Planetary Radio: Space Exploration, Astronomy and Science - Billions and Billions of Earthlike Planets?

Episode Date: April 21, 2008

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Billions and billions of Earths? Maybe this week on Planetary Radio. Hi everyone. Welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. There is evidence that many, maybe even most of the stars in our galaxy have rocky planets whirling around them. We'll talk with astronomer Michael Meyer,

who led the international team that found this evidence in dust. Emily Lakdawalla explains why a blue sunset in a red sky is perfectly normal on Mars. And Bruce Batts will join us for a special mobile edition of What's Up with our usual guide to the night sky, a new space trivia contest, and much more. Bill Nye the Science Guy has the week off. He'll be back with a new commentary next time.

Peggy Whitson has come home. The first woman to command the International Space Station and her Russian companions plunked down to Earth in a Soyuz capsule on April 19. That capsule missed its intended landing point by a few hundred kilometers, but all is well. Peggy now holds the record for time spent in space by an American astronaut, 377 days. She got in five spacewalks, too. 377 days. She got in five spacewalks, too.

There are doubters, but a team of scientists at the University of Rome claim to have discovered the theorized particles that might be the essence of dark matter, that mysterious material that appears to make up so much of the universe's mass. They believe that their new and improved detector found weakly interacting massive particles, otherwise known as WIMPs. That still leaves dark energy to be explained. So far, no one has come up with a theoretical force explaining that mystery. When they do, I hope they call it Dweeb.

Speaking of mysteries, Emily Lakdawalla has an update on the Pioneer anomaly in her blog at planetary.org. Slava Turashev and his co-workers at JPL have come up with a partial explanation for the weird acceleration of the old Pioneer 10 spacecraft. Some of it could be caused by uneven heat radiation. But this thermal modeling doesn't provide a full explanation. Next up, Michael Meyer. What if most of the stars in our galaxy have rocky planets, planets like Venus, Mars, and Earth? They might not all be friendly to life as we know it,

but surely some good portion of them would make nice homes. Last month, astronomer Michael Meyer of the University of Arizona and his research colleagues published a paper in the Astrophysical Journal. That paper contained their findings indicating that as many as 60 percent of stars do have rocky planets circling them. Their evidence is not based on seeing these extrasolar or exoplanets, but on the tremendous disks of gas and dust that surround young stars. I found Michael at the Harvard-Smithsonian Center for Astrophysics, where he is on sabbatical. We talked about exoplanets on this program, conversation with your JPL colleague Mark Swain, who found the first organic material on an exoplanet, a planet circling another star. Now there's your research or the research by this international team that you led that says, okay, there are organics and water out there, and maybe there are a lot more rocky planets to find them on than anybody ever thought. Well, that's right. We were using, our team was using the Spitzer Space Telescope to search for the signatures or the signposts of planet formation.

And for us, that was in the form of dust, circumstellar dust orbiting stars like the sun. And Spitzer, one of NASA's great observatories, is supreme at detecting the heat radiation of orbiting dust particles. And those observations we made tracing that dust lead us to conclude that the processes that we think led to the formation of the terrestrial planets in our own solar system might be relatively common around other sun-like stars. And I think our audience knows that we have yet to actually see or image an exoplanet, an extrasolar planet, but we can see these protoplanetary disks?

The disks are relatively easy to see compared to seeing the planets themselves, and that's because the area that they occupy in the circumstellar environments around other stars like the sun is vast compared to the area occupied by a planet in orbit around the same kind of star. You talked about dust, and that's really key to this, and what you've learned, not just from the dust that's there, but when the dust isn't there anymore. Well, in our own solar system, we see dust that's generated by the collisions of rocky objects like the asteroids and the asteroid belt. And so it's not a great leap to say that the dust we see orbiting other stars like the sun might indeed be from the collisions of kilometer or larger sized objects generating dust. And in that same process of generating dust, also coming together to form planets.

