Blue moons? Kepler-22b offers NASA habitable world hopes
— -- Star Wars toured "Tatooine," Star Trek visited "Vulcan" and Avatar plundered "Pandora."
And NASA? NASA's Kepler space telescope team this month unveiled "Kepler-22b." A planet some 600 light-years away, Kepler-22b circles its star squarely in a "habitable zone" — the orbital distance where a world's surface temperature would neither boil nor freeze water, perhaps allowing oceans to survive as on Earth. Water is widely seen as one of life's vital ingredients by planetary scientists.
Catchy names, clearly, aren't a priority in astronomy. Other proposed habitable zone worlds reported by astronomers (among the more than 700 planets detected in the last two decades orbiting nearby stars) sport monikers such as "55 Cancri f" and "HD 85512 b.
But at least some solace comes from the Kepler space telescope team's estimate that just in our Milky Way galaxy alone, some 500 million planets likely orbit inside their star's habitable zone.
"We have many candidates in that region," said Kepler principal scientist William Borucki of NASA's Ames Research Center in Moffett Field, Calif., at a briefing unveiling Kepler-22b to his colleagues earlier this month. At his briefing, Borucki showed a chart depicting more than 50 possible habitable zone planets, as well as Kepler-22b, among the 2,326 planetary candidates detected by Kepler since its 2009 launch.
How has Kepler piled up so many planet candidates? The $591 million space telescope gazes unblinkingly at roughly 170,000 stars within 3,000 light years (one light year is about 5.9 trillion miles) along the " Orion Spur" of stars in our Milky Way. Kepler detects planets by spotting dips in starlight, eclipses called "transits," that they cause when they circle in front of their stars.
Science fiction fans hoping that Kepler-22b is another Earth may need the solace that many more habitable planets may be out there. That's because the early indications are that Kepler-22b's habitable zone isn't all that habitable for that particular world.
For one thing, Kepler-22b isn't really Earth-like. At 2.4 times the width of Earth, Kepler-22b seems more like a smaller version of the gas-shrouded world Neptune in our own solar system, according to planet hunter Geoff Marcy of the University of California, Berkeley. Where Neptune is about 17 times heavier than Earth, Kepler 22b is likely about 14 times heavier than Earth, estimates astronomer Francesco Pepe of Switzerland's Geneva Observatory, who attended the Kepler briefing. At that weight, Kepler-22b likely has an atmosphere nothing like Earth, likely making it uninhabitable.
The Kepler team for example estimated that Kepler-22b, if it had an atmosphere like Earth's, would enjoy balmy average temperatures of 72 degrees Fahrenheit, "a little warmer than a nice day here in California," Borucki said. But even the draft paper written by Borucki and colleagues describing the discovery admits this is "not very likely."
