Planetary Radio: Space Exploration, Astronomy and Science - A Recipe for a Small Planet

Episode Date: January 20, 2015

Astronomer and planetary scientist Courtney Dressing is the lead author of research that may have found the formula for the mass and composition of Earth-like planets. She reveals the ingredients and why she spent time at JPL while in high school.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

A Recipe for a Small Planet, 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. Planetary scientist and astronomer Courtney Dressing and her co-authors may have discovered the standard ingredients and the masses of Earth-like planets across the galaxy. She'll share her recipe with us today. Was a Chinese astronomer the first to see a Galilean moon nearly 2,000 years before Galileo found it?

Bruce Betts will join me for a surprisingly revealing What's Up segment. First up, our senior editor, Emily Lakdawalla, followed by Planetary Society CEO, Bill Nye the Science Guy. Welcome back, Emily. Why do we find you sitting in a rental car outside of Dulles Airport? That's right. I'm here to attend the New Horizons science team meeting. It's getting so close to encounter time for New Horizons. They're going to start taking science data this month. So it's time for a science team meeting to talk about the plans and to figure out what's next and to try to contain our excitement.

So here we are about to visit Pluto for the first time in the history of humanity. Ten years ago was another first, and you were there. I was there in Darmstadt, Germany, which is where I was for the Philae landing with Rosetta. But ten years ago, I was there for the landing of Huygens on Titan. That was one of the best experiences of my professional career. It's going to be hard to top. This is a great story in the blog. It's a wonderful recap of Huygens landing on Titan, that mysterious moon of Saturn, somewhat less mysterious now that we've peered through its clouds and actually dropped

down onto its surface. This is a January 15 blog post from Emily and is just chock full of great stuff. In addition to the photos, just your impressions of being there, it reminded me of when I was at JPL for the Viking 1 landing. Was that your first landing, Matt? It really was, yes. Yeah, so I think everybody's first landing is always going to be special, right? I was there in Duxstadt again for Philae, and it was really super cool, but it wasn't nearly as awesome as being there when Huygens went down through Titan's cloud for the first time, and the clouds parted, and we saw this

landscape that was both alien and familiar. It had these channels running across the surface and the round rocks on the surface. And then just the whole drama of getting the images out to the public, which is always kind of a struggle with the European Space Agency. But they did get out eventually, and the amateurs had a party with them, and that was really a great day. Interestingly, you were one of the first people there, at least in the media pool, to see some of these images. That's right, because the images were leaked either intentionally or unintentionally. It's never been cleared to me by somebody at the University of Arizona. And they got out on the internet. And you know, once a picture gets on the internet, it doesn't get off the internet. And they tried to shut down

the leak, but the amateurs had a hold of them and made beautiful panoramas. And yeah, I was there. In fact, I was the one who told Arizona about the leak. Some of those panoramas are here in the blog post. And down at the bottom of the post is a video, a bells and whistles, descent data movie, it's called. Tell us a little bit about what's happening here, because then we're going to listen to some of it. Well, it's sort of a control panel view of all of the information that was coming into Huygens as it was descending.

Huygens is an unusual probe in that it was not expected to survive the landing, so it was gathering all this data and relaying it back to Cassini in real time. And this video gives you a sense of all of the different things it was doing at the same time. And it uses sounds to indicate to you which cameras were snapping and which instruments were taking data. It's pretty cool to watch. You have to watch it several times to appreciate all the information it presents. It is absolutely mesmerizing. And we'll put a link to it up, of course, from the show page that you can reach from planetary.org slash radio.

We'll play a little sample of it as we finish this week's conversation with Emily. Thank you very much, Emily, and we look forward to hearing more about the science that is yet to come from New Horizons. So do I, Matt. She's our senior editor and the planetary evangelist for the Planetary Society, also contributing editor to Sky and Telescope magazine. And here is not exactly the sound of Huygens descending to Titan, but a really fun representation of it. Bill, there are developments on the international front that I think interest you this week. Oh, my goodness, Matt.

The European Space Agency has agreed to set aside funds to put a European astronaut on the Chinese space station. My goodness. I mean, it probably won't happen for quite a while, but still that it's in the pipeline is amazing. So this is going to be a real chin stroker for people at NASA, the traditional space agencies, the older space agencies. Now Europe has got a bridge between the old guard, the people that landed on the moon through the Cold War, and the new exploration efforts from China. It's a seed that may grow into an enormous tree, if I may. Certainly something to keep an eye on, as is the Indian space program.

