn Porco?

  That's right.

• 25:35Chuck Nice?

  It's a completely different planet now. So, but how long would it take to produce an Earth planet?

• 25:43Carolyn Porco?

  Well, I would, I'm gonna turn this around because

• 25:45Chuck Nice?

  Okay.

• 25:46Carolyn Porco?

  that's very difficult to answer. So I'm gonna turn it around to something that's possible to answer.

• 25:51Chuck Nice?

  (laughing). I like the way you work.

• 25:54Carolyn Porco?

  The Kepler results of how many exoplanets there are and what characteristics they are. This is Kepler with follow-on Earth-based observations from telescopes like HEC.

• 26:05Carolyn Porco?

  Have indicated something like 25%, I hope I get this right. 25% of the planetary candidates that they find in the habitable zone of their star are Earth-sized.

• 26:20Chuck Nice?

  Oh, okay.

• 26:21Carolyn Porco?

  I think that's right. And then some fraction of those would be Earth-like and you could call it, you know, Earth twin, Earth's twin.

• 26:28Chuck Nice?

  Right.

• 26:29Carolyn Porco?

  And I don't know, someone took a reasonable guess, maybe let's say 20%, you know, it's common. Nothing on our planet is unusual.

• 26:38Chuck Nice?

  Right.

• 26:39Carolyn Porco?

  That's what we've been able to glean about the universe is, you know, what we have here is probably lots of other places.

• 26:45Chuck Nice?

  Right.

• 26:46Carolyn Porco?

  So 25% of the planetary candidates in their habitable zone are like Earth-sized. Let's say 20% of those are Earth-like, which means like the Earth.

• 26:56Chuck Nice?

  Uh huh.

• 26:56Carolyn Porco?

  Okay, the copy. And, and when you go through all the numbers, the last time I heard this, which was probably six months or a year ago, the number came out to something like 5 billion, 4 billion Earth-like planets in our galaxy.

• 27:10Chuck Nice?

  Oh my, that's just here, right now.

• 27:13Carolyn Porco?

  Right, Chris? Do I got that right?

• 27:15Speaker 03

  The gist of the argument is certainly correct. There are gonna be in our own galaxy, a lot of Earth-like planets. We just gotta look. We know that there's lots of planets out there and some of them would be like Earth. We don't need an infinite universe. Our own galaxy, in fact, our own stellar neighborhood probably has lots and lots and lots of Earth-like planets arbitrarily closely similar to Earth. The more we wanna look, the more we can find ones that are as close to Earth as we want it to be.

• 27:43Carolyn Porco?

  Really, we might have a lot of community work ahead of us.

• 27:46Chuck Nice?

  Yeah, wow. So, I mean, that's, that's pretty unnerving when you think about it because, now...

• 27:56Carolyn Porco?

  Unnerving, it's, it's, it's like...

• 27:58Chuck Nice?

  It's just incredible.

• 28:00Carolyn Porco?

  It's incredibly exciting.

• 28:01Chuck Nice?

  It's exciting. When I say unnerving, I mean in a, in a, in a, in a good sense. It is really that exciting that, that it's unnerving. It's, you know, it's, it's shocking, is what it is. It's shocking. So now let me ask the both of you this. With that in mind...

• 28:20Chuck Nice?

  Does it necessarily increase the likelihood of there being intelligent life on one of those planets since we pretty much developed on this planet? Does it increase the likelihood or does it, does it not? I mean, are those two things related in any way scientifically? Or, I mean, you know?

• 28:36Carolyn Porco?

  Well, look, we have, we have a statistic of one. We know on an Earth-like planet, one civilization has developed to the point where we call ourselves intelligent and we are capable of communicating across space. So, you know, if it happened once, it's likely to happen again. How, how likely is it? I don't know. I guess that's a guess, but I, I'm an optimist. I think that probably it's, it's happened many times. Chris, do you want to take a guess? What do you think? You're an optimist, I know.

