Francois Fressin, Guillermo Torres, Jason F. Rowe, David Charbonneau, Leslie A. Rogers, Sarah Ballard, Natalie M. Batalha, William J. Borucki, Stephen T. Bryson, Lars A. Buchhave, David R. Ciardi, Jean-Michel Desert, Courtney D. Dressing, Daniel C. Fabrycky, Eric B. Ford, Thomas N. Gautier III, Christopher E. Henze, Matthew J. Holman, Andrew W. Howard, Steve B. Howell, Jon M. Jenkins, David G. Koch, David W. Latham, Jack J. Lissauer, Geoffrey W. Marcy, Samuel N. Quinn, Darin Ragozzine, Dimitar D. Sasselov, Sara Seager, Thomas Barclay, Fergal Mullally, Shawn E. Seader, Martin Still, Joseph D. Twicken, Susan E. Thompson, Kamal Uddin
Since the discovery of the first extrasolar giant planets around Sun-like
stars, evolving observational capabilities have brought us closer to the
detection of true Earth analogues. The size of an exoplanet can be determined
when it periodically passes in front of (transits) its parent star, causing a
decrease in starlight proportional to its radius. The smallest exoplanet
hitherto discovered has a radius 1.42 times that of the Earth's radius (R
Earth), and hence has 2.9 times its volume. Here we report the discovery of two
planets, one Earth-sized (1.03R Earth) and the other smaller than the Earth
(0.87R Earth), orbiting the star Kepler-20, which is already known to host
three other, larger, transiting planets. The gravitational pull of the new
planets on the parent star is too small to measure with current
instrumentation. We apply a statistical method to show that the likelihood of
the planetary interpretation of the transit signals is more than three orders
of magnitude larger than that of the alternative hypothesis that the signals
result from an eclipsing binary star. Theoretical considerations imply that
these planets are rocky, with a composition of iron and silicate. The outer
planet could have developed a thick water vapour atmosphere.
View original:
http://arxiv.org/abs/1112.4550
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