Yes. Yes. So India's got a rocket that they believe will be big enough to do the job, and they're going to build their own human spacecraft as a capsule. And they're going to put people in space. This is another example where governments or citizens recognize the value of space exploration. Of course, there's the national pride aspect. This fills everybody in India with great pride that they were able to explore space in this way, but also, I guarantee you there'll be technological advancements in India and other parts of South Asia as a result of just working, solving the problems

of putting people in space. It brings people around the world together. So this dream that people have, Matt, like people at the Planetary Society, of engaging the world citizens in exploration of the cosmos is coming to fruition. It just apparently takes decades instead of weeks. But it's happening right now, even as we record. Thank you, Bill. Thank you, Matt. He is the CEO of the Planetary Society, Bill Nye the Science Guy. I first met Courtney Dressing in 2003.

She was still in high school, but she had come to Pasadena as part of a very special program sponsored by the Planetary Society and the Jet Propulsion Lab. Now, 12 years later, she is a fifth-year graduate student at the Harvard-Smithsonian Center for Astrophysics. Courtney is also lead author of a paper just published in the Astrophysical Journal. That's not a place where you'd normally look for a recipe, but that's part of what Courtney's team of researchers just came up with, a recipe for building Earth-like planets

that may be duplicated throughout the Milky Way galaxy. The title, The Mass of Kepler-93b and the Composition of Terrestrial Planets. Courtney, welcome to Planetary Radio, and congratulations on this paper just published. Thanks, Matt. It's great to be here. So what impresses me most, I think, about the work that your team has done and the work of so many others is our increasingly amazing ability to learn about planets that we haven't yet actually seen or gotten a spectrum from. Do you also reflect on that fact? I do. It's amazing how much we can learn without even seeing these planets. And it gives me shivers to think about what we'll be able to do in the future when we actually have images of planets orbiting other stars.

Which hopefully is just a few years away. But in the meantime, we're learning a lot. Tell us first about the remarkable work by your colleague Sarah Ballard at the University of Washington that I suppose kind of made your follow-on effort possible. Right. Sarah, together with a team of researchers, conducted what we call astroseismology. She measured the vibrations of a star in order to figure out exactly how big it was,

how old it was, and that allowed her to constrain the radius of the planet Kepler-93b to within 120 kilometers, or 74 miles. It's incredible. It really is. I think she mentioned that it's like measuring the height of someone who was standing on Jupiter. You would be able to measure the person's height to within three quarters of an inch. Yeah, from here, looking at a person standing on Jupiter, I mean, that is just mind-blowing.

So you took that accuracy, and what did that enable you to do? The big question with small planets is what they're made of. In order to figure that out, we'd like to know the planet's density. Is it rocky and heavy like the Earth, or is it lightweight like styrofoam? We were able to use Sarah's very good radius measurement and combine it with a measurement we made of the mass of the planet in order to infer that Kepler-93b is rocky. So in other words, its composition is much like the world that we know best, our own. Is that correct? That is correct, and I'm pretty excited about that.

We had Earth to go on up until this point, and I suppose if you had to look around our solar system, would Venus be the other best analog? I think so. Venus is larger than Mars is. And in terms of its bulk composition, the overall fractions of iron and silicates like rock, Venus is more similar to the Earth than, say, Mercury is. But outside of our solar system, we didn't know until very recently that there's a whole class of planets that seem to have similar composition. Tell us a little bit more about Kepler-93b, which has come up before on this program because it is such an interesting find in our galaxy. Kepler-93b is a small planet. It's about one and a half times the size of the Earth. And it's very, very hot. I would definitely advise against

ever moving there. You would melt. And we now know that its mass is about four times the mass of the Earth. So you combine those two numbers, you get a density of about seven grams per centimeter cubed, which is consistent with an Earth-like composition. So it's a rock. It's a very, very hot rock, but it's still a rock. And there is, in the press release that led to our conversation today, a recipe that we're going to come back to in a couple of minutes. But first, would you say something about how you were able to come up with the mass of this incredibly distant object? We used a technique known as the Doppler wobble.

As a planet orbits around the star, the planet tugs on the star a little bit. So at some points, the star is moving towards you on the Earth where you're sitting with your telescope, and at other times, the star is moving away. Just as an ambulance changes pitch as it drives by, the light from the star changes color. As the star moves towards you, it looks blue. As the star moves away from you, it looks red.

