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Confusion Over Kepler's 'Earth-Like' Planets Explained

NASA's mini fiasco in public communication last week was a scientist's attempt at public outreach gone awry. Kepler mission co-investigator Dimitar Sasselov of Harvard University, speaking at the popular TED talks, tried to convey the excitement of hunting for Earth-size planets orbiting in the habitable zones of other stars. But his sloppy terminology and careless graphics, says Kepler Principal Investigator William Borucki, led to headlines that Kepler had just discovered hundreds of Earth-like planets. That's not true, says Borucki of NASA's Ames Research Center in Mountain View, California. "I'm disappointed one of our members confused people."

Sasselov's problems go back to his use of the term "Earth-like" in his 18-minute presentation last month to a conference in Oxford, U.K.

"Kepler cannot tell whether [a candidate exoplanet] is Earth-like or not," notes Borucki. The orbiting telescope determines only an exoplanet's size and, given more observing time, the distance from its star. " 'Earth-like' is a term common among astrophysicists," Borucki adds, "but it's not appropriate for the public."

Compounding the confusion, Sasselov redrew a figure from a Kepler team manuscript and, in the process, inadvertently squeezed the majority of candidate exoplanets into a size category he labeled "like Earth." But "there are no Earth-size planets in my figure," says Borucki, the manuscript's first author. Look for the official release of the Kepler team's analysis of its most promising data next February. NASA's public affairs office should be firmly in control by then.

Update: Sasselov's mea culpa.