KOI-3158: The oldest known system of terrestrial-size planets

• Published in: EPJ Web of Conferences 2015-01, Vol.101, p.2004-1-02004-4
• Main Authors: Campante, T. L., Barclay, T., Swift, J. J., Huber, D., Adibekyan, V. Zh, Cochran, W., Burke, C. J., Isaacson, H., Quintana, E. V., Davies, G. R., Silva Aguirre, V., Ragozzine, D., Riddle, R., Baranec, C., Basu, S., Chaplin, W. J., Christensen-Dalsgaard, J., Metcalfe, T. S., Bedding, T. R., Handberg, R., Stello, D., Brewer, J. M., Hekker, S., Karoff, C., Kolbl, R., Law, N. M., Lundkvist, M., Miglio, A., Rowe, J. F., Santos, N. C., Van Laerhoven, C., Arentoft, T., Elsworth, Y. P., Fischer, D. A., Kawaler, S. D., Kjeldsen, H., Lund, M. N., Marcy, G. W., Sousa, S. G., Sozzetti, A., White, T. R.
• Format: Article
• Language: English
• Subjects: Earth; Extrasolar planets; Galaxies; Mercury (planet); Metallicity; Planet detection; Planet formation; Planets; Solar system; Stars; Stellar age; Stellar seismology; Terrestrial planets; Universe; Venus
• ISSN: 2100-014X; 2101-6275; 2100-014X
• DOI: 10.1051/epjconf/201510102004

The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe’s history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts five planets with sizes between Mercury and Venus. We used asteroseismology to directly measure a precise age of 11.2 ± 1.0 Gyr for the host star, indicating that KOI-3158 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, providing scope for the existence of ancient life in the Galaxy.