We measured how much bluer and how much redder the light became in order to figure out the mass of Kepler-93b. And came up with what appears to be a proportion that is very similar to Earth's, you said. It's about one and a half times Earth's diameter, but roughly four times the mass of Earth? Exactly. And we did all of that using the HARPS North Spectrograph on the Italian National Telescope Galileo. And that HARPS instrument, that has also come up before on this program. Tell us something about this truly amazing device. Right. The HARPS North Spectrograph is the younger sibling of the HARPS Spectrograph, which is in the southern hemisphere. Both of those are incredible instruments.

They are extremely precise, and they enable scientists to conduct very accurate measurements of the masses of planets orbiting distant stars. They're both very stabilized, so they're temperature-controlled, they're vacuum-sealed, they're isolated. They are incredibly precise instruments. And it's your advisor there at the Harvard-Smithsonian Center who sort of directs the science for Harps North? Right. My advisor, Dave Charbonneau, is in charge of the Harps North science team.

So he works together with people like Francesco Pepe, the instrument designer, to come up with a plan for how to optimize our observations to better understand the masses and compositions of small planets. All right, so this finding began with Kepler-93b. Were you then able to extend this out to the handful of other planets we've discovered that are not too far from the size of our own? That's exactly what we did. We looked at a set of five planets orbiting other stars for which we had very tight constraints on both the mass and

the radius. And three of those planets were ones that we'd studied in detail with HARPS North. We then figured out that if we used models developed by Li Zhang, another graduate student at Harvard, we can find a single model that explains all five of those exoplanets. That model is the same model we would use to describe the Earth. I assume that this means that, of course, you always need more data. But if we extrapolate out, then we're going to find planets that look like Earth, perhaps all over the galaxy. I sure hope so. I think there are a couple open questions. And one of them is, how big can planets get and still obey this relation? It looks like once you get a planet that's bigger than about 1.6 Earth radii, it's not made from the same recipe anymore.

That's astronomer and planetary scientist Courtney Dressing. She'll be back after the break with her recipe for Earth 2.0. This is Planetary Radio. Hi, Mary. Can I borrow a couple of eggs? Sure, Marge. I'll get them from the fridge. Oh, darn. Look at this mess. All my refrigerator magnets have clumped together again. Mary, you need magnetic monopole refrigerator magnets from the Roswell Wonder Company. They're guaranteed to never clump.

Gee, thanks, Marge. I'll order my magnetic monopole refrigerator magnets today. The Roswell Wonder Company. Putting alien technology to work for you. Not an actual company. 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 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 planetary society. 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. Courtney Dressing and her team of scientists have found a relationship between the mass and the diameter of exoplanets that are close to the Earth in size.

It means that these worlds orbiting other stars may be strikingly similar to Earth in their compositions, so much so that she has come up with a recipe for a small planet that she'll share with us in a few minutes. Courtney was telling us more about this almost magical proportion before the break. I wondered if there are other factors that affect the ingredients for Earth 2.0. Does it matter how far that planet is from its star? It might. That's another really important question. So far, because these measurements are difficult to make, we've focused on planets that are very close to their star

because those planets are easier to study. It would be wonderful to know whether these planets are rocky because they never had puffy atmospheres or if they're rocky because they started out puffy, like Neptune, and then that atmosphere was evaporated away by the star. In order to figure out the answer to that question, we need to study planets that are a bit farther from the star as well. How far off are we from having the instruments, the tools to be able to do that?

I think we're just about there. Some members of our team are actually conducting a long-term study to measure the masses of planets that orbit their star once every 60 days or every 100 days. But it requires more data. We could also design bigger and better spectrographs, and some of those will come online too. There's an instrument called G-CLEF, which will be on the Giant Magellan Telescope. I think within the next five years, we will hopefully have the answer to this question of how far away from a star can a planet be and still be a rock. Yeah, the Giant Magellan Telescope, also something that we've talked about on this program.

And it was just last week that we were talking to the program scientist for the European Extremely Large Telescope, which will also be doing exoplanet discovery work. Do you have your recipe that appeared in the press release for making one small Earth-like planet. Is it there in front of you? I'm going to check my cookbook for you. Please do. The Planetary Cookbook. I like that. I have it, and I hope your kitchen's well-stocked. Okay, take us through. What are the ingredients we need?

