Planetary Radio: Space Exploration, Astronomy and Science - 100 Extrasolar Planet Candidates...and Counting!

Episode Date: February 10, 2003

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This is Planetary Radio. I'm Matt Kaplan. We return to our regular format, but we will remember Columbia and her crew, explorers all. Our guest this week is also an explorer. Dr. Steve Howell heads the Search for Extrasolar Planets project at the Planetary Science Institute. That search is surely one of the great scientific success stories of our time. Later, we'll get back together with Bruce Betts for What's Up, including our new trivia contest. Later, we'll get back together with Bruce Betts for What's Up, including our new trivia contest.

First, though, here's Emily with the tale of two suns and some extrasolar action of her own. Hi, I'm Emily Lakdawalla with questions and answers. We were asked, is it possible for planets to form around binary stars? Science fiction movies set on other worlds often show skies with two stars, indicating that the world is orbiting a binary star system. These star systems are very common. A survey of stars close to the Sun reveals that half are actually binary star systems. In fact, the second closest star to Earth, Alpha Centauri, is actually a pair of Sun-like stars orbiting each other at an average distance

of 23 astronomical units, roughly the same as the distance between our Sun and the planet Uranus. But is it really possible for planets to form in such a binary star system? Stay tuned to Planetary Radio to find out. Dr. Steve Howell, how many planets do we Earthlings now know about? If you mean outside our solar system? You can include R9. R9 plus something of order 100 candidates. I would say that maybe 10 or 15 of those are absolutely for sure other objects that we might call planets. The rest of them are likely candidates, but not proven, so to speak, in the astronomical sense.

Now, if you went back 15 or 20 years, we would know about the nine that we live pretty close to, right? That's all we would know about, exactly. This is an incredible time to be alive, and I would imagine a pretty exciting time to be somebody who's very much a part of the search for extrasolar planets. It is indeed an exciting time. In fact, one of the aspects, of course, in the search that we all really hope we get to one of these days is to find planets that are much more like the Earth. The planets so far are more like the planet Jupiter, although their orbits are much different. But when we start

getting to smaller and smaller planets, and in particular, if one day we find Earth-like planets, that'll really add to the excitement. Now, the only reason that we haven't found Earth-like planets so far, right, it's not that we know they're not there, it's just that we're still getting better at finding smaller objects. That's correct. The way that planets have been found to date, all of them except possibly one, have been using spectroscopy. And this is commonly called the radial velocity method or the Doppler shift method, where

you basically look at a fairly bright star, and you notice that the spectral lines produced by that star periodically shift back and forth. And by doing an analysis on these data, you can say something about the orbital period of the object that's orbiting around the sun or around the parent star, if indeed there is an object, and you can infer its mass. And these measurements are very, very precise, but they're also difficult to make once the star gets fainter or the planet gets less massive. So all the planets found so far by that method are about Saturn's mass or larger.

So pretty good-sized planets, quite a bit larger than Earth. That's correct. Likely to be the same kind of planet that we find in, well, the gas giants in our solar system, Jupiter, Saturn, Uranus, and Neptune. Well, that, of course, is what we originally thought. Of course, almost all the planets we know about that may be like these gas giants are also in orbits that are the size of the Earth or smaller, very unlike our solar system. That's one of the surprises, right?

Absolutely. That's a very big surprise. Five years ago, we all knew how to make a solar system. You had rocky planets inside and you had gas giants outside, and we knew how to do that because we had a solar system as an example. Now every solar system we've found is different from our own. Which is one of the exciting things about science, isn't it? Oh, absolutely. It's caused all the people who make planets to go back to the drawing board.

