Two Earth-sized planets orbiting Kepler-20

Fressin, Francois and Torres, Guillermo and Rowe, Jason F. and Charbonneau, David and Rogers, Leslie A. and Ballard, Sarah and Batalha, Natalie M. and Borucki, William J. and Bryson, Stephen T. and Buchhave, Lars A. and Ciardi, David R. and Desert, Jean Michel and Dressing, Courtney D. and Fabrycky, Daniel C. and Ford, Eric B. and Gautier, Thomas N. and Henze, Christopher E. and Holman, Matthew J. and Howard, Andrew and Howell, Steve B. and Jenkins, Jon M. and Koch, David G. and Latham, David W. and Lissauer, Jack J. and Marcy, Geoffrey W. and Quinn, Samuel N. and Ragozzine, Darin and Sasselov, Dimitar D. and Seager, Sara and Barclay, Thomas and Mullally, Fergal and Seader, Shawn E. and Still, Martin and Twicken, Joseph D. and Thompson, Susan E. and Uddin, Kamal (2012) Two Earth-sized planets orbiting Kepler-20. Nature, 482 (7384). pp. 195-198. ISSN 0028-0836


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 ⊕ •), and hence has 2.9 times its volume. Here we report the discovery of two planets, one Earth-sized (1.03R ⊕ •) and the other smaller than the Earth (0.87R ⊕ •), 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.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Files associated with this item cannot be displayed due to copyright restrictions.
Faculty / Department / School: No Faculty
Date Deposited: 03 Jul 2017 06:32
Last Modified: 04 Jul 2017 03:30
Uncontrolled Keywords: extrasolar planets; exoplanets; Kepler; photometry; spectroscopy; radial velocity
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020102 Astronomical and Space Instrumentation
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1038/nature10780

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