So first, I'd like you to get out a big mixing bowl and mix together one cup of magnesium, one cup of silicon, two cups iron, and two cups oxygen. Now, mix it well, but don't overmix it. And then go to your spice cabinet and add half a teaspoon aluminum, half a teaspoon nickel, half a teaspoon calcium, and a quarter teaspoon sulfur. Finally, mix all of that together again, shape it into a round ball, and place it neatly in the habitable zone around a star of your choice. It sounds like a very dry mix. How do we get any moisture into this? Well, you have to be patient. It's going to bake for a couple million years. Let it cool. The crust is going to change

color. It might crack a bit. You might see some canyons like the Grand Canyon here on Earth. And then you're going to season it with a pinch of water delivered by asteroids. Now, if we leave this out, it may spoil a little bit. It may get, you know, develop some mold or something. Well, of course, that would be in a real kitchen. What might you hope we would see if this thing is left out for a while? Well, mold would be great, because that could be the thin frosting of life on the surface of your new world. That's exactly where I was hoping you were headed. So what you've done, basically, at least the proportions, are what you found on Kepler-93b and these other planets, The proportions are what you found on Kepler-93b and these other planets, but also on our own lovely Earth.

Exactly. This is absolutely thrilling research. It does seem to be another piece of filling in, ever so slowly, the famous Drake equation from Frank Drake about where we are likely to find life in the galaxy. I think so, and it's exciting to be in grad school at a time where we're starting to discover so many small planets and really starting to understand their properties. Where is your research going next? The next thing I'd like to do is to try to find planets

that are orbiting bright stars and measure the masses of a larger sample of planets. Right now we have seven planets with mass and radius measurements to better than 20% precision. But in order to really understand whether most small planets are rocky and how far away from a star a planet can be and still be rocky, it would be wonderful to have a sample of 100 or maybe even 200 of these planets. So I'd like to discover more planets with the Transiting Exoplanet Survey Satellite

and follow them up in detail. And Courtney, with any luck, you've got a long career ahead of you and plenty of time to see some of these developments take place. Listen, you know that just selfishly here on behalf of the Planetary Society, I have to bring you into your past. Once upon a time, you were in a Planetary Society and JPL program for high school students that made you a student astronaut. First of all, have you forgiven us for not actually sending you into space? I get asked all the time if I've been to space, and it always saddens me to say no, but I forgive you.

Thank you. But that experience, which did have you at JPL, you know, working with real scientists, remind us, what was that program about? It was the Red Rover Goes to Mars program. I felt incredibly lucky to be in the room when the Spirit rover landed on Mars. And I will forever be grateful to the Planetary Society for giving me that opportunity.

We are also extremely proud of you and the other young people who've gone into this field and are beginning to make a name for themselves, as Courtney, you obviously are, with this paper. And once again, I want to congratulate you on it, and I look forward to hearing more as we get better and better about learning about exoplanets and what they're made of and leading up to that ultimate discovery of finding life elsewhere in the galaxy. Thanks, Matt. Astronomer and planetary scientist Courtney Dressing is a fifth-year graduate student at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, where her work is supported by a grant from the National Science

Foundation. Her graduate advisor, we already mentioned him, David Charbonneau, he heads the HARPS North Science Team, that incredibly accurate spectrograph, which was the beginning of this work that led to Courtney and her team's findings. Time for What's Up on Planetary Radio. Here is Bruce Betts, the Director of Science and Technology for the Planetary Society, ready to once again help us celebrate the sky. Hi. Hi.

We have some great, fun, interesting things in the sky, including that comet, Comet Lovejoy. It is around its brightest right now. I went out and saw it last week a few times. You can go out with binoculars and find it over in the general area of Orion and more specifically near the Pleiades. You'll want to look up a finder chart online. If you're in a really really dark site it might be naked eye but probably you're going to want to pull out the binoculars and look for a fuzzy blob, and that will be Comet Lovejoy. I even took some pictures using just my DLSR camera. They're not spectacular, but they do show the greenish glow. Gotten a few of those from some listeners as well, and it's pretty cool.

I was almost out with the binoculars last night, didn't quite make it. Maybe tonight. We've also got just a plethora of planets. We've got in the evening sky Venus super bright, low in the west shortly after sunset. And Mercury, if you catch it early in the week, is over to the right of Venus, much dimmer. Take heart. Jupiter's coming up on the opposite side of the sky in the east around 7 p.m. now, looking super bright. And Saturn coming up late in the middle of the night and over in the sky in the east around 7 p.m. now looking super bright and Saturn

coming up late in the middle of the night and over in the east in the pre-dawn. So we got all the planets you can see with just your eyes up at one point or another during the night this week. You can also catch a lovely sight on the evening of the Thursday the 22nd when the moon jumps in to all of this and is near Venus. Party on to this week in space history. It was 2006 that New Horizons spacecraft launched on its way to Pluto, and we're starting to see more and more Pluto from New Horizons as it approaches for its July close encounter. Lots of exciting stuff coming up. 2004 Opportunity landed on Mars, still giving us great data for Mars. On to... Four Opportunity landed on Mars, still giving us great data from Mars.