And, you know, in great spirit of astronomy, in a year or so after the first planets were found, they, of course, came up with theories to predict why there should be gas giants orbiting very close to parent stars. Let's talk about how you are involved with this work. And it is through an agency that our listeners may already be aware of, and that is the Planetary Science Institute, but specifically a project that is sort of hosted by PSI,

the Search for Extrasolar Planets. And you are the project director. That's right. We have a project that the Planet society has has graciously provided some support for where our search is going to be slightly different from most of the searches that are out there the searches that exist now are as we talked about already mostly searches that are doing spectroscopy looking for radial velocity motions and there are indeed a large number of searches that are looking for photometric signatures of extrasolar planets.

And in that particular mode of operation, you actually watch and see if you can observe a very small dimming of a star's light, which is caused by a planet actually transiting across in front of that star. It's an incredibly small signal, but for planets the size of Jupiter crossing stars the size of our sun, it's actually quite measurable by modern techniques using very good imaging detectors. So the survey that we're doing at the Planetary Science Institute is a survey to look for planets much like those found already, but to not survey the brightest stars, which are generally very close to the sun, but to survey very distant stars,

to look in various parts of our galaxy and see if the frequency of Jupiter-sized planets, like those that have been discovered so far, are the same throughout the galaxy. We only know so far that planets, extrasolar planets, exist within about 40 or 50 parsecs of the sun. And our search will look out to almost 1,000 parsecs. This work that you're doing out of the project at PSI relies on using a particular telescope. It does indeed. We have a telescope that's going to be almost completely dedicated to this search. It's a 1.3-meter telescope that resides on Kitt Peak

as part of the Kitt Peak National Observatory. The telescope was built in the 1960s actually as a test telescope to see if you could control telescopes remotely. In the 1960s, the experiment failed miserably. They tried to control it over telephone lines, and the technology of the day just wasn't capable of it. Of course, now it's very common.

That's right. It's very common now, and in fact, our telescope has been completely refurbished, and part of that refurbishment is a state-of-the-art computer control system, which hopefully by this spring or summer will be completely operational and we'll be able to control it over the Internet. Our guest is Dr. Steve Howell, a professor at UC Riverside in California, but also the project director of the Search for Extrasolar Planets, which is a major part of the Planetary Society's agenda.

You also receive assistance from NASA, I believe. We do indeed. We had some original seed money funding from NASA. And in fact, the last few years, our money from NASA hasn't been as voluminous as we would like, of course. There's a lot of competition now. And our particular proposal that went to NASA, along with probably hundreds of other proposals, it was given high marks, but it didn't make the grade. So that's a bit of a down size for the project for maybe the next few months. But, of course, in the proposal game, that's the way it is. You always have wins and you always have loses, and when you lose on a proposal, you just regroup and try something else.

I take it the Planetary Society is hanging in there. They are indeed. They've been great supporters of us, and they will continue, I believe, to do that. It is really part of NASA's mission, at least as they have defined it so far, to assist generally in this search for extrasolar planets. That's right, and NASA is doing quite a bit in the terms of looking for extrasolar planets. They are funding a number of ground-based searches, primarily those doing radio velocity studies. Those are the searches where you can infer the masses of the planets you find very well.

Where our search being a photometric search, it's a little tricky to know the mass. You find the size of the planet, but knowing the mass is a little different, although you can assume it's sort of like Jupiter and use an average density, and knowing its size, that gives you a good handle on the mass. In fact, about as good as the radial velocity people can get. But NASA also is looking for planets in a much more costly way, and that is through the Kepler mission. The Kepler mission was chosen about a year ago as a discovery mission. It's going to be launched in 2007. And the Kepler mission, of which I'm also a participating scientist on,

will be probably the first mission on the ground or in space that could have the possibility of detecting Earth if they exist around other stars. Which is exactly the direction I was hoping to go in, but maybe we should take a break first, and then return and talk about how the search for extrasolar planets, how the technology used in that search, is improving to the point where we start to think realistically about finding planets not unlike our own Earth.

Our guest is Steve Howell. He, as I said, is a professor at UC Riverside, but also a major player in the search for extrasolar planets. And that's what we'll be back talking about again in just a minute. Please stay with us on Planetary Radio. This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary Society, the world's largest space interest group. The Planetary Society is helping to explore Mars.

