Kepler could get a new lease of life

NASA’s champion planet-hunter, which recently suffered a fatal breakdown, is now looking on the sunny side. Despite the loss of its precision steering capability earlier this year, the Kepler space telescope may be able to hunt for planets once more, using a helpful push from the sun.

Engineers behind Kepler discussed the plan, dubbed K2, at the Kepler Science Conference II at the NASA Ames Research Center in Moffett Field, California, this week.

K2 will look at a much larger section of the sky than Kepler’s original mission – potentially capturing a bigger diversity of planets. It won’t be able to stare at the same patch of sky for as long, so K2 will be restricted to hunting for planets that orbit their stars much more closely than Earth does the sun. However, in the cases when such stars are cooler than the sun, some of these could still host life.


“There have been people saying ‘game over’,” says Natalie Batalha, one of the scientists on the Kepler team. “I think it’s very premature to say that.”

Sunlight spin

Kepler was designed to stare intently at a single patch of the sky for years on end. It hunted for planets by measuring the brightness of the stars in its field of view to exquisite precision.

When planets passed in front of those stars, Kepler noticed them dim slightly. Since its launch in 2009, the space telescope’s vigil has paid off with a haul of more than 3500 possible exoplanets. The existence of some of these are confirmed, others are still classed as candidate planets, but the results point to a Milky Way teeming with potentially habitable worlds.

To do that patient work, Kepler needed to be able to point at the same patch of sky without interruption. In late 2012, one of the four reaction wheels that hold it steady failed. It managed to carry on for a while, because only three are needed, but when a second wheel failed earlier this year, it spelled the end of Kepler’s original mission.

Kepler can still point at any location in the sky, but it can’t control its own rotation. Sunlight falling on the craft gives it a tiny push, and when that sunlight falls on the craft unevenly, it can set the telescope spinning.

Whizzy planets

“If we could turn off the sun, then we could probably go back and point at the Kepler field of view and stay perfectly stable. We could do what we needed to do,” says Charlie Sobeck, the Kepler deputy project manager. “Because Kepler is out in the middle of nowhere, the only disturbance we have is the solar pressure.”

Now, rather than turning off the sun, the Kepler team has devised a way to keep the telescope from spinning. They have found a way to manoeuvre the craft into a position that should keep the amount of sunlight falling on both sides relatively even.

“It’s like balancing a pencil on your finger. As long as you can keep that pencil balanced with your finger below, it’s not going to tip over,” says Sobeck.

However, the team says they could only observe the same patch of sky with this method for two or three months at a time before they would have to shift position again to keep the sulight from entering Kepler’s field of view and blinding it.

Because Kepler needs to see a planet pass in front of its star at least three times in order to make a discovery, this frequent shifting will limit Kepler to spotting planets that take just 20 to 30 days to whizz around their host stars.

Cooler than Mercury

Such speedy planets would be huddled closer to their parent stars than Mercury, which takes 88 days to go around the sun. But they need not roast like Mercury does. Around dim red dwarf stars, planets this close can lie within the habitable zone – the region around the star where temperatures allow liquid water to exist.

The constant shifting will also let Kepler view more of the sky. “We’re opening the doors to some very different kinds of science, a much bigger section of the sky, a more diverse set of target stars to look at,” says Sobeck. “There are things that we can do in K2 that we never had an opportunity to look at before in the Kepler field of view.”

Since its breakdown, there have been other suggestions for how to give Kepler a new lease of life but this is the one that the team has decided to ask NASA to fund.

The K2 proposal still needs to work its way through the NASA funding evaluation process before the new mission can start in full. But preliminary tests of the new steering method are already under way, and are likely to continue into early 2014. If those tests go well, the Kepler telescope may have years of planet hunting to come.