Blinded Kepler: All is not lost

NASA’s planet-spotter may be irreparably damaged but the data it has collected will be of use for years to come. Jonathan Nally reports.

One planet Kepler found (artist’s impression) has two suns, inviting comparison with Tatooine, Luke Skywalker’s home in Star Wars. – NASA/JPL-Caltech/R. Hurt

All is not lost, despite the disappointing news that NASA’s Kepler spacecraft – commissioned to search for Earth-like planets in deep space – may be irreparably crippled, its telescope effectively useless.

Scientists say there is such a large backlog of data from the mission that they will be kept busy for years, sifting through all of the numbers in search of more planets. The planet-hunter has so far detected 3,126 candidate planets, with more than 130 already confirmed.

Launched on 7 March 2009, Kepler’s main job has been to work out what proportion of stars, particularly Sun-like stars, are likely to have Earth-sized planets in “Goldilocks zone” orbits – not too cold, not too hot, but just the right distance from their parent stars for liquid water to exist on their surfaces.

To find these planets, the US$600 million observatory has been staring fixedly at a star-filled patch of our Milky Way galaxy, its sophisticated sensors continually measuring the brightness of more than 100,000 stars, looking for the tell-tale dimming blips when planets move in front of them.

Because it has to gaze non-stop at the same patch of sky, it needs a very accurate orientation system. While some spacecraft use rocket thrusters to change or maintain their position, Kepler uses electric-powered reaction wheels – spinning, gyroscope-like devices. The spacecraft needs three wheels to keep it oriented correctly. It carries one spare wheel, but two have now failed. So, unless one of the faulty wheels can be restarted, the mission’s data-collection phase will be over.

Kepler has had a profound impact on the search for new worlds.

Mission managers have not given up hope of restoring function to one of the failed wheels. “Like any stuck wheel, we could try jiggling it, commanding it back and forth in both directions, or we could try forcing it through whatever the resistance is that’s holding it up,” says Charlie Sobeck, Kepler’s deputy project manager at NASA’s Ames Research Center.

Kepler has had a profound impact on the search for new worlds.

“It has identified examples of Earth-sized planets orbiting Sun-like stars in habitable-zone orbits,” says Professor Chris Tinney, deputy director of the Australian Centre for Astrobiology and leader of the Anglo-Australian Planet Search program. “So by those measures it has found that the Earth is not in a unique environment.”

In any case, Kepler has performed for longer than planned. It was designed to spend three-and-a-half years on its planet search, but last year the mission was extended until 2016. The reaction wheel problem has occurred at just over the four-year mark.

And the hunt for extraterrestrial life is not dependent on just one space observatory. Kepler was always intended to be the forerunner to a new generation of space telescope, one that can home in on the kinds of worlds Kepler has found. Whereas Kepler’s role has been to define whether Earth-sized planets exist, the new kind of telescope – a “terrestrial planet finder” – will give us detailed information about them.

Paul Davies, professor of physics at Arizona State University, points out that finding a planet with the potential for life is a far cry from finding life itself.

The Kepler spacecraft was fitted with four gyroscope-like devices to keep it pointing in the right direction. It needs three to function but two have now failed. – NASA

According to Davies, the unknowns about how life emerges is “the elephant in the room” and overshadows the statistics of planet discovery.

“If the probability of the transition to life is, say, one in a trillion trillion per billion years per planet, then it is completely irrelevant whether there are one billion or two billion Earth-like planets in the Milky Way, because there will still be a vanishingly small chance of another planet with life,” Davies says.

By the same token, if the transition to life has a higher probability, there could be millions of inhabited planets.

Nevertheless, Davies readily agrees that Kepler’s planet discoveries have given us a huge head start on the road to determining whether life exists elsewhere in the Galaxy.

“It has propelled the subject to the forefront of the astrobiology agenda,” he says.

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