Planetary Radio: Space Exploration, Astronomy and Science - A Small, Distant World: Kepler 138b

Episode Date: July 14, 2015

SETI Institute scientist Jason Rowe returns to tell us about the smallest exoplanet so far that has had its size and mass determined. Jason also talks with Mat about our ever-expanding knowledge of these worlds that circle faraway stars.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

It's like Mars, but it's far, far away, this week on Planetary Radio. Welcome to the travel show that takes you to the final frontier. I'm Matt Kaplan of the Planetary Society. We're talking about Kepler-138b and the amazing science that has revealed the size and mass of this little world that is 200 light-years from our home. The SETI Institute's Jason Rowe will give us the lowdown. Bruce Betts will be along shortly to join me for the What's Up segment and your chance to win the space trivia contest. We'll go now to Senior Editor Emily Lakdawalla.

She's not quite 200 light-years away, but she is at the center of the planetary exploration universe this week, the Johns Hopkins Applied Physics Lab in Maryland, where the New Horizons mission is controlled. Emily, first of all, tell us the scene there. Where are you at APL? I am at the Kasiakov Center, which is their education center. It's absolutely buzzing here because they have both the media and the friends and family here. There are hundreds of people around, all equally excited about the approaching flyby of Pluto. Wow. And are they just going to be hanging out there right through the actual flyby? I think they are, and probably a lot more people besides. So it's going to be pandemonium, but a very happy kind of pandemonium. All right. Tell us the latest from New Horizons.

Well, the spacecraft is extremely healthy. Everything is going accordingemonium. All right, tell us the latest from New Horizons. Well, the spacecraft is extremely healthy. Everything is going according to plan. All the downlinks are happening on schedule. All the science seems to be happening. And they even reported some very preliminary science results this morning, which I found very exciting. Oh, can you say anything about those? Probably the one of most interest to listeners is the fact that they finally have pinned down Pluto's diameter with much more precision than we knew it before. And its diameter is 2,370 plus or minus 20 kilometers, which is a very precise number. But more importantly, it happens to be larger than the diameter that we know for Eris, which is 2,336 kilometers.

Take that, Mike Brown. But Eris is still heavier than Pluto. So we have this case where there are these two very similar-sized bodies in the Kuiper Belt that must have had extremely different histories in order for them to end up with such different masses. So it just makes the story more interesting. Now, I have also started to see some speculation about geology, which you were reluctant to do a week ago. How about now? Well, they have their very preliminary first composition results. They're just beginning to be able to tell the pole from the equator with their compositional measurements,

and they have confirmed what they suspected, which is that Pluto does have a polar cap, a cap containing methane and nitrogen ices, and that the equator has actually got a very different composition from the pole. They're detecting much less methane there. So that's just the very first of the results, just a taste of what's to come. Wow. And the images are, as we expected, becoming more and more spectacular. Absolutely, they are. There are so many interesting-looking different kinds of terrain on Pluto's surface. And each image that we get with a few more pixels shows more detail and becomes more exciting. We had a presentation this morning from Paul Schenk, one of the geologists on the team, and he didn't have very much definitive to say about the geology, except that it was really

very different from any other icy world we've seen anywhere in the solar system. Pluto is its own thing. Charon looks perhaps a little bit more like the mid-sized icy satellites of Saturn. We'll have to wait and see what it looks like up close to see which satellite it's most similar to. Emily, I would be even more envious of you if it weren't for the fact that tomorrow evening, as we speak, since some people will be hearing this well after the flyby, tomorrow evening is when we'll be doing our live stream, our live webcast, from Pasadena at 5 p.m. Pacific, 8 p.m. Eastern, and you'll be part of that. I'm very happy to say, reporting to us from APL

as we get the signal from New Horizons. Pretty exciting. I'm going to be bouncing up and down the whole time. So will we. I'm sure our entire live or in-person audience will be doing the same, and our special guests, including Jim Bell, a planetary scientist, Linda Spilker of the Cassini mission, our own Bruce Betts of course, and a surprise killer guest who will not be identified, but there's a good hint in there. Emily, thanks so much. Keep having a great time

and we'll be talking to you soon. It'll be awesome. That's Emily Lochte-Waller, our senior editor. She is at the Applied Physics Lab in Maryland waiting for that big moment when New Horizons makes its closest approach to Pluto and family. And we will talk to her again about that next week. You'll hear it because we'll be presenting highlights of our live webcast just mentioned.

