SEATTLE — NASA’s prolific Kepler Space Telescope may get to extend its search for exoplanets by a few years.

Funding for Kepler — which has identified more than 1,200 candidate alien planets to date and recently discovered the first exoplanet with two suns in its sky — is due to run out in November 2012. But mission managers are writing a proposal for a mission extension, and they should know by next spring whether it is approved.

“I think the discoveries we’re making are showing what could be done if we continue to extend it,” said Charlie Sobeck, Kepler deputy project manager at NASA’s Ames Research Center in Mountain View, Calif. “So we’re hopeful, but there’s no guarantee.”

It would cost about $20 million per year to keep the Kepler mission running at its current level of activity beyond November 2012, Sobeck added.

The $600 million Kepler observatory launched in March 2009 aboard a United Launch Alliance Delta 2 rocket. Its mission is to find roughly Earth-size planets in or near the habitable zones of their parent stars — a just-right range of distances that could support liquid water and perhaps life.

Kepler’s overall goal is to help scientists determine just how common such planets may be throughout our galaxy.

Kepler finds alien planets using what is called the transit method. The telescope detects the telltale dips in brightness caused when an alien planet crosses in front of, or transits, its star from Kepler’s perspective. Kepler needs to witness three of these transits to firmly identify a planet candidate.

This technique has been extremely effective. In just its first four months of operation, Kepler discovered 1,235 exoplanet candidates. So far, two dozen of them have been confirmed by follow-up observations — including Kepler-16b, a world with two suns that was announced recently. Kepler team members have estimated that 80 percent or so of the telescope’s candidates will probably end up being confirmed as planets. If that is the case, Kepler’s finds to date would more than double the number of known alien planets, which currently stands at about 685.

The Kepler discoveries are about much more than just adding to the total exoplanet count. The telescope’s main task, after all, is to help scientists determine just how many potentially habitable, Earth-size alien planets may be out there.

Of those first 1,235 planet candidates, 68 are roughly Earth-size and 54 appear to orbit in their stars’ habitable zones. And five candidates meet both of those criteria.

“What we’re seeing is this trend — the smaller the planet, the more of them there are,” Sobeck said. “That’s great news for the idea of finding Earth-like planets, or Earth-size planets. Once you have Earth-size planets, all it has to do is be in the right orbit, and it’s habitable.”

Kepler’s discoveries have also opened astronomers’ eyes to the incredible diversity of alien planets and solar systems. For example, the mission has detected one world as dense as iron (Kepler-10b) and another as light and airy as styrofoam (Kepler-7b). And it found one solar system (Kepler-11) whose six known planets all orbit closer to their star than Venus does to the sun.


Keeping the lights on

When Kepler launched in 2009, the telescope’s science mission was set to run through November 2012 — a lifetime of 3.5 years. But the Ball Aerospace & Technology-built spacecraft could operate for six years, or perhaps longer, if it receives more funding, team members have said.

Giving Kepler more time to search for extrasolar planets could yield big dividends for several reasons, researchers said. Because of the three-transit requirement, most of the worlds Kepler has found to date zip around their stars relatively quickly, in close-in orbits. But keeping Kepler going for another few years would give it a chance to look for planets in more distant orbits, allowing the telescope to survey the habitable zones of warmer stars. Seeing more transits would also increase the signal-to-noise ratio for closer-in planets, allowing more of them to be detected, researchers said.

The Kepler team plans to submit its extension proposal to NASA headquarters in January, Sobeck said. He expects an answer by April or May.

If Kepler is extended, exactly how much money the mission would get depends on what NASA wants it to do, Sobeck added. The mission currently costs about $20 million per year to operate.

That may not seem like much, especially since the space agency has already invested about $600 million into the planet-hunting mission. But Sobeck realizes that every dollar is precious in these tough economic times, so he and the Kepler team are not taking anything for granted.

“The budget is simply very tight everywhere,” Sobeck said. “Kepler is a wonderful mission. It has a lot of support at headquarters as well as in the community, but so do other missions.”

But some researchers stress that the tough budget environment strengthens the case for re-upping Kepler.

“In budget-tightening times, you want to get the very best value for your money,” said astronomer Greg Laughlin of the University of California, Santa Cruz. “And a great way to get value for your money is to extend missions that are working beautifully and which have a team in place, and which have basically zero risk.”

Kepler is just such a mission, Laughlin said.

“It would seem to me just nuts to have it out there and turn it off,” he said. “If we as a nation can’t manage to keep the lights on on Kepler, it’s a little disconcerting and disheartening.”