Date: February 12, 2012
Title: Encore : The Search for Other Habitable Worlds
Podcasters: Geoff Marcy
Organization: Center for Science Education at UC Berkeley’s Space Sciences Laboratory
This podcast originally aired on May 28th, 2009:
Description: With over 200 “exo-planets” already discovered orbiting nearby stars beyond our solar system, planet-hunting astronomers have now turned their attention toward the search for Earth-like planets. Astronomers pursuing these “other habitable worlds” will soon have a new tool at their disposal – the ground-based Automated Planet Finder (APF). The 2.4 meter robotic APF telescope being constructed at Lick Observatory includes a highly sensitive spectrometer that will help launch an exciting new phase of exo-planetary science. In this Podcast, Astronomer Geoff Marcy will explain the need for the APF, and the fascinating science behind the latest exo-planetary research.
Bio: Geoff Marcy is an astronomer at the University of California Berkeley and leads the California-Carnegie Planet Search Team which is overseeing the construction of the APF. He is an elected member of the National Academy of Sciences and has been the recipient of numerous awards, including the 2005 Shaw Prize, Discover Magazine’s 2003 Space Scientist of the Year, the NASA medal for Exceptional Scientific Achievement, the Carl Sagan Award from the American Astronautical Society, the Beatrice Tinsley Prize from the Astronomical Society of the Pacific, and the Henry Draper Medal from the National Academy of Science.
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Ruth: I’m Ruth Paglierani from the Center for Science Education located at UC Berkeley, and I’m here at the UC Berkeley Astronomy department with Dr. Geoff Marcy, talking with him about his pretty exciting search for exoplanets and the Automated Planet Finder that he and his amazing team are working on at Lick Observatory. Geoff, if you don’t mind, I’d like to ask you a few questions about your search for exoplanets, and let me start by asking you, what exactly is an exoplanet and how are they different from planets in our solar system?
Geoff: Well, the term exoplanet simply refers to planets that orbit other stars. In the night sky, those twinkling lights you see are actually suns in their own rights, some larger, some smaller than our Sun, and those stars are in fact orbited, we now know, by planets, just as our own sun is orbited by eight major planets. So, one of the great questions that humans have had for, frankly, thousands of years is whether or not the stars you see at night have planets, what’s the diversity of the properties, the characteristics of those planets, and most interestingly, are there earth-like planets around them?
Ruth (1:16): So, everything that you have told me is quite compelling, but what I’d like to know is what drives you, personally, to want to search for those exoplanets?
Geoff: I’m really curious as to whether there are other earths out there and how different those Earth-like planets are from our own Earth. We wonder, and we wonder for good reason, whether or not there are rocky planets like Mars, Venus, Mercury and the Earth, but you can see already that among those four planets orbiting the sun, that they are extremely different from each other, and that begs the question, are there other Earth-like planets out there even more different from our own Earth than our friends here in the solar system? The question, of course, is most dramatic, as to whether or not those other earths can sustain life—as we know it at least. Are other Earth-like planets habitable and what are the properties of another earth that render it habitable? Is it the temperature, the atmosphere, the chemical composition, the presence of oceans, lakes, etc. Does the moon make a difference? Does having a planet Jupiter nearby matter? And, so, we’re just now beginning even to ask the right questions about what types of earths, if any, are out there and what they are like.
Ruth (2:39): So, how do you find these exoplanets?
Geoff: Well, we have two primary ways of finding planets around other stars. The way my team has been successful—Debra Fisher and I have been working on this for many years—is to watch the star rather than the planet. And the reason is that stars are much brighter than planets and they actually wobble due to a planet orbiting the star, pulling gravitationally on the star. So, if you watch a star in the night sky, if it’s orbited by planets, you’ll see the star wiggle around, do a little Irish jig in space, as it’s tugged to and fro by its planets. That technique has been very popular, we actually use the Doppler effect to carry it out.