She's also a contributing editor to Sky and Telescope magazine. Joining Emily and speaking to us now from APL, here's the CEO of the Planetary Society, Bill Nye. Bill, you've only just arrived there outside of Baltimore, and it must be very exciting. I told Emily I envy her, and now I envy you as well. Well, it's a heck of a thing. You know, I went to Barbara Mikulski's office as a senator from from Maryland where the Applied Physics Lab is from where this mission is being run. That was back in 2000, went to the launch in 2006. Nine and a half years later, I remember we had these education public outreach growth charts. Get your kid is this tall now, how tall will he or she be in nine and a half years? I mean, it's a long time coming and everybody wonders what Pluto looks

like. Everybody. And so we have these first teasing images, whoa, and this crazy process where the carbon dioxide sublimes and condenses back on the surface and there's methane and there's more ice than people suspected. And this will add to the controversy of Pluto's status, but it will also help resolve it. People can decide if this is a worthy object or not. The big thing is it's round. It's round. And so that right there means it's got a lot of gravity.

I mean, people got to just take a second and think about what it means for something to have so much gravity that it turns into a ball. Like you and I don't do that. Oh, thank goodness. Even really tall people don't do that. When you pick up a rock or you see a boulder, it doesn't turn into a sphere. This is stuff made of the same stuff the Earth is, same stuff you and I are made of, that turns into a sphere from its own gravity.

And it's just influencing those other objects out there just ever so slightly. It's so far away. It's just fascinating. We're going to know so much more about it in the coming weeks. It's exciting, Matt. It certainly is. And Bill, you also will be joining us,

or for some people already did join us, for our special coverage, special Planetary Radio Live on Tuesday evening. You and Emily both. Oh, yes. We'll be there, as the saying goes, with bells on. You'll be there with bells on. We will have Jim Bell sitting on stage with us.

Wait a minute. That's a coincidence. Bruce Betts and Linda Spilker, too, right? Yes, sir. It's going to be very exciting, Matt. You bet. Thanks, Bill. Thank you, Matt. He is the CEO of very exciting, Matt. You bet. Thanks, Bill. Thank you, Matt.

He is the CEO of the Planetary Society out there at APL, the Applied Physics Lab, waiting for the moment we've been waiting for for nine and a half years. The wait is over to speak with Jason Rowe about learning the mass and size of the smallest exoplanet yet. Jason Rolast visited with us in March of 2014. The research scientist works for the SETI Institute in Mountain View, California, but he's also a longtime member of the Kepler science team. On that last visit, he talked about the amazing spacecraft's discovery of many Earth-like exoplanets. Now he's back to talk about one little world, its planetary sisters,

and our ever-increasing knowledge of planets circling other stars in our galaxy, some of which are smaller than our own. Jason, welcome back to Planetary Radio. Thank you. Always glad to be able to call in and chat for a bit. You bet. And we're going to talk about exoplanets again, as we did a little bit more than a year ago. And this was generated by the press release that I received that talked about your role on this team. Tell us about Kepler-138b and what you guys have discovered. Sure. Kepler-138b is one of three planets that are all orbiting the same star. And the exciting part about Kepler-138b, it's the first time we've been able to measure both the mass and the radius for a planet that is smaller than the Earth around a distant star.

