Did the Kepler planet hunters leak data about other Earths?

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PostThu Jul 29, 2010 10:03 pm » by Savwafair2012


Nature - and the news media, it seems - abhors a vacuum. That could explain the recent uproar over a talk by Dimitar Sasselov, a member of the planet-hunting Kepler space telescope's science team.

Kepler launched in March 2009 and has been hard at work staring at the same patch of sky in search of characteristic dips in starlight that would signal a passing planet. Progress has been fairly quick. Not long after reaching orbit, the telescope team released the vital stats on five confirmed planets and announced it had found 706 stars that seem to have planet potential.


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But NASA has allowed data on 400 of these stars, which include the brightest and easiest to study, to be held back from public release until February 2011. This secrecy has frustrated some astronomers and fuelled a hunger for news of more planets, particularly Earth-like ones.

Enter Sasselov, who presented a talk at a TEDGlobal conference in Oxford on 16 July (you can watch the video here). In his presentation, Sasselov presents a chart (shown above) that suggests Kepler has found about 140 "Earth-like" candidates smaller than two times the radius of the Earth.


That figure is baffling, because it conflicts with the official Kepler results, which turned up just 38 such Earth-sized candidates in the 306 stars that were made public in June.

The talk was quickly picked up by the press and presented as a new discovery. It also took on an air of scandal. Richard Kerr of Science magazine dubbed the presentation a leak. The talk, he said, "was especially striking because it was largely based on Kepler data that team members had been allowed to keep to themselves for further analysis until next February."

Not so, says Sasselov. He says his chart uses the same data that was presented in Kepler's previous announcement, only it has been "rebinned" to include candidates with larger radii, up to 2.9 times the radius of the Earth. The chart label fell victim to TED font size requirements, and the "9" was lopped off instead of being rounded up. "The chart definitely has a mistake," Sasselov told New Scientist.

The larger planet candidates were lumped together with smaller ones to reflect the notion that they are all rocky bodies that could have the potential to harbour life.

But finding such planets in the habitable zones of their stars is still a ways off. None of the small planet candidates that have been reported so far, which come from just 43 days of Kepler data, orbit far enough from their hosts to be habitable.

As a result, none of the 140 or so "Earth-like" planets presented in Sasselov's talk are likely to be pleasant vacation spots.

"The term 'Earth-like' planet creates confusion. To some scientists like me, who model planet interiors, the term 'Earth-like' is a simple short-hand for a bulk composition like Earth's," Sasselov wrote in a blog post on NASA's web site.

"But most people consider the term 'Earth-like' to mean that the planet has an atmosphere, liquid water on its surface, and a temperature conducive to life. In other words, 'Earth-like' is often used to mean 'habitable'," he continued. "Therefore, Earth-size and Earth-like are certainly not the same. Take the example of Venus, an Earth-size planet whose surface will melt lead."

We may not have found them yet, but astronomers do expect to find a number of planets with cosy, Earth-like properties. Hunts for periodic shifts in the spectrum of starlight - which can reveal wobbles due to tugging planets - have shown that planets with radii up to a few times that of Earth are common very close to their stars, where it's too hot for life as we know it to survive. "Because we find a lot of planets on short-period orbits, we expect to find a lot of planets on long-period orbits," says Greg Laughlin of the University of California, Santa Cruz. "It would be extremely surprising if Earth-like planets in the habitable zone were rare."

There may very well be hundreds of millions of potentially habitable rocky planets in the Milky Way, but solid estimates are still a ways off.

The race to find the very first one could well be won by teams looking for wobbling stars rather than dips in starlight, Laughlin says. That's because surveys that look for these wobbles are better suited than Kepler to find planets around small, dim stars. Habitable planets around these puny stars would be on tighter, faster orbits than those around larger stars, making them relatively easy to spot.




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