%0 Journal Article
%T An ancient extrasolar system with five sub-Earth-size planets
%A T. L. Campante
%A T. Barclay
%A J. J. Swift
%A D. Huber
%A V. Zh. Adibekyan
%A W. Cochran
%A C. J. Burke
%A H. Isaacson
%A E. V. Quintana
%A G. R. Davies
%A V. Silva Aguirre
%A D. Ragozzine
%A R. Riddle
%A C. Baranec
%A S. Basu
%A W. J. Chaplin
%A J. Christensen-Dalsgaard
%A T. S. Metcalfe
%A T. R. Bedding
%A R. Handberg
%A D. Stello
%A J. M. Brewer
%A S. Hekker
%A C. Karoff
%A R. Kolbl
%A N. M. Law
%A M. Lundkvist
%A A. Miglio
%A J. F. Rowe
%A N. C. Santos
%A C. Van Laerhoven
%A T. Arentoft
%A Y. P. Elsworth
%A D. A. Fischer
%A S. D. Kawaler
%A H. Kjeldsen
%A M. N. Lund
%A G. W. Marcy
%A S. G. Sousa
%A A. Sozzetti
%A T. R. White
%J Physics
%D 2015
%I arXiv
%R 10.1088/0004-637X/799/2/170
%X The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations. We use asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that Kepler-444 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, leaving open the possibility for the existence of ancient life in the Galaxy. The age of Kepler-444 not only suggests that thick-disk stars were among the hosts to the first Galactic planets, but may also help to pinpoint the beginning of the era of planet formation.
%U http://arxiv.org/abs/1501.06227v1