Which is really pretty cool. I mean, are you as amazed as we lay people are by how quickly these advances are coming? Yeah, I'm almost speechless when I think about it. When you look at what's happened over the last 20 years and what's happened over even the last five years, mostly spurred by the Kepler observations of how quickly we are learning about extrasolar planets. All right, tell us more about 138b. What does it compare to in our solar system? Is this Mars 2? It has a very similar mass and a very similar radius to Mars.

That means it's about half the size of the Earth and about 5% the mass of the Earth. And that's very similar to what we see for Mars. But this one's a bit closer into its host star. It goes around its host star every 10 days. And it's a cooler M-type star, which means the surface temperatures, equilibrium temperature for this type of planet, is probably on the order of a few hundred degrees Fahrenheit, which means it might be a good place to bake your bread, but not a very good place to live. Not for life as we know it, as we're fond of saying. Gee, that's too bad, especially with all the talk about planets circling red dwarfs

suddenly looking like they might be more attractive places for life. Not here, though, I guess. What about the other two planets in this system? Are they significant? Well, all three, I think, are very important discoveries. So there's 138b, which is the Mars-size, Mars-mass planet, and then there's c and d, which are both about 20% bigger than the Earth, but they have very different masses. c is about twice the mass of the Earth, but they have very different masses. C is about twice the

mass of the Earth, whereas D is about half the mass, which is telling us a lot about the diversity and variety of planets that we're finding around distant stars. The quick takeaway message that we're learning from discoveries such as Kepler-138 is just because you know the radius of the planet, you don't really know much about its composition or even something as simple as its mass. Well, how do you figure out the mass of a planet that we can't even actually see? Sure. So we were able to determine the masses of all three planets by watching them long-term with the Kepler Space Telescope. Able to continuously watching them transit, we were able to see that there were what we call transit timing variations, that sometimes the planet would transit a few

hours early and sometimes about an hour later due to gravitational interactions between all three planets. It's kind of similar to how Neptune was discovered. Astronomers back in the 1800s, such as Herschel, were monitoring planets like Uranus and noting that it wasn't following a purely Keplerian orbit. And from there, they were able to deduce that there was another planet, Neptune, and quickly able to discover it. So it's one of those solar system planets that they say was discovered on paper before it was actually discovered by eye at a telescope. And we use the exact same process of planets gravitationally tugging each other in the Kepler-138 system to be able to deduce their masses. I love this thought that these planets are kind of ratting each other out.

Tell us a little bit about the team. You had institutions from all over involved with this. That's right. We have astronomers at Penn State. The lead author on this one, General Joff Tunter, is our dynamical expert. We had Eric Ford also at Penn State as our statistical expert. Jack Lissauer at NASA Ames, our expert on planet formation. And myself as the expert on Kepler data. So we sort of brought all of our expertise together to help unravel the system. There is something else that came along with this briefing, and it's a YouTube video.

It's an animation that you put together, which, of course, we will put a link up to from this week's show page that people can reach from planetary.org slash radio. It is a wonderful graphical demonstration of how successful we have been in finding out about these exoplanets, not just discovering them, but discovering what their radius is, what their mass is. You put this together, I think, didn't you? That's right. When we were putting together a bit of a press release, we were trying to find a good way to demonstrate just the large variety of both masses and radius that comes with planets. And typically, scientists will plot things on a log-log scale, and that can be a little bit confusing when you look at it the first time. So we decided just to plot it in its pure

numbers in a linear scale to show all the extrasolar planets for which we have both a mass and a radius. So when you watch the animation, we start off by looking at the most massive and largest planets, which are representative in our solar system by both Saturn and Jupiter. And these planets are typically what we call gas giants. Their composition is dominated by hydrogen helium, but there's a lot of it. And that gives them the sizes, which are about 10 times the size of the Earth and about 100 to 300 times as massive as the Earth. And as the animation proceeds, you sort of zoom in towards smaller planets where we meet what are typical of ice giants such as Uranus and Neptune. And now what we're finding around extrasolar planets, which are what we've sort of nicknamed mini Neptunes, which are planets that are a little bit smaller than both Neptune and Uranus, but can have equivalent masses. All these parts of the diagram are well representative. There's lots of