Another technique is coming online now, very exciting and very powerful, and that is, to watch stars’ brightnesses. If a star dims, that would happen because a planet crosses in front of the star, blocking some of the starlight. And as the starlight is blocked, the star dims. You notice it in your telescope. And you can infer the presence of a planet and the size of the planet, because of course a bigger planet blocks more of the starlight. So we’re actually able to detect big ones but also the smallest planets and with a space-borne telescope called Kepler coming online, we hope to find Earth-like planets for the first time in human history.
Ruth (4:10): Now, I’m assuming, but tell me, could I see that wobble from here on Earth without a telescope?
Geoff: Sadly, your human eye just isn’t quite sensitive enough to see the tiny wobble of the star, nor is your eyeball sensitive enough to see the dimming of a star as a planet crosses in front. And therein, of course, lies the challenge. We need huge telescopes on the ground, here on the Earth, and also large telescopes in space above the Earth’s atmosphere.
Ruth (4:40): Great, well thanks for that. So, you work with a team of people, I’m sure you don’t work all by yourself, so my question would really be is, how do you and your science team decide where you’re going to search for these exoplanets? Now space is a big place, there is a lot of stuff out there, and there must be some that you feel maybe have characteristics that make them more likely to harbor exoplanets.
Geoff: Well that’s absolutely right. With our wobble technique, we very carefully choose the stars in the night sky that we want to observe for planets. And I’ll tell you one of the tricks that very few people know, it turns out that the youngest stars are kind of violent and active and they wobble on their surfaces due to magnetic fields, thereby confusing us. So we actually choose stars that are more adolescent in age and older. The older stars have become more quiet, quiescent. They don’t have flares and spots on their surfaces and they’re much more stable for detecting their own wobbles.
Ruth (5:50): So are you looking for middle aged stars?
Geoff: Middle aged stars are the best. Older stars are fine as well. And indeed our Sun is a middle age star. Our Sun, you may know, is 4.6 billion years old and the age of our whole galaxy with its 200 billion stars, is about 10 billion years. So our Sun has an age that’s about half that of our entire galaxy.
Ruth (6:19): So, I guess the other question that I want to know is, I know you’ve been very busy, you and your team, so exactly how many earth-like exoplanets have you been able to find?
Geoff: Well, this is a little embarrassing. I’ve been hunting for planets for 15 years, I haven’t found one earth. Not one! And it’s not for lack of trying, we’ve tried very hard. Debra Fisher and I, [and] past collaborators have worked very hard at it. The trouble is, an Earth-like planet is actually very small in the cosmic context. Earth’s are about 1/300,000th of a sun-like star and so earths are like little specks of dust against a fireball. And that’s why they are hard to find. We have some new tricks coming online that will help us, though.
Ruth (7:04) And what kind of tricks are those?
Geoff: Well, the most exciting thing going on right now is that this year, 2009, we launched the Kepler telescope. It’s a one-meter telescope, into space, above the Earth’s atmosphere, that was designed specifically to monitor 100,000 stars in the constellation Cygnus, specifically for Earth-like planets. And the way it works is very simple, we watch 100,000 stars to see which of them dim. If an Earth-like planet crosses in front of a star, it blocks some of the starlight, causing that star to dim. And not just once! Every time that Earth orbits around the star, there will be another dimming, so we can check our answer and be sure that we’re right. Kepler will offer us the chance—and when I say “us,” I mean all of us humans on the surface of the Earth—to detect Earth-like planets around other stars, for the first time in human history.
Ruth (8:07): Now what do you expect to find on these Earth-like planets? What are you thinking you might encounter?
Geoff: Well, the most important question first-off is the temperature of these earths —and we actually can figure it out. Because every time that earth goes around the star, we know how long it takes that earth to go around in its orbit, and the longer it takes, the farther that earth is from the star. And the farther the earth is from the star, the colder it will be, because earths get their energy primarily from their host star, just as our Earth gets most of its energy from the Sun. And so we’ll know how much warmth the Earth-like planet around another star receives from that star.