We're tracking near-Earth asteroids and comets. We sponsor the search for life on other worlds, and we're building the first-ever solar sail. You can learn about these adventures and exciting new discoveries from space exploration in The Planetary Report. The Planetary Report is the Society's full-color magazine. It's just one of many member benefits. You can learn more by calling 1-877-PLANETS.

That's toll-free, 1-877-752-6387. And you can catch up on space exploration news and developments at our exciting and informative website planetarysociety.org The Planetary Society Exploring New Worlds Planetary Radio returns. I'm Matt Kaplan. My guest this week is Steve Howell,

Dr. Steve Howell of UC Riverside and the Project Director for the Search for Extrasolar Planets based at the Planetary Science Institute in Tucson, Arizona. And I imagine that means that you're out there in Tucson now and then. I am in Tucson about a third of my time, and as we talked about just before the break, if our telescope fully actually runs over the Internet,

then of course we don't have to be anywhere near the telescope to operate it. And those operations will, in fact, be probably advertised quite well on the Planetary Society webpage, and much of the data that we will get and much of the operations will be available to Planetary Society members. And we will, exactly as you've said, make sure that we keep up to date. There is a special section on the Planetary Society website, which, of course, is planetary.org. If you scroll down a little bit on the right side under our special projects area, you'll see it, Extra Solar Planets, and that will link you directly to the Search for Extra Solar Planets project at PSI, headed by our guest, Steve Howell.

Planets Project at PSI, headed by our guest, Steve Howell. Steve, before we went to the break, you mentioned a NASA mission, which I think you said is slated for launch, if all goes well, in 2007, the Kepler mission, which will be the, is it the first attempt to find smaller, more Earth-like planets? Yeah, Kepler was designed to do very precise photometry, much more precise than can be done from the ground, because if you're out in space, you don't have the Earth's atmosphere in the way. And both the atmosphere, which limits the precision you can do from ground-based telescopes,

but also the fact that if you're at any given observing site on the ground, you have times when you can't observe stars due to weather or due to the fact that half of the time the sun is up, where Kepler will be able to stare at a field of view for four years or longer, totally uninterrupted, and be able to search upwards of about 200,000 to 300,000 planets, I'm sorry, stars. Hopefully we'll find that many planets, too. I hope so. And be able to detect, of course, lots of the so-called hot Jupiters, tens of thousands of hot Jupiters. But the real cornerstone there, the real jewel, will be if it can find planets

that are the size of Earth. Beyond Kepler, I think there has been talk, at least speculation, about missions that might be sponsored by NASA for telescopes that would make the Hubble telescope look almost puny, which I guess might also help in this kind of search. That's true. The missions beyond Kepler are sort of a string of missions. One of them is really well into its development phase at this point. The other one's a little down the road yet. But these are the missions.

The first one is called SIM, S-I-M, which is the Space Interferometry Mission. And the one that we're all hoping we'll actually see fly is called the Terrestrial Planet Finder. And this is a very ambitious mission to put an interferometric array of telescopes in our solar system, but very much out near the planet Jupiter. And not because the planet Jupiter is there, but just move it far enough out of the inner solar system to get away from all sources of light that might disturb it. And there's a lot of dust left in the inner solar system,

which we see as the zodiacal light. So if you move farther out in the solar system, you get away from that dust and you have an even better view. And the terrestrial planet finder, the hopes there are that we actually would be able to look at, for example, candidates that were found by Kepler and look at those planets and actually get an image of the planets around its star. I don't even know if this is an appropriate question, but since interferometry actually allows you to have, in a sense, a virtual telescope with a tremendous mirror, can you even say, oh, this would be equivalent to an Earth-based telescope with a 300-inch mirror or whatever?