observations that are starting to fill in what is known as the mass-radius relationship. As we zoom in towards Earth and Venus, you'll notice that the discoveries are sort of petering out, mostly because it's very difficult to do. And then finally, you'll go all the way down towards Mars and Mercury, where we have Kepler-138b, which is by far the smallest planet where we have both the mass and the radius measured simultaneously. Not much bigger than Mercury, judging from this chart. No, no. On this scale, Mars and Mercury are not that different. Jason Rowe of the SETI Institute. He'll be back in a minute with more about distant worlds. This is Planetary Radio. one place, Merc? Is that right? Planetary TV. So I can watch them on my television? No.

So wait a minute. Planetary TV's not on TV? That's the best thing about it. They're all going to be online. You can watch them any time you want. Where do I watch Planetary TV then, Merc? Well, you can watch it all at planetary.org slash TV. Random Space Fact! Nothing new about that for you, Planetary Radio fans, right? Wrong! Random Space Fact is now a video series, too. And it's brilliant, isn't it, Matt? I hate to say it, folks, but it really is.

And hilarious. See? Matt would never lie to you, would he? I really wouldn't. A new Random Space Fact video is released each Friday at youtube.com slash planetarysociety. You can subscribe to join our growing community and you'll never miss a fact. Can I go back to my radio now? Welcome back to Planetary Radio.

I'm Matt Kaplan. My guest is Jason Rowe of the SETI Institute and the Kepler Science Team. Jason is a co-author of a recent paper in the journal Nature that provides the diameter and mass of an exoplanet that is about the size of Mars. It's the smallest world ever to be characterized this way. Just before the break, we were also talking about the cool animated chart of exoplanets

that Jason created as part of this work. It's really fascinating, and I applaud all of you for doing this on a linear scale, as you said, and sort of making Earth the unit, right? Because it's all plotted in Earth radii and Earth masses, although you've got the other planets in our solar system here as examples as well. It's really fun to watch it zoom in. I mentioned to you before we started recording, I didn't know if I was imagining it or not, but it looks like there are a couple, at least a couple, of gaps in this graph. Am I right about that? And if I am, what explains it? Some of it is artificial, mostly because we're right now focusing on trying to fill in a lot of firsts, like trying to find smallest planets that are kind of Earth-like. That's the big push right now. there's a lot

of excitement from it i'm particularly excited about it because you're trying to figure out what makes an earth-like planet really earth-like so there's a big push to try to get these small ones which means that a lot of the larger planets are not really getting their observations filled in and then filling in the diagram there's probably a little bit of astrophysics that comes into it, but overall it's just we need to start getting large uniform surveys of masses and radius for lots of exoplanets with a large variety of properties. And that'll help clue in how we actually form planets and what their compositions are. So what is the outlook? I mean, Kepler's still going, right? Now it's the K2 mission.

I think you can tell us about that. But are we going to see new efforts to carry on Kepler's legacy? I think there's many efforts to try to carry on the Kepler legacy. What makes Kepler unique was the very long timescale. It looked at one field of view continuously for four years. Current missions, such as K2, and future missions like TESS, are not going to offer the same sort of observations. When you're using a method such as transit timing variations, where you're watching the planets

tug back and forth on each other, you can really only tease out the properties of masses when you have observations that last for years. So it's going to be difficult with K2 and TESS to sort of get the same level of science. But there is a large push from the community to improve techniques such as radial velocities, which are inherently sensitive to mass measurements, to try to piece together radial velocity measurements, transit timing measurements, to get a wide variety of measurements of planets of different properties. Slowly but surely, we're going to start to fill in that entire diagram. I know that there's work going on, for instance, with the Keck telescope that's already lasted over a decade of trying to pull