• 29:08Speaker 03

  I, I am as well, and I, I think it's useful to divide the question into two steps. One is the distribution of life, and then secondly, the distribution of intelligent life. Certainly, we think that life should be widespread. Whether some of those life forms develop intelligence is a more deeper question, but I tend to be an optimist too. So I think we're going to find the universe is full of life and that many, but not all of those life-bearing planets have developed intelligence.

• 29:34Chuck Nice?

  Gotcha.

• 29:35Carolyn Porco?

  That doesn't mean that they're like on their way to get us right now. It's the distances are, I mean, are prohibitive. When you say a star is 12,000 light-years away, that, we're talking, that's the time it takes light.

• 29:50Chuck Nice?

  Right.

• 29:51Carolyn Porco?

  The fastest thing we have to get here. It would take us far, far longer than that, so.

• 29:54Chuck Nice?

  Yeah, so, I mean, the, the, realistically, these, life could exist there, but our being able to get to that life is very unlikely.

• 30:09Carolyn Porco?

  Well, eventually, I suppose we could put, put some robotic spacecraft on a course for some star and maybe...

• 30:17Chuck Nice?

  That makes sense, yeah. Robot, I mean, that's so, so that brings me to another question from both of you. Okay, especially you, Chris, being an astrobiologist. Is it more important to have a first contact? Uh, from one of us making contact with intelligent life. Or from an emissary that we have created, i.e. a robot, or an android, or, you know, some representation of human life, whether it's a computer or what have you. You know, of course, that probably will make more sense because we can send that thing out and just let it go. We don't have to feed it, we don't have to worry about it dying, and it's not going to bitch and complain like I'm lonely and I miss my family. So.

• 31:02Carolyn Porco?

  Yeah.

• 31:04Chuck Nice?

  So, I mean, is that most likely how we're going to make our first contact?

• 31:09Carolyn Porco?

  Uh, you know, we might have made a first contact already.

• 31:12Chuck Nice?

  Ooh.

• 31:13Carolyn Porco?

  You know, I mean, we have our signals sent out. What did Dan Wertheimer just say? He said seventy years ago.

• 31:22Chuck Nice?

  Right.

• 31:23Carolyn Porco?

  Seventy, something like that. But, you know, so, so we won't know. That's the thing about this whole thing, the distances are so huge. We won't know if we've made a contact with another civilization until we hear back from them.

• 31:38Chuck Nice?

  Got you.

• 31:39Carolyn Porco?

  Okay.

• 31:39Chuck Nice?

  Interesting.

• 31:40Carolyn Porco?

  Yes, okay, so, we have just limited time, so, we're going to wrap this up for this segment. We'll take a short break, and when we come back, we're going to entertain more of our listeners' cosmic queries when StarTalk returns. Hello again, and welcome back to StarTalk Radio, All-Stars Edition. I am your All-Star host, Carolyn Porco, and joining me in the studio is my fabulous, wonderful, dynamic co-host Chuck Nice. Thank you.

• 32:16Chuck Nice?

  Thank you. One moment, I started to look around to see who else was here.

• 32:21Carolyn Porco?

  And we have as our special guest, we have Chris McKay, who's an astrobiologist from NASA Ames Research Center in the Bay Area. We've been talking about the search for life in the solar system. There isn't a topic that's more exciting than that, and we're going to now discuss what kind of life... We might find on a place like Enceladus and how might it be different than the life we have here on Earth? This is a really tantalizing question because I think most people would agree it would really be far more interesting to find life that was entirely different from the life we have here biochemically, metabolically, all those things, because then we'd have a

• 33:05Carolyn Porco?

  point of comparison that we could make and that would give us insights into how life developed one way on one planet and one way on the other. So Chris, why don't you weigh in on this for us because I'm sure this is something that you've thought quite a lot of.

