Are you still working on the Kepler mission, even though it has been crippled by reaction-wheel blowouts that left it unable to hunt for more new worlds?
The spacecraft is not taking data anymore, but we're still working on analyzing the second half of the data. There are still discoveries to be made out of the data, and lots of work to doto follow up and confirm the [planetary] candidates using ground-based telescopes, and to measure the mass and the radius of each candidate. That's the most important work. If you can measure the size and mass, then you have the density, and then you can tell whether it's a rocky planet, or a lower-density water world, or something with even lower-density like the ice giants Uranus and Neptune.
Now that Kepler's hobbled, does that increase the importance of the TESS mission?
TESS is the next logical step either way. Now that we know the planets are out therethat's the real scientific revolution of Keplerwe can begin followup experiments. When we proposed Kepler, we didn't know whether planets would be very common or extraordinarily rare. Now we know that planets are common and the chances are that we're not alone. There are so many planets out there now we've just got to find the ones that show signs of life.
How will TESS build on Kepler's discoveries?
The key here is that TESS is an all-sky survey. Kepler only looks at 1/400 of what TESS will see. We're going to follow light over the whole sky, but we won't spend as long looking at each locationonly about a month at a time. If we spot interesting candidates, we can maybe follow up later.
TESS will look at stars that are nearer and brighter than the ones Kepler is studying. We haven't been able to get the masses of most of the exoplanets Kepler found because they're too far away for ground-based telescopes to measure. The key is getting both the size and the mass so you can learn the density, and TESS opens that door because it looks at the nearest and brightest, where we can follow up with ground-based telescopes.
How will TESS do all this on a small budget?
TESS is scrappier than Kepler, and we're proud of that. Kepler was more expensive than it needed to beit cost $640 million at launchwhereas we have a cost cap of $200 million. We've learned an enormous amount from Kepler, and it's given us a lot of ideas.
TESS has a special orbit called a lunar resonant orbit. It's an elongated orbit that goes out past the moon, then passes quite close to Earth. It gives us continuous monitoring of the targets, and when it gets close to Earth, we can transmit data much more efficiently than Kepler did.
Another thing is that an enormous amount of work went into developing the pipeline for processing the Kepler data. They spent more than 100 man-years developing it. The same team is now going to convert that pipeline into the TESS pipeline. We'll reuse a lot of the code, a lot of the algorithms and ideas behind it. That's an enormous advantage.
What do you hope will come out of the TESS mission?
We really want to find rocky plants that have solid surfaces, and we want to find them at the right distance from their stars so that they have the right temperature for liquid water on their surface. The holy grail would be to identify a fewmaybe one or two or threereally prime candidates. They would be nearby, orbiting stars similar to the sun but smaller, where we can characterize the atmosphere.
And the real dream is that someday we'll detect a molecule in an atmosphere that is a product of lifeor in other words, a biomarker. It's a little tricky, because you've got to pick molecules that can only come from life. It's possible TESS could find something like that, although it might take another 20 years after TESS when we have the right telescopes to do the followup work.
Will TESS be able to look for atmospheres and biomarkers?
TESS is a spotter mission. After we identify the best candidates for rocky planets, it will be big facilities like the James Webb space telescope, or the next generation of giant telescopes from international collaborators, which will be 20 or 30 meters in diameter and cost a billion dollars each. We think we can use those to characterize atmospheres.
Do you think someday soon we'll be able to travel to one of the Earth-like exoplanets that TESS is expected to discover?
Finding them is one thing, but actually going there is a completely different ball game. I'd never say never, but it's not in the foreseeable future. Not with the present economy, or with the present technology. But who knows what will be feasible in 100 years? Even 20 years ago, if you told me we'd be studying the atmospheres of distant planets, I'd have told you to get out of town. But we do it all the time now.