out these signals. And now there's the HARPS telescopes that are coming online. They're going to make major contributions towards providing masses for transiting extrasolar planets. providing masses for transiting extrasolar planets. There's no question, though, that the Kepler legacy is going to stand for a long, long time. And I guess a big part of that legacy is that fellow who's responsible for the mission, Bill Berucki, that you've worked with now for years and years. And I just saw the announcement of his retirement. I wonder if you have any thoughts about his contributions and what's next for Bill? Sure. Well, Bill was my supervisor when I first arrived at Ames, and I was very fortunate to be

able to work for him as a postdoctoral fellow. Of course, there is no Kepler without Bill Beruki. He first proposed for Kepler back in the 80s, and he took something like four or six times of applying to NASA to finally get it through. And just recently, he's decided that he wanted to announce his retirement from the civil service to try to spend more time working on Kepler data. So while he's retiring as a member of NASA, he's taking the time in his retirement now to be probably even more scientifically productive by having all the time he wants now to work on Kepler. That is awfully good to hear that he's going to stay in the hunt. You yourself, longtime member of the Kepler team, you're about to make a big change. Where are you headed? Right.

After working with Kepler, I think I've been here for seven years, coming on eight years, is that I've recently accepted a job at the University of Montreal to work on JWST. I'm going to be working specifically on the slitless spectrometer. I'm actually really excited about moving from Kepler, which has opened our eyes about the basic properties and numbers of exoplanets, to going to JWST, which is going to be the workhorse instrument coming up in a couple years for figuring out what makes up the atmospheres of distant rocky worlds. And specifically, can we pull out biomarkers of any signs of life in these distant planets? For example, oxygen?

Oxygen, ozone, water, right? They're going to be very tough, and I'm not going to make promises that we're going to do it, but JWST really does provide our first opportunity to try to do a direct astrobiology experiment, directly searching for life on distant planets. Yeah, I know in October I'm going to start making regular trips down to the Baltimore area to check out the instrument and then start to see the telescope being put together. My job is to characterize the instrument now, so I'm going to be seeing a lot of it. Very exciting stuff. For the two or three listeners to this program who don't recognize that abbreviation, it's the James Webb Space Telescope, of course, and we all have our fingers crossed that it's going to unfold itself and

reveal that huge mirror and then start revealing much more of our solar system, other solar systems, and the cosmos. Jason, it's very exciting to hear that you will be part of that and continuing the search. Thank you again very much for joining us this second round on Planetary Radio. And I wouldn't be surprised if we have you back a third time someday soon. It's exciting science, and it's going to get even more exciting in the future. So I'd be happy to discuss all the new exciting discoveries that are coming up in the near future. Many thanks.

Jason Rowe, he received his Ph.D. for work on measuring the reflectivity of exoplanets. He joined the Kepler team as a NASA postdoctoral fellow, working for Bill Beruki, as you heard. He contributed to the first Kepler discoveries, the hundreds and hundreds of them now. Now he's a research scientist at the SETI Institute, member of the Kepler Science Office, and soon moving back to the Great White North, from whence he came. We will move on to find out what's up in the night sky this week by talking with Bruce Batts in just a moment. Time to talk with another guy who will be or did, if you're listening to this after the Pluto flyby, did join me for our Planetary Radio live coverage of that flyby.

It's Bruce Betts, the Director of Science and Technology for the Planetary Society. Welcome back. Hi, Matt. I will have and had a wonderful time. I'm so glad you will and did. What's up? Still got Jupiter and Venus looking lovely early in the evening west, and they will be joined, especially close to Venus, will be the crescent moon on July 18th. Making for a lovely sight. Venus and Jupiter still getting farther away from each other. Saturn's up in the south in

the early evening. We move on to this week in space history. Appropriately, with the Pluto flyby this week, 50 years ago to the day, was the first successful planetary flyby of Mars by Mariner 4. I remember Alan Stern talking about how we will be celebrating that anniversary with this one. That's very cool. It is indeed. On to Rennan's Baseband. Okay, that's approved.