• 33:21Speaker 03

  Sure. Normally when we talk about different life, we're thinking something exotic like maybe silicon-based life or something. That's not what we're going to find on Enceladus. Enceladus is a world with water and carbon. Life there will be big carbon, just like us. But it might still be profoundly different. How that carbon and water arranges to form biochemistry could be very different on Enceladus. So for example, DNA, which we use to store information, may not be the same molecule used on Enceladus to store information. The proteins on Enceladus may be made out of amino acids, just like the proteins on Earth, but they may be made out of different amino acids.

• 34:03Speaker 03

  Or the chirality, the handedness of those amino acids might be opposite. So there's many ways that life on Enceladus could be very, very different than life on Earth, and it would be very interesting to do that comparison.

• 34:17Carolyn Porco?

  Now, for us to do that, I'm guessing that that's going to be pretty hard to do with the kind of stuff we're talking about that might be done on the very next mission to Enceladus. I'm going to guess that in order to do that, we really got to bring samples back to Earth. Do you agree with that?

• 34:37Carolyn Porco?

  To really-

• 34:37Speaker 03

  Well, not necessarily. I think-

• 34:39Carolyn Porco?

  Go ahead.

• 34:40Speaker 03

  I think we could go a long way with instruments that we send there. If, for example, we search for amino acids and we find that the plume of Enceladus has amino acids, complex ones, and they're all, let's say, right-handed, the opposite of Earth life, then we've learned an enormous amount about life on Enceladus, and we've determined that there's life there, and it's a separate life from Earth life.

• 35:05Carolyn Porco?

  Uh-huh. Okay, so you're talking about corality or handedness, but what about the way its proteins are structured, or the way, you know, the amino acids go together? That's really higher-order stuff. That's hard to do without bringing a sample back, don't you agree?

• 35:23Speaker 03

  Sure, we won't answer all of our questions. We won't answer all of our questions, but we'll answer-

• 35:29Carolyn Porco?

  Sounds like you've got some life form there, crawling around.

• 35:33Speaker 03

  Yeah.

• 35:36Speaker 03

  We won't answer- If you want us to go.

• 35:39Carolyn Porco?

  Oh, okay.

• 35:41Speaker 03

  We won't answer all of our questions. And more complex questions will require more complex instrumentation. But we will be able to answer some questions. And if there is life there, we have a good chance of determining that it's there and determining that it's alien from Earth life. So we could, in principle, go pretty far down the logic tree. Now, eventually, yes, we do want to bring a sample back to Earth. Eventually, the level of sophistication we'd like to apply to investigating a different type of life is the state of the art. And to do that, you need to bring the sample back. But we can make a lot of progress on the next mission if we send the right instrument.

• 36:18Carolyn Porco?

  Okay, so let me, you know, this is our last segment, and I just wanted to open it up even more, if I could, Chuck. Go ahead, please, please. In the Saturn system, there's another tantalizing place, which is Titan. Titan is considered kind of, believe it or not, we used to think of Venus as the sister planet to Earth, but Titan is even more like Earth in many respects than Venus is. It has landforms that are like- We have here on Earth because it's got a substance in its atmosphere, methane, which acts like water does.

• 36:53Chuck Nice?

  Right.

• 36:54Carolyn Porco?

  Here on Earth, and it rains out of the sky, it can form clouds, it can carve channels and gullies and so on, it can pond on the surface, and in fact, it's doing that. In the polar regions of Titan, we have found seas of liquid methane.

• 37:10Chuck Nice?

  Wow.

• 37:11Carolyn Porco?

  Laced with ethane. So, I mean, think of, you know, Lake Michigan brimming with paint thinner, or something like that.

• 37:18Chuck Nice?

  You know, that's not too far off in the future. If you keep going the way we're going right now.

• 37:23Carolyn Porco?