And that is, again, the favorite model for the formation of the rocky planets in our own solar system. How did you arrive at this range of 20 to 60 percent, perhaps, of stars in our galaxy that may have rocky planets? Well, it's really a glass half-full or glass half-empty kind of approach, depending on whether you're an optimist or a pessimist. The observations that we obtained with the Spitzer Space Telescope, we made around stars of a range of ages. And we surveyed about 50 stars that have ages between 3 and 10 million years old and 10 and 30 million years old, another 50 stars, and then another 50 stars from 30 to 100 million years old, and so on. The whole sample is about 300 stars

arranged in these age bins of factors of three. And in each one of those bins, we saw that about 10 to 20 percent of the stars that we sampled showed evidence for this behavior, which we think leads to the formation of terrestrial planets. Now, what we can't say is how long the phenomenon that we see lasts. All we observe is this fraction of stars that show this behavior, and that fraction is really the product of how common occurrence this is and the duration of that phenomenon. So if this phenomenon lasts really, really short, then we're sort of undercounting. And if the phenomenon lasts really, really long, then we're overcounting in a sense, as we look at stars over this full age range between 3 million and 300 million years old. And so the pessimistic answer is that 20% of stars like the

Shun show evidence for behavior that we think leads to terrestrial planets. The optimistic result would mean that in each of our age bins, we're only seeing a short-lived phenomenon. It comes fast. The stars and dusty planetesimal belts around them sort of live hard and die young. And then the next generation would come in the next bin of stars, and so on and so on. And in that case, we would sum these fractions that we see and arrive at the optimistic result that more than 60% of sun-like stars show evidence for the formation of terrestrial planets. But even 20%, the worst case in this range,

is a good deal more than some astronomers suspected, I've read. Well, it varies. Your mileage may vary around that statement. I think there is a large camp in the exoplanet and planet formation community that would say, you know what, planets like the Earth are probably common around every star. would say, you know what? Planets like the Earth are probably common around every star. And you might call them optimists, but it's pinned on an underlying physical understanding of the process. If we go to our theoretical astrophysical colleagues and give them a circumstance such as the following. Suppose you take a swarm of kilometer-sized planetesimals and spread them out in an inner solar system around a star

like the sun and hit the go button, their theoretical models suggest that almost without exception, they will run away and lead to the formation of terrestrial planets. In other words, under the right circumstances, it's almost inevitable that you would form terrestrial planets. And so for many people, this wouldn't necessarily be a surprise. However, I should still caution that these results are really an interpretation, an assertion, if you will. And many of us are very excited about the ability of NASA's Kepler mission, which will launch next year, to test this assertion by really measuring that frequency of terrestrial planets through the transit light curves and the little dips in the starlight that will occur as Earth-like planets swirl around stars like the sun. There is a nice artist's rendering of Kepler doing its work,

the work that we hope it will do after its launch next year, on the article that a lot of my knowledge about this is based on by my colleague Amir Alexander. That's at planetary.org, and we'll put up a link to that, of course, where we keep the radio show at that website. But I don't think Kepler is all that well known as a mission that is scheduled for the near future. And yet it's going to have some great capabilities. I guess we only now, the lower limit on size of a planet is still about five times the size of ours? Well, that's right. The very smallest planets that have been discovered by a range of techniques,

including the gravitational microlensing, as well as the fine analysis of the radial velocity community to detect these tiny motions due to the wobble of a star as it orbits the common center of mass of a planetary system. Yes, that's right. Those mass limits are at the level of five to ten Earth masses. What do astronomers hope Kepler will be able to bring that limit down to? I can't quote the absolute limit. I'm not an expert on the Kepler mission, but I think it is the grand hope of the mission

to be able to tell us in any one-star system, there's always going to be wiggle room for how to interpret a specific light curve for a specific object. But in a statistical sense, after averaging over the many, many stars that Kepler will be able to observe, one hopes to arrive at this frequency of Earth-like planets around stars like the Sun. And if they're successful in doing that, that answer, whether it's 10 percent, 50 percent, or 90 percent, will frame the approach that I think NASA and our astronomical colleagues will take to answering the question when and where we can get the first image of an Earth-like planet around a star like the Sun. That's astronomer Michael Meyer. He'll tell us more about the new evidence of lots of rocky planets around the galaxy

when Planetary Radio continues. Hey, hey, Bill Nye the Science Guy here. I hope you're enjoying Planetary Radio. We put a lot of work into this show and all our other great Planetary Society projects. I've been a member since the disco era. Now I'm the Society's Vice President. And you may well ask, why do we go to all this trouble? Simple.