It's hard to say that because the actual scoping of the terrestrial planet finder isn't done, but also with interferometry, you do a couple of things. As you say, you use a bunch of mirrors in conjunction that give you an effective aperture that's larger. You also can allow the light

to interfere with itself, and thereby you can actually use a process called knolling interferometry, where you take the light coming from the parent star and you actually add it with light coming from itself but out of phase. You basically make the parent star disappear in your image, and then hopefully what you're left with is this little image of the planet that's orbiting around that star.

Fascinating. How many probes might the Terrestrial Planet Finder involve? How many space-based telescopes? I think right now it's slated at about six different ones that are connected by lasers, so they actually stay precisely the same distance apart. And there's something of one or two meter size right now. Wow. And as I've read about this, that spacing, to have an effective interferometer like this, is absolutely critical. Yeah, it's something of order. The spaceships have to stay within some distance of the order of atoms apart or something.

It's an incredible spacing. That might be slightly overstated, but it's very, very small. It's an incredible precision. And there is actually a feeling among engineers and scientists that we can achieve that kind of precision? Well, there is indeed, and this is, you know, 20 years in the future, and we're hoping we'll get there. This first mission I mentioned, the space interferometry mission, most of its purpose is to try a lot of these technologies,

as well as do science, but try these technologies in Earth orbit. And if we can do it in Earth orbit, then it's not simple, but then we just take that technology and move it out by the planet Jupiter or something. And not right by Jupiter, we don't want Jupiter in our way, but out at that distance from the sun. And if we can do it in Earth orbit, in principle, we can do it out there. distance from the sun. And if we can do it in Earth orbit, in principle, we can do it out there. When you talk about being able to actually resolve an image of one of these potential Earth-like planets, which no one has yet seen, but we all hope are out there,

are you talking about a resolution that might let us, let's say, see oceans or actual structures on the planet? Boy, that would be nice, wouldn't it? I think at this point, if we could see a little dot of light and say, look, we got rid of the star and there's a little dot of light, and then take a few images and show that that dot of light is actually moving as it orbits the planet, I think that would probably be the level at which we're talking about. Or the possibility of painting a spectrum of that object, that little dot. Even though it's a dot to our eyes, we might be able to get a spectrum that shows us all things like chlorophyll or water vapor or something that we feel really warm and fuzzy about and earth-like. Okay, well, one step at a time, and those are pretty big steps right there. So I guess we'll wait for that poster image.

Maybe when we're in retirement, we'll get to those kinds of visions. Maybe when we're in retirement we'll get to those kinds of visions. And who knows? Things might move faster. Let's go back to something you said at the beginning of our conversation. I think you said, and if we leave off the nine more familiar companions we have in our own solar system, well, eight companions and us, you said maybe 100 or so candidates, you called them, and 10 to 15 confirmed. What's it going to take to confirm some of those other candidates?

Well, let me step back just and define what I mean by confirmed. Confirmed are objects where I think the spectroscopic evidence is very, very strong. And in one case, the case of HD 209458, we also have that particular planet also a transit to the star. So in that particular case, we absolutely know it's mass. Those are candidates where I would feel comfortable saying that the masses are either known or the limits are known well enough that they're things that are like Jupiter or Saturn. They're that size and that mass, and we all would feel comfortable calling those planets. The rest of the objects are in a realm where work is being done

to put them more into this confirmed arena, where we also know that those are maybe one times the mass of Jupiter or two times the mass of Jupiter. But the vast majority of them to date, just because of the uncertainties either in the data or the uncertainties in the measurements or the faintness of the star or just observational parameters like that, they possibly could still be low-mass stars, such as brown dwarfs.

Now, they probably aren't, but where the line between that is drawn is kind of fuzzy these days. between that is drawn is kind of fuzzy these days. Low-mass stars, very, very small things like brown dwarfs, have masses of maybe 20 times the mass of Jupiter, up to maybe 40 or 50 times the mass of Jupiter. So if you have observational data that has some uncertainties in it, just due to the fact that we can't maybe measure very precisely or the angle of the orbit of the planet going around its parent star, you might have uncertainties where you don't know if

the mass of the object is four times the mass of Jupiter or 15 times the mass of Jupiter. So those are the kind of uncertainties that are slowly being worked on and slowly, planet by planet, they're being put in boxes. Oh, it's a good planet. Oh, this could be a low-mass star or a brown dwarf. But progress every year and maybe even month by month. That's right. Progress is going.

