May 13, 2009

subscribe to JPL Podcast


Open with music
Interviewer: Is there another Earth out there?
I'm Jane Platt with NASA's Jet Propulsion Laboratory in Pasadena, California.
The Kepler mission, launched March 6 from Cape Canaveral, Florida, is in orbit now, getting ready to stare into space and look for planets like our Earth that might be orbiting others stars. Kepler Project Manager Jim Fanson of JPL joins us.

Fanson: Hi, Jane, its nice to be with you.

Interviewer: Even without Kepler, astronomers had found more than 300 planets orbiting other stars, but none of them are like Earth.  So Kepler's looking for planets like Earth. What exactly do we mean by that?  What is Earth like?

Fanson: What we mean by an Earthlike planet is to find a planet that's about the size of the Earth and that orbits its star at Earthlike distances, it orbits a star like our sun at Earthlike distances. And that means that it orbits at a distance from the star where the temperature of the planet is not too hot and not too cold, but is just right for the presence of liquid water  on the surface, where you can have oceans, you can have liquid water in which to have biochemistry, which we believe underlies all forms of life that we understand. So we're looking for a planet that could be habitable, the way the Earth is.

Interviewer: Which leads to the next question, which is what is the ultimate goal of Kepler?

Fanson: With Kepler we're trying to answer the question, "How frequently do planets like earth, that is planets the size of the Earth and orbiting in the habitable zone, how frequently do planets like that form around stars in our galaxy?" As you said, we know of about 350 planets now orbiting other stars, but finding planets the size of the Earth in the habitable zone is just an extremely difficult measurement to make. And that's what's driving us into space, trying to make this measurement above the Earth's atmosphere, where you can get much higher precision.

Interviewer: Tell us a little bit about the technique that Kepler's using to look for Earthlike planets.

Fanson: Kepler is going to use a somewhat different technique from the method that's been used to find the bulk of the planets so far. We're going to use a technique called transits. And a transit is an easy thing to understand. It's simply a planet orbiting a star, passing in front of the star as seen from our point of view. So that for a few hours as the planet orbits, it blocks some of the light from the star from reaching us. And we can measure that change in brightness, or that slight dimming, for the period of hours it takes the planet to go across the star. And so the planet will reveal itself by blocking part of the star's light, and it does that once per orbit, and so by that method, not only can we determine the size of the planet, by the depth of the dimming, but we can also determine the orbital period, or how far the planet is from the star. So there's a wealth of information that we can get from this technique.

Interviewer: So obviously this involves some pretty sophisticated technology, tell me a little bit about the telescope, how powerful it is and what it can do. Without getting into the nitty-gritty of it, just a little bit about how it works.

Fanson: To do a measurement of how frequently Earthlike planets form,
We need to look at a very large number of stars for a very long period of time.
Most of the telescopes we build on the ground or we put in space, what we're trying to do is magnify things that are very far away and very faint, so we can get a very high-resolution look at what's going on in the distant universe. We have the opposite challenge with Kepler. We need a very large field of view so we can simultaneously look at a very large number of stars. So we've built a special kind of telescope called a Schmidt telescope, and the field of view is equal on the sky to two dips from the Big Dipper. So it's 100 square degrees of sky, or another way to look at it, our field of view is about 30,000 times larger than the field of view of the Hubble Space Telescope. So it's a very different kind of telescope, and it allows us to stare at a region of the Milky Way galaxy rich in stars and monitor 100,000 stars simultaneously for a period of years.

Interviewer: Talk briefly about the camera on Kepler--it's a big camera.

Fanson: As I mentioned, we need to look at a large number of stars. So not only does the telescope bring in this large field of view on the sky, but to image that and to collect the data, we need a very large camera. If you think of the detector that's in your pocket camera, your one-shot digital camera, it'll have a CCD, or a charged couple device, in it that's about the size or your fingernail. The size of the focal plane on the Kepler camera is one square foot. So its physically extremely large, it's the largest camera focal plane we've ever flown in space. And if you think of a camera you would buy for your private use, if you have a really good camera, you might have a few megapixels. Well, the Kepler camera is 95 megapixels. So it's just a very large camera by any measure.

Interviewer: You've been working on Kepler for a long time, as have many people on the team. It's really a nerve-wracking process getting a spacecraft launched, and then getting it to work properly and getting confirmation it's working. You recently got an image with millions of stars. That must have been a really great day for you.

Fanson: It was a great day. You have a couple of critical events in the life of a mission like this. One of them is you light the fuse on the rocket and you take this ride into space, and you hope everything goes well. In the case of Kepler, everything went extremely well. And then in the life of a telescope, another critical event is you take your first image and you determine are you in focus, is everything working, ya' know, did you break any glass on the telescope?! And we're very gratified with our first light image to see these millions of stars glittering across the focal plane, everything was in excellent focus, everything was working as designed, it was a tremendous relief and very gratifying.

Interviewer: Kepler is a 3-1/2 year mission. At the end of 3-1/2 years, what is your hope and what is the plan for what information and what knowledge we'll have that we didn't have before Kepler?

Fanson: At the end of 3-1/2 yrs, we should know whether planets like the Earth are common or rare in the galaxy. We don't know whether Earths will be plentiful or whether the Earth is unique. And this is a question that has come down to us across a hundred generations of human history, and we stand on a technology finally that allows us to answer this question scientifically. So at the end of 3-1/2 years, we're going to know whether there can be Star Trek in our future or whether there's no place to go.

Interviewer: More information on the Kepler mission is online at  .
Thanks for joining us for this podcast from NASA's Jet Propulsion Laboratory.
Music fades.