Thank you. New Horizons. You may have heard of it. It was fueled with plutonium from the RTG unit, the Radioisotope Thermoelectric Generator Unit, that served as a spare for Galileo, Ulysses, and Cassini. They cracked that open, took some plutonium out, and combined it with newly processed fuel sources to make the New Horizons RTG. Okay, so that's been quite a while.

And this kind of plutonium has a fairly short half-life. They made that work, huh? They did indeed. They ended up flying a little less than they had hoped for for various reasons, and got a little less power, but they've made it all work. I guess you never want more plutonium than you need. Well, it's... Planetary spacecraft have never had the luxury of wanting more, or getting more than they wanted. Yeah, yeah. I hope they're working on that. We're helping them work on that. All right, we move on to the trivia contest. And

I said of the names of the moons of Pluto known before New Horizons encounter, which have a family relationship in mythology? How'd we do? Wow, this is very interesting and a good response. And two different answers. What was the one you were looking for? Well, I was looking for Nyx was Sharon's or Karen's mother. Nyx being also the goddess of darkness and night. But some of our listeners said that in those variable Greek myths, there was something else, right? there was something else, right? Indeed, they did. And I'll get to that in a moment. First, though, our winner, and I guess we would have allowed Random.org to pick a winner with either of these answers. Steve happened to come up with one you were looking for, Nix and Sharon, related in mythology, mother of Sharon. That came from Steve Ewer. This is interesting. Steve lives on the island of Samos, the Greek island of Samos off the coast of Turkey.

Steve, you will be, I'm going to guess, the only person in your town on Samos with a Planetary Radio t-shirt. But you never know. You never do. We also got, and this is representative of the other group, from Rachel, Rachel Chu in Melbourne, Australia. She came up with Hydra and Cerberus. Hydra and Cerberus, because there are some Greek myths that say that these two monsters, Cerberus, kind of cute if you like your dogs three-headed, they were siblings. Yeah, I did not know that.

I guess a multi-headed gene worked its way through. It makes some sense as much as anything. Well, thank you, Rachel and others, for that alternative answer. I'm going to just read you one of these funny ones, and not surprisingly from Torsten Zimmer, who often has something humorous for us. He comes up with the ones that you wanted, Nick's and Sharon's. He says that according to an ancient rumor, Sharon's first remark after he got the job of rowing souls across the River Styx was, I'm going to need a bigger boat. What do you got for next time? What was the mass of plutonium flown on New Horizons? Mass of

plutonium flown on New Horizons? Go to planetary.org slash radiocontest. This time you'll have until, oh, let's see, Tuesday the 21st. That would be Tuesday the 21st of July at 8 a.m. Pacific time. We'll definitely give you a Planetary Radio t-shirt. I don't know. If we can, we'll come up with something. Maybe we'll make this a surprise package, bundle something else in there. No promises, but who knows, you might end

up with more than something to keep your top end covered. I'm just gonna leave that. Are we done, Matt? Yes, we are. Thank you very much. All right, everybody, go out there, look up in the night sky, and think about something interesting and when you saw it clearly for the first time. Thank you and good night. I can think of any number of things, but I'm going to go with Saturn the first time I look through a decent telescope. He's an astronomer. He's looked through telescopes. He's Bruce Betts, the Director of Science and Technology for the Planetary Society, who joins us each week here for What's Up? Oh, you lucky people of the future who've already seen New Horizons' close encounter images of Pluto. Oh, well, that's a topic for next week on Planetary Radio,

which is produced by the Planetary Society in Pasadena, California, and is made possible by its members. Daniel Gunn is our associate producer. Josh Doyle created the theme. I'm Matt Kaplan. Clear skies.