I mean, there are websites that you can find. I think the Planetary Society website lists a bunch. If you just go to any web browser and do a search on extrasolar planets, you'll find many, many sites. Jeff Marcy, for example, at UC Berkeley has a site, and they have updates almost daily on what's going on with all these various candidates, new ones that come along, information on the old ones. Lots of people, lots of astronomers are working hard to confirm as many as they can, of course.

We'll put up some more of those links, if we can, on the Planetary Radio area of the Planetary Society site. Steve, we've got less than a minute left. I've got one more big topic that's going to be hard to crowd into a minute, but I'm sure you and a lot of our listeners are familiar with the famous Drake equation. That's right. Frank Drake, one of the pioneers of SETI. We won't go into detail here.

You can find it elsewhere in the SETI section of the Planetary Society website. But, of course, that equation created by Frank Drake has a bunch of variables. And you, at the end of the equation, end up with how many advanced civilizations there might be in the universe. That's right. You must have some thoughts about the fact that you are filling in, in a sense, one of those variables early in the equation, and that is the number of planets and maybe soon Earth-like planets in our galaxy. Absolutely.

And I'll tell you, that's just phenomenal footsteps to be following in, and what a tremendous scientific endeavor to be part of, filling in parameters in what's got to be the most important pursuit of mankind, is are we alone or are we not alone? And either way, I think it's, you know, quite amazing and quite scary in some respects, whether we are or aren't alone in the universe. Steve Howell, it is fascinating work, and we will continue to follow it, and I'm sure we'll want to have you back here on Planetary Radio. Oh, thanks very much. It's been a lot of fun, and I encourage the listeners to check out the websites, and if they have questions or something, there's addresses on

there for myself and other people. Please get in touch. We'd love to talk to you. You bet. The Extra Solar Planets special section of the Planetary Society website, planetary.org. My guest has been Dr. Steve Howell. He's a research professor at UC Riverside here in California but also spends a lot of time

at the Planetary Science Institute in Tucson, Arizona where he is the director of the Search for Extra Solar Planets project. Planetary Radio will in Tucson, Arizona, where he is the director of the Search for Extrasolar Planets Project. Planetary Radio will continue in just a moment. Hi, I'm Emily Lakdawalla, back with Q&A. Can planets form in binary star systems? The answer is probably yes. Planets can exist in binary star systems in one of two places.

One possibility is for the planet to form far enough away from the two stars that they act gravitationally like a single big star. In this case, the planet would have a double sun, with the two stars always rising and setting at about the same time close to each other in the sky. It's also possible for a planet to form close enough to one of the two stars that the other star's gravitational influence on the planet is slight. In this case, the planet's sky would contain two different suns that rise and set at different times, just as our sun and moon rise at different

times. One sun would probably be dimmer than the other, and there would be different brightness days and nights depending on the different rising and setting cycles of each star. For our neighbors, Alpha Centauri A and B, mathematical modeling suggests that there is a gravitational safe zone around each star that could contain planets in Earth-like or Mars-like orbits, so it's very likely that there could contain planets in Earth-like or Mars-like orbits, so it's very likely that there are many planets in our galaxy with more than one sun. Got a question about the universe? Send it to us at planetaryradio at planetary.org, and you may hear it answered by a leading space scientist or expert. Be sure to provide your name

and how to pronounce it, and tell us where you're from. And now, here's Matt with more Planetary Radio. Time once again for What's Up with Dr. Bruce Betts, the Director of Projects at the Planetary Society. Welcome back, Bruce. Thank you very much. What's up this week? Well, we've got all five naked- planets are naked eye once again this week. So in the evening, you can see Saturn.

