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The Science Behind NASA’s Kepler Mission
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Jesse Carpenter: NASA's Kepler Mission, a collaborative scientific study. Hi, I'm Jesse Carpenter and you're listening to a podcast about NASA's Kepler Mission from the NASA Ames Research Center. Planned for launch in March of 2009, the Kepler space telescope will observe one area of the universe continuously for a period of four years in its mission to identify the presence of planets that are similar to Earth. Today we have three Kepler project team members who are here to discuss the broad based scientific effort that will support the Kepler mission. Joining us in our studio are Kepler Principal Investigator William Borucki from NASA Ames, from the Harvard-Smithsonian Center for Astrophysics we have Kepler Co-Investigator David Latham and from the Space Telescope Science Institute we have Kepler Co-Investigator Ron Gilliland. Welcome to everyone, and thank you for joining us. Bill, tell us a little bit about the collaborative effort behind Kepler.

William Borucki: Today I want to talk a little bit about the group of scientists that have come together to make this mission possible. And the group is very, very diverse. We have people like Natalie Batalha from San Jose State University who have chosen this field of view, a field of view that's rich in stars. Of the 13 million stars in that field of view, which are good targets? Which are stars like the sun, rather than giants, which have expanded and consumed their planets. And so, that catalog was developed by some of our co-investigators, Dave Latham, who is with us today, Tim Brown and a number of other people who have worked together to build that catalog. Once we have the catalog and Natalie’s chosen the targets, that database gets observed by the telescope for several years, I think three and a half years right now is what we’re funded to do, we need to see the planet cross the stars several times before we're sure that what we’re seeing is not a spot on the star for example. So that data then comes down from the spacecraft to the deep space network, which is run by our colleagues at JPL. It moved from there to the Mission Operations Center, which is in Boulder Colorado, and there our colleagues look at this data and make sure that all of the pieces have been put together, because sometimes when the data comes down, there are holes in it, you've got to ask for the data to be sent down more than once. Then it goes to the Space Telescope Science Institute, where Ron Gilliland, on of our colleagues is there. The work they do there is to do calibration and actually, quite a bit of other work as well. The data moves from there to NASA Ames’ Center, where we analyze that data, and where the science team gets together. Many of the observers get together and look at this data and ask which are the best stars to look at. We see these candidates, but not all of them will be planets. Some will be grazing stars, some will be background stars, so the team's got to get together. And we have people who look at that from UC Berkeley, Geoff Marcy for example. We have Bill Cochran from the University of Texas. We have a person from Harvard, Dimitar Sasselov, who was actually in charge of building an instrument that will help us, especially to find the masses. To confirm that we’re actually looking at earths. We also have people who are looking at the instrument itself to make sure it's working properly and that its noise is low enough. And we have a number of people from the SETI Institute that are doing that work. Now we have a group of people that are participating scientists who have joined the team lately and they're doing special complementary things like they time the transits and say, "There are planets that you’re not seeing, but we can detect." So there's quite a range of people that have joined the team to work on this. This would be I think a good time for Dave Latham to talk about how we built that catalog.

David Latham: Well, I’m going to talk a little bit about the preparation of an input catalog that allowed Natalie to chose the hundred thousand or so best targets. That was a five year effort, involved a handful of people working at several different institutions, involved a lot of telescope time, more than three hundred nights of telescope time from an observatory in Arizona on Mount Hopkins, taking images on charged coupled devices and figuring out which stars are like the sun or maybe smaller. Even smaller stars are better because a planet blocks a larger fraction of the light around a smaller star. Because the reason we put in so much work for five years is so we can have fun after the thing launches. Because that’s when we’re going to get candidates for transiting planets and that's when we start doing follow up observations with ground based telescopes to figure out whether it's really a planet that we’re looking at or whether it’s a stellar imposter. Because it turns out that binary stars that eclipse each other can easily mimic a planetary system where the planet goes between us and the star. Stars are bigger than planets, mostly, so you might think it would be easy to tell them apart because the eclipse ought to be deeper for an eclipsing binary, but it turns out that there are configurations that can fool you. For example if the eclipse is grazing, if the two stars are just kissing each other, then it has a shallow depth to the eclipse event and you can confuse that. Or you can have three stars. It's amazing how common three stars are in triple systems, and you can have a bright star that is diluting the light from a fainter pair. So it turns out that these imposters are more common than the planets, so there's a lot of work that has to be done by a pretty large team of follow up observers from observatories around the country to sort out the losers from the winners. And in this context a winner is a transiting planet. So I imagine that altogether you'll have more than a hundred people going to telescopes, that now that I think of it, more than a dozen maybe two dozen observatories around the world, working on the follow up of the targets identified by Kepler.

William Borucki: That’s important because, Ron's group that he heads in the asteroseismology is tremendously important to us, because when we see a transit, the planet blocks the amount of light, the star gets dimmer in proportion to the size of the planet compared to the size of the star, but if you don't know the size of the star, you don’t know the size of the planet. And, the asteroseismology people have the best method of getting star sizes, so the asteroseismology program that Ron is coordinating is tremendously important.