  So, so, you know, now, I'm not a fan of thinking that we have life in the seas of Titan because, or at least, excuse me, I should say that we have a chance of really recognizing it, because it would be so different than we have here on Earth, because we know about earthly life. But I know Chris is a big fan of this idea, so I wanted to give Chris the opportunity to elaborate on the possibility that we could have life in Titan seas, given that the temperature there is so cold and the kinetics are going to be so slow and so on, and then how we might go about even recognizing life in the Titan seas.

• 38:03Speaker 03

  Well, that's a really good question, and it roots to what do we think life needs? It's clear that life needs a liquid. On Earth, that liquid is water. The only other liquid that's widespread in the solar system is the liquid methane and ethane on Titan. So could life use that liquid? Now, it's very different than water, but that doesn't mean that a bit of life couldn't use it, but it would be so different, we wouldn't really know how to recognize it. And that's where we would, on the effect that life has on its atmosphere, as we talked about earlier, if there's life on Titan, it might be consuming hydrogen, and we might be able to detect that atmospheric effect more readily than

• 38:46Speaker 03

  we could actually detect the life form, because we don't even know what kind of molecules to search for.

• 38:51Carolyn Porco?

  Right.

• 38:51Speaker 03

  It certainly doesn't use amino-

• 38:54Carolyn Porco?

  Yeah, right. It doesn't use amino acid. So it's it's going to be significantly different. It's just a challenge in the space program. It's a challenge to, you know, like I said, this is where the rubber meets the road. You have to design and experiment. You have to know what you're going to measure. And when you're looking at at an environment that's alien to the earth and life that may not even be constructed like the earth, that is no common biochemicals, it becomes very challenging.

• 39:21Chuck Nice?

  Yes, that was fascinating. That was great stuff, great stuff. I mean, I'm I'm still fascinated by just the fact of life living in a methane ocean. That that alone is kind of mind boggling.

• 39:37Carolyn Porco?

  Yeah, well, you know, you know, they say, was it Rudyard Kipling that said travel is mind expanding? Well, you know, planetary exploration is mind blowing.

• 39:45Chuck Nice?

  There you go. All right, let's take a question. Pardon me. I'm terribly sorry. Drew Davenport, and Drew Davenport is writing from Willmet, Illinois, here on planet earth. He actually put it that way.

• 40:01Carolyn Porco?

  Oh, that's good. We want him, yeah.

• 40:05Chuck Nice?

  Have you ever found anything that you couldn't identify or thought was really strange during a spectral analysis? This is for both of you, actually, because I'm sure that spectral analysis is is part of both your missions.

• 40:20Carolyn Porco?

  Oh, major, major. Well.

• 40:22Chuck Nice?

  Now, is there anything that comes back where you're just like, my, that's that's odd? Well, strange?

• 40:29Carolyn Porco?

  Um, I I'm not a spectral analyzer myself, but I remember in the early days of the Cassini mission when we were looking at the results of one of the spectrometers onboard Cassini that had scooped up material in the plume. And there were some signatures that they couldn't make sense of. And I think at first, in fact, they. Made a tentative identification, which did not turn out to be correct, and it turned out to be salt. Yeah. They had, they had not thought that there would be salt. Uh, and when they went back and said, okay, maybe this is salt, and they went back and did the match, it was a great match. So that's my little anecdote. Chris, you must have one.

• 41:10Speaker 03

  I can't think, think of something offhand, but along the lines of, I remember when we were first going to Titan, we thought it had a global ocean. We got there, it didn't. Uh, so that, we were often surprised. I think we have to keep that in mind. We, we, our guesses of what's out there are often wrong.

• 41:28Carolyn Porco?

  Right.

• 41:29Speaker 03

  The only way to know is to go look.

• 41:30Carolyn Porco?

  You know, this brings up something that I love to just remind people of in, in being explorers like we are, you know, we're kind of our, if not our bodies, our minds and our emotions are on these robotic spacecraft that we send across the solar system. And, you know, they find things that are, you know, we say, oh my God, that's so surprising. We felt that way about the Enceladus plume. We felt that way about the distribution of the hydrocarbons on Titan. Uh, we all felt that way about Pluto. When New Horizons got to Pluto, oh my goodness, look at this, these regions where you have ice convection and these polygonal features.