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or by calling 1-800-9-WORLDS. Planetary Radio listeners who aren't yet members can join and receive a Planetary Radio t-shirt. Members receive the internationally acclaimed Planetary Report magazine. That's planetary.org slash radio. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. Michael Meyer is a professor of astronomy at the University of Arizona's Steward Observatory. He led a team of scientists who have published findings indicating that at least 20 to 60 percent of stars in the Milky Way galaxy have rocky planets. They got most of their data from the Spitzer Space Telescope, peering at the disks of dust and gas surrounding stars that are younger than our own sun.

There he says that these disks coalesce into the menagerie of large objects that obediently circle stars, objects like our own Earth. Back to your results, is it fair to say that they essentially back up the existing models? I think that's what you were implying. I would characterize it that way. Our main goal of our project, we had a key project for the Spitzer Space Telescope called the Formation and Evolution of Planetary Systems. Our real goal of that project was to place our own solar system in context. How common are planetary systems like our own, around stars like the sun, amongst the myriad of sun-like stars in the Milky Way galaxy? Ironically, I think,

that's a poorly worded question. It really depends on which element of our own solar system one is focused on. Do you mean how common are gas giant planets like Jupiter and Saturn around stars like the sun? Or do you mean how common are asteroid belts or Kuiper belts around stars like the sun? Or do you indeed mean how common are terrestrial planets like the Earth and Venus and Mars around stars like the sun. Each element of that solar system architecture could be unique or could be common, and it's really the product of all of them together that give us the hope of identifying true twins of our own solar system. Now, our solar system is, I suppose, could be described as mature. It sounded like you were talking, you've been looking at stars

that range from infants to, what, adolescents? That's right, and we do, our sample does extend out into mature sun-like stars. Our oldest bin, if you will, was stars with ages of 1 billion to 3 billion years, not quite out to the 4.5 billion years of our own solar system, but relatively mature. What was also striking about our result is the time frame when we saw this activity, this bumping and grinding of these planetesimals that we think lead to terrestrial planets, persisted exactly over the range of times when we think the terrestrial planets were forming in our own solar system. There are models in the literature that suggest our Earth was 90% complete at ages of about 30 million to 50 million to 80 million years.

And that's very consistent with the observations we've seen. Also, our data suggest a rapid tail-off after the first few hundred million years of the evolution of these sun-like stars. And that, again, is consistent with what we think was the evolution of the warm dust in our own solar system. I should point out that this result is based upon observations of this heat radiation, tracing temperatures between about 100 and 300 kelvins, which we then, assuming things about the dust properties, map into orbital radii in the solar systems that we surveyed between one and five astronomical units. So roughly tracing dust between kilometer-sized planetesimals that would bump together and grind and generate dust between the orbits of Earth and Jupiter in our own solar system.

Fascinating. Where do we go from here as our search for and increasing knowledge of exoplanets moves into the future. And how about your own work? How do you hope to follow up this article in the Astrophysical Journal? Well, we have a range of studies leading out of our five-year program with Spitzer. Some of them are follow-up with Spitzer themselves to sort of target these interesting young stars in this very active time between 10 million and 100 million years old. And so we have a range of ongoing programs with Spitzer to slice and dice more finely the data around stars in that age range. I think the Kepler results that will start coming in the next few years will really test, as I said, this assertion that terrestrial planets are common. And if indeed they are common, I think it opens up a whole new way of thinking about how we can take pictures and get

pictures of Earth's around sun-like stars. The next generation of extremely large telescopes that are currently under planning and construction have the hope of, with the fineness of detail that they will have for the first time, to maybe, just maybe, if terrestrial planets are extremely common in that every star you see in the sky at night might have one, then you can look around the nearest couple of dozens. And if we're lucky, we might actually have a hope of taking a picture of one of those Earth-like planets around a Sun-like star. It will be extremely challenging, and it will be hard even for this next generation of behemoths

that will come on the scene in the next 10 to 15 years. But there's a chance it might work. And as this work gets refined, it will frame the next decades of NASA's plan to launch a series of satellites that will help in this regard and ultimately to lead to a terrestrial planet finder mission, which will be able to not only take pictures, but to get spectra of the atmospheres of Earth-like planets, and maybe even have a hope of looking