Ron Gilliland: The surface of the sun and other stars has a large number of sound waves that are excited all the time by boiling action, of convection at the surface of the stars. And in particular, they tell us the size of the star as a whole. And that's very interesting to Bill and the general study of planets because our transit technique with Kepler, gives you very accurately what the size of the planet is relative to size of the star. But if you want to know what the size of the planet is, you need to know what the size of the star is.

David Latham: There’s another characteristic of stars that asteroseismology can help with and that’s the age of the star. You know, stars don’t have clock faces on them that tell us how old they are. It's really hard to figure out the age of a star.

Ron Gilliland: Stars make their light by nuclear reactions in the core of the star. And as the star ages, and the center of the star is transmuted into helium as time goes on. That changes the density structure of the star, and that changes the relative frequencies of the many sounds waves that we see at the surface of the star in a very characteristic way that allows us to estimate the ages good to maybe ten percent. So it's like being able to guess a fifty-year old person’s age to five years, which is pretty good. And to be able to do this, we’ve put together a very large and very international consortium of astronomers.

William Borucki: Not only do we want to talk to our colleagues, our scientific colleagues about what we’re finding, and getting their help on interpreting it, but we want to make sure the public is involved. And so Kepler has a very large education and public outreach program. Two of our co-I's are working on that aspect. We have someone from the SETI Institute, Edna DeVore a former teacher and we have a person involved from the Lawrence Hall of Science and these people are putting together lesson plans for teachers, they’re putting together planetarium programs, they’re putting together StarDate programs and all sorts of things to communicate to the public. And in fact, one of the things they’re doing, is they're saying as we find giant planets, not just the earths, but the giant planets, those giant planets can be seen from the Earth. And so we will be announcing to the public and to the amateurs, "Go out with your telescopes, you can actually monitor these giant planets transiting other stars." So there is quite an effort with our colleagues and our co-investigators to bring this to the attention of the public.

Ron Gilliland: Another way in which we broaden the scope in which Kepler will be available to the world at large is we have a general observer program where on an annual basis we allow astronomers from all over the world to write proposals requesting that specific stars that the science team with Kepler itself are not interested in that observers would be able to observe the stars for periods of three months or a year or perhaps even longer. And I'm sure that some of the stars that the general observers choose to observe will be very interesting variable stars from which we'll be able to learn things that are available in no other way.

William Borucki: And some of these stars of course, are very interesting in their own right. We have stars that are old; they have expanded so they actually touch one another. They transfer part of their star material to another star and that star might be a white dwarf and explode periodically. So there’s a lot of variable stars for the science community to go and look at. And in fact, when we have that advertisement for the science community to write these proposals, I’ve seen proposals where they say, "Not only do we want to look at some of the stars, but we want to look at some of the galaxies that are in your field of view as well." So there’s a lot material out there for people to learn about that are in our field of view. But we don’t change the field of view. It's a very large field of view, over a hundred square degrees, so it’s a big portion of the sky. And so there's a lot of targets of every type that we can study.

David Latham: One of the great things about working on the Kepler mission is there’s so much public interest in planets around other stars. I find it very easy at a cocktail party to tell people what I'm doing and I think that's, in my mind a measure of great science, something that involves the public's interest.

Jesse Carpenter: How important is the collaborative effort to the Kepler mission?

William Borucki: The collaborative effort of course is absolutely critical to what we’re doing. We have experts from all of these different fields and that’s what’s required to do this job well. No one person can do this. This really is teams from Europe, teams from the US, there are teams from other countries, other parts of the world as well. Each of whom knows how to do something really, really well. Ball Aerospace is a team member, not necessarily in the science they do, but in developing a spacecraft that will do this job for us. Their understanding, their knowledge, their engineering knowledge makes this possible. To manage such a large group of people, and the fact that we need the deep space network and we need so many other things, we have to have a very competent management team, and JPL has been hugely helpful there as well as the team here at Ames, so many different groups working together.

Ron Gilliland: Certainly on the science side where asteroseismology comes into play this is something that could not be done now without a large international collaboration. The expertise that’s needed is simply too broad for the resources that we have in any of the institutions that we have in the US. We really need a full international collaboration. The amount of data will be returned from the Kepler Mission is really astounding both in terms of simply the volume of data that’s returned, but also the number of stars that's observed and the range in behaviors we expect to see in those stars.

William Borucki: And I'd like to add to that, all this data comes down and the public and the science community is going to use it for decades. And it’s stored at the Space Telescope Science Institute where the public can get that data. They can look at the data in the raw form, they can look at the data after we’ve analyzed it, so it’s available to everybody for decades. And that’s a huge asset to the community.

Jesse Carpenter: I'd like to thank our guests Bill Borucki, David Latham and Ron Gilliland for joining us. I'm Jesse Carpenter and you've been listening to a podcast from the NASA Ames Research Center.

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