• 42:12Carolyn Porco?

  It's not so much that it's a failure of knowledge, it's a failure of imagination. Hmm. We understand physics pretty well and chemistry. We understand what happens at various regimes, physical regimes, but it's just that we don't spend an infinite amount of time imagining all the various permutations we might find there. Right. And when we get there, we end up being surprised. Like, take the Enceladus geysers. We knew post Voyager, this was after the Voyager mission, a couple of years later, a, a paper was written about the possibility that we could have water geysers on Enceladus. Right. All right. It was suggested that these geysers, they might not have been called geysers, but they

• 42:52Carolyn Porco?

  would be producing particles that would go into orbit around Saturn to produce the E-ring in which Enceladus is centrally embedded. So that was the connection. So we had... Geysers on the brain when we went to back to Enceladus with Cassini. And we even the imaging team planned observations to look for them. And the first image that we have of a plume coming off Enceladus has the word plume in the title of the observation. It was deliberately planned to search for plumes.

• 43:26Chuck Nice?

  Right.

• 43:26Carolyn Porco?

  So we knew what we possibly might find, but nobody took the time to imagine, well, okay, so we have geysers coming off Enceladus. The gravity on Enceladus is only one hundredth of the gravity here on the earth. So these things are going to be enormous. No one thought that.

• 43:42Chuck Nice?

  Right.

• 43:43Carolyn Porco?

  So we get there and we see this incredible spectacle. And it just it it just reminded me of this, that, you know, we we always fail to imagine what we might find. So it and it's what it makes it so thrilling, you know, just seeing something for the first time. It's just it's mind blowing.

• 44:02Chuck Nice?

  That's pretty cool.

• 44:03Carolyn Porco?

  Of course, it's cool.

• 44:04Chuck Nice?

  Excellent, excellent, excellent stuff. All right, let's actually Theron, actually actually Theron and coming to us on Twitter at astrotheron, not to be confused with Charlize.

• 44:18Carolyn Porco?

  Theron.

• 44:21Carolyn Porco?

  Maybe maybe that's a fan of Charlize.

• 44:24Chuck Nice?

  Says, ask this, I really don't understand this question at all, so you guys are going to have to help me. Given similar environmental challenges, i.e. liquids behave the same, is it possible for exobiology to produce a species similar to us?

• 44:45Carolyn Porco?

  We have only about a minute.

• 44:47Chuck Nice?

  Oh, yeah.

• 44:47Carolyn Porco?

  So you're saying, given similar biology, is that the similar chemistry?

• 44:51Chuck Nice?

  Yeah, similar environmental.

• 44:54Chuck Nice?

  Yes.

• 44:55Carolyn Porco?

  Should we expect something similar to us?

• 44:57Chuck Nice?

  Yes. In other words, is that, are we more likely to find something similar to us, given the similar situations or environmental situations? Or, you know,

• 45:07Carolyn Porco?

  I think I-

• 45:08Chuck Nice?

  Should we be using our imagination to look for what you just said?

• 45:11Carolyn Porco?

  Uh, okay. Well, so using your imagination for every permutation would take quite a bit of time. I think this is a question that really devolves to this. What in the evolution of life, what role was played by basic physics and chemical laws? And what was played by serendipity? What was, you know, a meteor hit the earth and destroyed the first experiment, just wiped out all life that was just getting started?

• 45:38Chuck Nice?

  Right.

• 45:38Carolyn Porco?

  Uh, and then, um, giving something else the opportunity to evolve? Like, you know, the dinosaurs being wiped out open up the, the way for us. So we only have seven, six seconds. We're gonna have to wind down now. Chris and Chuck, thank you for helping us out today. It's a pleasure. You've been listening to StarTalk Radio All-Stars Edition. I've been your All-Star host, Carolyn Porco. Until next time.