On to... Random Space Bug. Excuse you. Excuse me. So I'm not a big fan of the terminology debates in dwarf planets and the like, because I think objects are interesting, whatever. But it works nicely to illustrate a point that all currently recognized dwarf planets by the IAU, of which there are five, the four trans-Neptunian objects, ones out past Neptune, are significantly larger than Ceres, the largest asteroid, which also has cool images coming down from Dawn now.

Yeah, yeah. So Ceres, Pluto, Haumea, Makemake, and Eris. I use it to illustrate a point that there's some pretty darn big objects out there past Neptune and bigger than Ceres, Pluto, Haumea, Makemake, and Eris. I use it to illustrate a point that there's some pretty darn big objects out there past Neptune, and bigger than Ceres, the largest asteroid. I was just reading last week that there may be even more to come, some indications. So stay tuned. Yeah, we'll definitely be finding more. I personally am looking, using my camera.

I will not succeed, because they're really far away. All right, on to the trivia contest. Never say never. Okay. All right, I asked you, besides Galileo, who is the first person to discover a moon around another planet besides Earth? How'd we do, Matt? Wow, such a straightforward

question, and we got some very interesting answers. Let's get the winner out of the way first. I'm pretty sure this is what you were looking for. It came to us from Leonard Sojka in Troy, Virginia. He said Christian Huygens discovered Titan in 1655, 45 years after Galileo found those other moons that got named after him. Indeed he do. Leonard, congratulations. We are going to send you another of those 200-point itelescope.net accounts, itelescope.net, the nonprofit with a network of telescopes all over this planet,

and that's worth about $200. And you can point those telescopes where you like, snap some images, maybe find that dwarf planet waiting out there, that trans-Neptunian dwarf planet. But don't count on it. Yeah, and send us a picture if you do, though. Before we go on to some of the other interesting answers we got, a little bit more detail came from Martin Hajavsky in Houston. He said that Huygens also sketched the Orion Nebula. He was the first to do that. He said Saturn's rings were indeed rings and postulated on solar system habitable zones based on, guess what, liquid water.

But Huygens never paid for anyone else at lunch, insisted, always on going, yes, Dutch. Yeah, yeah. But he was a pretty brilliant dude. Had you ever heard of Simon Marius, German astronomer? No, I'd heard of Simon Marius, the Roman centurion who had a comedy show. Is that right? Was that on the Roman equivalent of Comedy Central? Yes, turn your dial to SBQR. According to Peter Knopf and a whole bunch of other people, Simon also discovered the moons of Jupiter, maybe during the same year the Galileo did, 1610.

Did it all independently. But we also got, this is really interesting, and I had to look this up as well, from Gergely Kovacs in Hungary. this up as well from gergay kovacs in hungary he wrote in to tell us about a chinese astronomer named if i have this correct conte kanye no no no no no not kanye conte this was in the you know astronomers named kanye can only see things in the summer of 365 BC with the naked eye, because, you know, they didn't have telescopes back then, in case you were wondering. That's kind of in question. You know, I had also included that question about who discovered Earth's moon. You said that's not what we're looking for, but I said you could get extra points.

Well, Torsten Zimmer in Germany said, hey, that was Moonwatcher. Anybody remember the ape in 2001 who used to stare up at the moon? Well, if you read the book, you learn his name was Moonwatcher. I think we're ready for another question. Thank goodness. Of the five currently IAU-recognized dwarf planets, which has the longest orbital period, the longest year, and what is that orbital period? Go to planetary.org slash radio contest. Hmm. Okay. You have this time until the 27th of this month, January 27, at 8 a.m. Pacific time to get us the answer. And I think we've finished another one. All right, everybody go out there and look up at the night sky and think about banjos. Thank you. Good night. Five string or four string? Five string. Oh, good. Of course. He's Bruce Betts playing us out of another What's Up here at the end of Planetary Radio. He's the Director of Science and Technology for the Planetary Society. What do you say to making a snazzy Planetary Radio t-shirt the Space Trivia Contest Prize once again?

Okay, you got it. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by the Earth-loving members of the Society. Our theme was created by Josh Doyle. I'm Matt Kaplan. Clear skies.