The Kepler mission, launched 7 March 2009, has been a huge success for NASA. But yesterday one of its four reaction wheels failed and, coupled with a similar failure in another wheel last year, the chances of it continuing operations are in the balance. We spoke to Project Scientist on the Kepler mission Dr. Steve Howell about whether we can recover it, what the mission has taught us and what planet hunting will be like after Kepler.
What are the reaction wheels?
“Kepler, like almost every spacecraft, points to a position in the sky using these things called reactions wheels. They’re devices that are about the size of an American dime, very small little wheels, but they spin at a high rate and because you’re in space you can use these wheels to move the telescope in different directions and keep it pointed very precisely. And Kepler was launched with four of those like most spacecraft.”
So what’s gone wrong?
“One of those reaction wheels failed in July of last year, and a second one appears to have failed two days ago. So right now what that means is that Kepler is in this sort of holding pattern out in space, what we call a safe mode pattern, and it’s just sort of sitting there using its thrusters to keep it from going crazy or rolling or tumbling or something. But we have to asses what’s going on with these reaction wheels, see if there’s a possibility of maybe restarting the one that died last year. We just don’t know what the options are. Unfortunately, without those reaction wheels it’s unlikely that we’ll be able to point the telescope incredibly precisely, which is what we need for most of the work we do.”
How likely is it that Kepler can be saved?
“Well, we don’t really know. When the wheel failed last summer we just immediately turned it off because we had three good wheels left and at that time we didn’t need it, so we didn’t really spend a lot of time investigating what the apparent failure was. So it could be that we can run it at a higher torque, we can put more power into it, or we could run it in the other direction if it helps or something like that, we just don’t really know. The jury is still about 50-50 whether there is any shot at restarting that wheel, so we’ll just have to wait and see.”
What’s the mood like on the team at the moment?
“You know, it’s been a real mixed bag. We clearly are sad at the loss and we’ve all been bemoaning that we had great hopes for more data and all that, but at the same time we have to celebrate the success and we have to look at the fact that it’s been a great mission even if Kepler does nothing more. And yet we still have more to do, we know that there’s a goldmine of information that we’re going to get from the data we have. So it’s been a mixed couple of days.”
How big of a loss will it be if Kepler can’t be saved?
“It’s certainly a loss in that the data collection part of Kepler itself as a telescope will probably be over. Even if there’s some sort other repurposing we can do to the telescope it’s very unlikely the science data will be of the same high quality we need to find very small planets around other stars. So that part is definitely a loss. However, at the same time we have to remember that we have so much data already, and we also have about a year and a half of data that we haven’t even looked through yet. So if it turns out we can’t get any more data from Kepler we can concentrate on the data we have in hand and we have another year or two of work just to plow through all that.”
Can Kepler be replaced?
“That’s a question lots of people have asked. When a space mission eventually dies somehow, all the people that loved that mission say ‘just build another, we know it works!’ But NASA doesn’t work that way and I think there’s a good reason for that. Kepler’s been a great success, it was a mission to find whether planets, especially small ones, are common or not, and so far we know already from the data we have that small planets are everywhere. Most stars have planets and most of these planets are small planets. So the next step is to work out if we can actually learn more about these planets now, can we characterise them and find ones that are very close to our Solar System in astronomy terms. So NASA will move on to other mission and the scientists will want to move on to other science.”
What other missions will we be seeing in the next few years?
“They’re working now on a mission called TESS [Transiting Exoplanet Survey Satellite], and that mission will basically do transit photometry like Kepler but will look at very nearby stars, things that are a few tens of light-years from Earth. I know that still sounds far, but Kepler’s typical planet is 1,000 light-years or more. So these are relatively nearby stars and planets that the next mission will find. And then there will be planets that the JWST [James Webb Space Telescope] can possibly get an image of or information about saying oh, it has an atmosphere, it has oxygen in its atmosphere, things like that. So it’s a progression, and Kepler’s certainly been a great first step, but building another Kepler is not going to happen.”
Images courtesy of NASA and the Kepler team