An Earth-sized planet with an Earth-like density
Abstract
Kepler-78 (KIC 8435766) was identified by Sanchis-Ojeda et al. (2013) as harbouring a transiting planet of 1.16 times the size of the Earth and an orbital period of only 8.5 hours. While the exquisite Kepler photometry was able to determine its radius and period, the mass of the planet (and thus its mean density) remained unconstrained in the absence of precise radial-velocity measurements. Here we present an accurate mass measurement of Kepler-78b using the HARPS-N spectrograph, recently installed on the Telescopio Nazionale Galileo (INAF) at the Roque de los Muchachos Observatory, La Palma, Spain. These new data yield a mass of 1.86 Earth masses. The resulting mean density of the planet is 5.57 grams per cubic centimetre, which is similar to that of the Earth and implies a composition of iron and rock. Kepler-78b, which orbits a Sun-like star called Kepler 78 located in the Cygnus constellation at a distance of about 400 light years from us, is now the smallest exoplanet for which both the mass and radius are known accurately.
Cite
@article{arxiv.1310.7987,
title = {An Earth-sized planet with an Earth-like density},
author = {Francesco Pepe and Andrew Collier Cameron and David W. Latham and Emilio Molinari and Stéphane Udry and Aldo S. Bonomo and Lars A. Buchhave and David Charbonneau and Rosario Cosentino and Courtney D. Dressing and Xavier Dumusque and Pedro Figueira and Aldo F. M. Fiorenzano and Sara Gettel and Avet Harutyunyan and Raphaëlle D. Haywood and Keith Horne and Mercedes Lopez-Morales and Christophe Lovis and Luca Malavolta and Michel Mayor and Giusi Micela and Fatemeh Motalebi and Valerio Nascimbeni and David Phillips and Giampaolo Piotto and Don Pollacco and Didier Queloz and Ken Rice and Dimitar Sasselov and Damien Ségransan and Alessandro Sozzetti and Andrew Szentgyorgyi and Christopher A. Watson},
journal= {arXiv preprint arXiv:1310.7987},
year = {2013}
}
Comments
10 Pages, 8 figures, 5 tables, data. Nature, 2013 (published online Oct. 30)