A Quarter of Sun-Like Stars Host Earth-Size Worlds 105
astroengine writes "Although there appears to be a mysterious dearth of exoplanets smaller than Earth, astronomers using data from NASA's Kepler space telescope have estimated that nearly a quarter of all sun-like stars in our galaxy play host to worlds 1-3 times the size of our planet. These astonishing results were discussed by Geoff Marcy, professor of astronomy at the University of California, Berkeley, during a talk the W. M. Keck Observatory 20th Anniversary Science Meeting on Thursday. '23 percent of sun-like stars have a planet within (1-2.8 Earth radii) just within Mercury's orbit,' said Marcy. 'I'll say that again, because that number really surprised me: 23 percent of sun-like stars have a nearly-Earth-sized planet orbiting in tight orbits within 0.25 AU of the host stars.'"
Re:But... (Score:5, Interesting)
Well, we do have Mercury and Venus in our system and that hasn't hurt us, has it? (Yeah, Mercury is small, but Venus is also on the too-close side even without greenhouse gases and almost Earth-size.)
I guess the point with Kepler is still that due to the methodology (repeated occlusions), shorter orbital periods will increase the chance of detection (more data points to establish significance), in addition to the fact that a planet closer to its host star will occlude a larger area and thus give a stronger signal. Just keeping Kepler going will increasingly shift the distribution of detected planets towards higher star-planet distances. The minimum detectable size will be more or less of a constant function of that distance, though, although again I guess repeated observations can sometimes bring out something that would otherwise be just at the noise floor.
For reference, Kepler has just completed 4 years of operation, but actual planet detection only started on May 12 2009. If you want three confirmed events, you could per definition not yet have detected e.g. an exo-Mars. It simply hasn't passed by three times yet. If the orbital plane is different, the planet might not pass in our line of sight every time, and then working out the period and get a detection can take even longer.
Just wait and see.
Streetlight effect? (Score:4, Interesting)
Re:But... (Score:3, Interesting)
You might want to throw Europa in there. Not a planet, and not in the Goldilocks Zone - but it's close enough to the right size, and tidal forces contribute enough heat to possibly put it in a 'Goldilocks Emeritus' category.