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Artist's impression of a sunset from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. (ESO/L. Calçada)
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‘Billions’ Of Habitable Worlds In Our Own Milky Way Galaxy?
Wednesday, March 28, 2012 14:40
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Published March 28, 2012
Discovery News
Take the most common type of star in the Milky Way — so-called red dwarf stars that are cooler, smaller and longer-lived than stars like the sun.
Then, survey a sampling for orbiting planets and extrapolate the results. What do you get?
A stunning claim that 40 percent of our galaxy's 160 billion red dwarf stars have plus-sized Earths orbiting the right distance for liquid water to exist on their surfaces, a condition believed to be necessary for life.
ANALYSIS: Red Dwarfs May Be Safe Havens For Life
Study examines the prevalence of planets around red dwarf stars, the galaxy's most common type.
40 percent could harbor planets that maintain water in a liquid state on their surfaces.
But there is no way of knowing how many of these worlds will be rocky, and therefore genuinely "habitable."
The effort is complementary to studies by NASA's Kepler space telescope, which hunts for extrasolar planets around sun-like stars.
About 80 percent of the stars in the Milky Way are red dwarfs, which, on average, are about one-third smaller and 4,000 degrees Fahrenheit cooler than the sun.
Kepler lead scientist William Borucki, with NASA's Ames Research Center in Mountain View, Calif., said he's not surprised by the finding of the European team, which uses a light-splitting spectrograph called HARPS on a telescope at the La Silla Observatory in Chile to look for planets beyond the solar system.
But claiming that red dwarfs' planets are rocky worlds — a condition likely necessary for them to be genuinely "habitable" — goes too far, Borucki told Discovery News.
"I am astounded that they're saying they are rocky planets. I don't see any reason to assume they're rocky planets," Borucki said.
ANALYSIS: Alien Life May Live in Various Habitable Zones
Limits of the technology used by the HARPS team, which looks for slight wobbles in starlight caused by an orbiting planet's gravity, make assessments of a planet's density difficult, if not impossible, to determine. The Kepler team, which finds planets as they pass across their parent star's face relative to the telescope's line of sight, likewise is limited by its technique.
"Each technique has some strengths and some real weaknesses. None of them is perfect. None of them give you all the answers you’d really like to have," Borucki said.
