didates in or near the habitable zone, but we'll be also be spending a lot of our effort to confirm whether the candidates we know about today are planets.
Finding meaning in so much data, over such a vast amount of space and over a long period of time, must have its difficulties. How did you review the data?
One of the things that we spent a lot of time on was looking at the data and seeing if it was a false positive. For example, if you see two eclipses, then it's a small star. There shouldn't be a big eclipse and a small eclipse if it's a planet. There should be just the transit.
If the planet is hot enough, the life of the planet is cut off when it goes behind the star, so we look for that to see if the shape of the transit is right. The shape of a star passing over another star looks different from a planet crossing over a star. Another thing that bothers us quite a bit is that when you look into the galaxy as we do, there are a lot of little starsbillions of little starsand some of them are close to your targets. So a little star that's going through eclipses, an eclipsing binary, makes you think that it's your star, but instead, it's this background star.
When Kepler operates, it has a blurry image, so it doesn't saturate these stars and can't tell the difference. We have to go through a great deal of effort to make sure what we're finding isn't one of these background stars. We take the Kepler data and, using programs we built that search for what happens during a transit, we can tell if a background star is actually doing the transiting, because its brightness is changing.
We also go to the really big telescopes, and we get very sharp images to see if there's anything around that star that could explain it. When we're through with all those tests, we go to the Keck or the HET or another large telescope and we measure the spectra. If the spectra show that the star is wobbling, we get the mass of a planet. In particular, we can go to the Keck, get the period of the planet and get the epoch (where the planet is on its orbit). And that should exactly match what we have with Kepler. If they have the same orbital period and they occur at the same time, we can say yes, we have a confirmation and can announce it.
How did you develop the general concept of the Kepler Mission?
I did photometry for the Apollo program, and I realized 25 years ago that this would be another way to find planets. I realized that it would be a good method to find small planets. Radio of velocity doesn't do a good job finding small planets with long orbits, but photometry does fine. The trick was to develop a detector system that could have the precision that was required. So I started building photometers, for at least a decade, of different kinds and trying them out at observatories to see how they worked. I was finally convinced that we could build this into a spacecraft and go search for planets. At the same time, NASA came up with a new program called the Discovery Program, and I knew that would be big enough to carry the telescope we needed to put it into space. It took a pretty big rocket to put the Kepler into orbitit was the size of a VW van.
You've said that you have dreamed of discovering life on other planets since you were a kid. Was there one moment where you thought to yourself, wow, this is amazingthis is really going to mean something?
I'm a little hesitant to describe it, but I'll tell you. When I was a kid, I built rockets. And I had the privilege of going up to the big rocket booster, which was 15 stories high, and I thought, this is going to carry my experiment into space. It really made it real to see that giant rocket there, ready to make this work. It was really a special experience.
And of course, the experience of seeing Kepler launch into space, see it arch through the sky and disappear into orbit, that was wonderful, as was listening to the radio signals when it was going to eject its cover. The telescope is launched into orbit with a cover across the lens. And everybody's sitting there in the control room two weeks l