for non-equilibrium chemistry in the atmospheres of those planets, which might be a telltale sign of biological activity. Something to very much look forward to. You know, when I was talking to Mark Swain of JPL, I said that one of the reasons I love to talk to you guys who are working in this area is that you are gradually filling in that wonderful equation that Frank Drake came up with so many years ago, at the far end of which you have not just life, in his case, but intelligent life. Is that something that you ponder now and then? We do, and I absolutely agree with you. I mean, we live in interesting times, and the ability to fill in terms,

factors in that equation for the first time, not just the frequency of planets over all masses, but even the fraction of those planetary systems that would have Earth-like planets, and then maybe even to address whether planetary systems might have life. That's a remarkable spine-tingling possibility. Well put. Michael, thanks so much for spending a few minutes with us on Planetary Radio. It's my pleasure, Matt. Michael Meyer is generally a professor of astronomy at the University of Arizona and its Stewart Observatory, but this year he is spending time at the Harvard-Smithsonian Center for Astrophysics, and that is where we have spoken to him today.

And he continues his research into exoplanets, extrasolar planets, finding those other worlds that are perhaps throughout our galaxy. I'll be right back with Bruce Betts for this week's edition of What's Up, but first we're going to hear from Emily with Q&A. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, why are Martian sunsets blue? It's true.

Sunsets on Mars are the reverse of sunsets on Earth. Here, our blue sky becomes reddish near the horizon as the sun sets. Mars has a red sky that becomes blue near the setting sun. Why does this happen? Earth's blue sky is caused by light bouncing off of oxygen and nitrogen molecules in the air. When the sun lies near the horizon, its light must take a much longer path through the atmosphere to our eyes, and along the way it encounters lots of atmospheric particles. Smoke, soot, and volcanic dust cause not just blue light,

but also many other wavelengths of light, including green and yellow, to bounce away. Only the longest wavelength red light gets through to our eyes. Mars has a much less dense atmosphere than Earth, so the sky might look quite dark if it weren't for the huge amount of very finely particulate red dust floating in the thin air. That red dust is what gives the Martian sky its pinkish appearance. Paradoxically, the red dust is also responsible for Mars' blue sunsets. The blue sunsets don't have anything to do with the color of the dust. They have to do with the size of the dust particles. Very tiny particles tend to forward scatter light.

You notice forward scattering when you look almost directly at a light source, and tiny particles between you and the light source diffract the light toward your eyes. The particles forward scatter short wavelength blue light more efficiently than long wavelength red light, so Martian sunsets appear as blue halos in red skies. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. We just passed Merle Haggard Drive.

Well, that must mean that this is a mobile version of What's Up. Bruce Betts, Director of Projects for the Planetary Society. Where are you, Carmen Sandiego? I'm in the agricultural heartland of America, the Central Valley of California. And Merle Haggard Drive. Yes, yes, approaching Oildale. Coming south, returning from Sacramento where you had a visit with family,

and ready to talk about the night sky. I am indeed. It's a lovely night sky, but I shouldn't look at it right now. No, please don't. It's bad enough you're on the phone. Pre-dawn, pre-dawn sky, you check out Jupiter looking extremely bright, star-like object over in the east before dawn, getting higher and higher over time. star-like object over in the east before dawn, getting higher and higher over time. We've got in the evening sky, Mars, high in the west, orangish, looking like a kind of bright star. And farther to the east, also high up, Saturn looking yellowish, and in Leo, near Leo's brightest star, Regulus.

So that's the planet roundup at the moment. We go on to this week in space history. In 1970, in this week, China became the fifth nation to launch its own satellite. And then 20 years later, 1990, the Hubble Space Telescope was deployed. Still cranking and doing great and going to get a visit from shuttle in a few months. Wow. And if you're driving on this road, you can also search three-dimensional burgers sticking out of billboards. You must be getting closer to Southern California.

Yeah, I guess so. Do you play I Spy With My Little Eye except an astronomy version? Yes, that's exactly what we play. What else have you got for us? Got a big one? Yes, we's exactly what we play. What else have you got for us? Got a big one? Yes, we've got random space facts. Just the right amount of distortion. Mars.