It's already up fairly high in the east by sunset. And by 9 or 10 p.m., it'll be directly overhead. And if you're familiar with Orion, look above Orion, and it will be the brightest thing in that area, but not a lot brighter than other things in that area. Jupiter is rising right at sunset and setting right around sunrise and midnight right overhead because it is at opposition, the opposite side of Earth from the sun. Well, it's a great time, as you've been saying for several weeks now,

to do some of this observing. What else do you have for us this week? Well, this week in space history, we go to the sports page. On February 6, 1971, as part of Apollo 14, Alan Shepard hit a golf ball on the moon. Famous story. Famous. And, of course, we have video of that as well. Yes, we do.

A reported 400 yards, but it's still debated. 400 yards? Yeah. See, I'm not a golfer. Isn't that... I mean, that's a nice drive, isn't it? That would be a tremendous drive. It would be, okay.

But it's a tough call. He's wearing a space suit, but he has a lot less gravity. There's rumors that Alan Shepard just made it sound better than it really was. Please. But golfers would never lie about such a thing. And who's going to prove him wrong? And what I'm waiting for, of course, is how soon

will the scavenger hunt be to recover that ball? We're trying to raise funds for the Planetary Society right now for that important mission, help us recover Alan Shepard's golf ball. Now, you know what? We didn't get a chance to put the echo in this time, so say something I can put echo behind. Okay. Trivia contest! Okay, that'll do.

Let's review last week's question, first of all, which was... Who was the first American to eat food in space? We had seven or eight, I've lost count actually, correct answers. And I don't know if people were just taking lucky guesses or if they looked it up, because it is what I would bet a lot of people would guess. It was John Glenn. It was indeed John Glenn, which in some ways to me is surprising because he wasn't up there that long, just a few hours.

But they wanted to make sure that someone actually could eat in space, although Yuri Gagarin had done it for the Soviets. I don't know how well publicized that was at the time. So basically they wanted to make sure he didn't choke on his food. It was Soviet food anyway for Gagarin. Well, yeah. Anyway, let's not go there. All right.

So you probably want to know who won our trivia contest. I do. Who won our trivia contest, Matt? It was Christine O'Brien. Christine O'Brien. One of many correct answers, John Glenn, that were submitted. She is in Torrington, Connecticut. John Glenn, that were submitted.

She is in Torrington, Connecticut. And out there in Torrington, Christine, you will soon be able to wear your lovely Planetary Society Carl Sagan Memorial Station T-shirt. Indeed. And also we have the thing of the first American to eat high-protein bars in space, later marketed, that you said you enjoyed. Oh, yeah, space bars. That's right. Which was Scott Carpenter eating the first Pillsbury-produced bars and also Nestle sent along some on the same flight. When I was a kid, yeah, as soon as I learned that these were genuine space food bars,

I must have eaten those every day for, you know, a couple of years. How'd they taste? Awful. Terrible. Terrible. But they were space food. The power of the space program. Once again, ladies and gentlemen, on to this week's trivia question.

What is the most distant object from Earth that was built by humans? Ah, okay. Now, there are several candidates for this. We won't even mention the name of some of those candidates. How far out has the reach of humankind made it? And we are beyond the solar system now, aren't we? Not really. Oh, not quite?

They're exploring the edges. There are different ways you can find the edges, and maybe we'll come back and discuss that a little more as well as tell people how far away things are in next week's show. Well, tell people, first of all, how they can enter the contest this week. Go to our website, planetary.org, and follow the links to Planetary Radio, and from there you'll get instructions on how to enter. That's it, Bruce. Thanks once again for joining us. Thank you, and buckle up and drive safely.

Bruce Betts is the Director of Projects for the Planetary Society. Thank you! Good night! Gotta love him. Matt Kaplan here, hoping you'll join us again, same time, same station, same website, for the next edition of Planetary Radio. Have a great week, everyone.