Temperature is crucial, because it’s temperature that determines whether the water on that planet earth (Earth-like planet) whether the water is frozen into ice and snow, boiled off into steam, or instead, as Goldilocks said, has a temperature just right for the water to be liquid. And of course as we all know, we humans and other life-forms depend crucially on liquid water, not just to drink, but indeed our bodies are made primarily of water. And so, one of the great quests in astronomy is to find not just Earth-like planets, but lukewarm ones that might have their water in a liquid form suitable for life on that planet.
Ruth (9:42): Tell me why you’re so interested in finding these other potential habitations or places where you think there might be life.
Geoff: You know, we astronomers have to admit something: we’re behind the science fiction writers, sadly. While science fiction has depicted the aliens flying around in spaceships like Star Trek and Star Wars, scientifically we still have no evidence of life elsewhere in the Universe, except right here on Earth. And moreover, we have no evidence of intelligent life, technological life elsewhere in the Universe. So there’s this enormously, somewhat embarrassing question, that the scientists here —on this planet, at least—have not answered, and that is whether or not there’s life out there, and intelligent life out there. And clearly, life has a very good chance of starting up, spawning, on planets that are something like our Earth. Yes, life could form maybe on Jupiter-like planets, or wacky moons, but we’re looking for planets because they are the most like Petri dishes within which life can get kick-started, and indeed it’s those planets that might have moons around them, and maybe there’s life on the moons orbiting the planets, so planets are the proper focal point to hunt for life in the Universe.
Ruth (11:10): Well, I must say, it’s a very, very compelling topic. I guess the other question I have for you is, is there someplace folks might be able to go to find out more about this search you’re conducting for exoplanets?
Geoff: Well, the most exciting search is with this new NASA telescope, Kepler, and all of the techniques used by Kepler to find the planets are on a webpage, and the address is www.kepler.nasa.gov
Ruth: (11:45): And are we already starting to get data back from that mission?
Geoff: So, Kepler, as of April 2009, is just opened its dust cover yesterday, and in the next week it will look at stars for the first time ever, and starting May 2009, the first trickle of data will start coming in, and it’s really the summer of 2009 when Kepler will look full-steam for Earth-like planets in the constellation Cygnus.
Ruth (12:15): It should be a very exciting summer for all of us! Now, I have another question for you. You also are working on a project that I believe is called the Automated Planet Finder. Tell me a little bit about what that is. I hope that doesn’t replace scientists entirely!
Geoff: (laughs) It’s very exciting! At Lick Observatory, which is run by the University of California, we are building —and it’s almost finished—a dedicated telescope, a 2.4 meter diameter mirror, the same size as the Hubble Space Telescope, and this telescope, the Automated Planet Finder, at Lick Observatory will be used every night, night after night, hunting for Earth-like planets. It’s a daunting, challenging task, and we’re going to be using this wobble method, watching stars night after night to see if they wiggle due to a planet yanking gravitationally on the host star. But this Automated Planet Finder will be the first telescope ever dedicated to hunting for and discovering planets around nearby stars.
Ruth (13:16): Well, I can’t wait to find out more about that and hear more about the data that you’re collecting with that. But you know, I have another question for you. It’s more of a personal question, and what I’d like to know is, at what point did you know you wanted to be a scientist? What got you going into the world of science?
Geoff: Well, I was lucky. When I was fourteen years old, one day my parents came home from work and they brought an old, used telescope. It was a small telescope, a small mirror, and they brought it home thinking that the whole family would use it. I took one look at that telescope, and brought it up into my bedroom, and it never got out into the rest of the house. I actually looked out my window of my bedroom with that telescope every night, sometimes even crawling out the window onto the roof of my house and every night, night after night, I watched the night sky seeing Saturn, with its beautiful rings, Jupiter with its four Gallilean moons, the crescent shape of Venus, the craters on the Moon, and I was just enraptured, literally captured by the beauty of the Universe, the enormity, and the profound questions associated with our Universe really captured my attention.
Ruth (14:29): Well, I’m glad to see that it captures your attention every day here at UC Berkeley as well. So thank you so much for your time, and I think this has been a very interesting set of questions, and your response to them even more compelling, so thank you so much!
Geoff: My pleasure!
End of podcast:
365 Days of Astronomy
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