Did you know the tops of the tallest Martian volcanoes, the Tharsis Bulge, with places like Olympus Mons and Arcea Mons. They are covered in fluff. Fluff? Fluff, basically dust fallout. And so when you look with thermal data, you see these things heat up and cool down very quickly because of the very small particle size up on top. So even though lots and lots, miles of solid basalt underneath, they're covered with dusty smut up at the top. Now, how do we know that this is dust? I mean, what if it's dry or lint? Well, we'd have to turn to the spectroscopy they've got now, and I don't know if anyone's actually looked for dry or lint, but that's a good question. I wonder what the spectrographic record of cotton is.

Well, I'm sure that's well done, but it's important to get it in its natural form of dryer lint. And I don't know. Maybe this will open up. Maybe I'll go back into the lab and check this out. Would you please? Okay, we can move on. All right, wait until I get past this Harley. On to trivia questions. We asked you last time around, what spacecraft crashed into the

moon on April 10th, 1993? Intentionally, I might add. How'd we do? You know, the best part of this, several of our listeners mentioned that when they Googled it, because yes, of course, we know that you're out there Googling these. But when they Googled this, guess what website had a page that came out on top with the right answer? Give up? Disney? No, us. It was us. It was the Planetary Society. The winning answer was at the top of the Google list, and it was

Hayten, a Japanese lunar probe. Indeed. Well, that's always gratifying when we're popping up to the top of the list. Hayten Higurumoro. Apparently, Higurumoro was a little add-on, a little hanger-on, a little pilot fish that was hanging on Hayten. Originally called Muses A, one of the worst names ever for a space probe, so it's good they changed it. Well, yeah, they like to name things that way. Once they get it up in space and working, then they change the name. Not uncommon with the Japanese space program. Well, our winner, by the way, and you have to trust me on this, it's not a fix.

You ready? David Kaplan. David Kaplan of West Simsbury, Connecticut. Absolutely no relation. Yeah, right. Cousin David. I mean, David has never won before. He indeed did get it right, and he was one of those who pointed out that when you Googled April 10, 1993, moon popped our website. Isn't that something? That is excellent. David, we're going to send you a Planetary Radio t-shirt. Okay, what else you got for us?

What's next week's question? Question for this week, if you want to try to win a Planetary Radio t-shirt, answer the following question. At the beginning of the so-called beginning of the space age, so let's say to be specific, when Sputnik launched, what was the largest ground-based telescope in operation? Largest ground-based telescope in operation, October 4th, 1957. Go to planetary.org slash radio, find out how to get us your entry, and compete to be the correct answer. Randomly selected to win that glorious Planetary Radio t-shirt. You've got until Monday at 2 p.m. Monday, the 28th of April at 2 p.m. Pacific time to get us that answer.

Can I get another few seconds out of you? The Planetary Society big event coming up in May and something kind of minor happening on Mars. Yeah, there's that Phoenix lander is going to be successfully landed for the first time in the polar regions of Mars on May 25th.

And we will have a planet fest in Pasadena at Pasadena Hilton. You can find out more information on our website if you're interested in attending. We will have live coverage of the landing on a big screen, and lots of people who know what they're talking about, and also me up there on stage.

And you can join the festivities. In any case, watch for that Phoenix landing. It should be exciting. I'll be there, too. I'm sure we're going to turn it into a radio show. But I hope that you can join us in person. It's going to be loads of fun. And I guess we're done. Where are you now? I'm in some thriving metropolis now.

Oh, I'm in Bakersfield. I really am in a thriving metropolis. Oh, you know, the old line, I spent a month in Bakersfield one night. We never get mail from anybody there, so I think it's okay to say that. Well, we're done. Let's do this in person next time. Alright. Goodnight, Bruce. Goodnight. Alright, everybody go out there, look up at the night sky, and think about creative smells that you smell while driving through Central California. Thank you, and goodnight. Been there, done that. He's Bruce Betts, the Director of Projects for the Planetary Society,

and he joins us every week here for What's Up. Join us next time for another jaunt around the universe. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week. Music Music Music Music