An ancient extrasolar system with five sub-Earth-size planets

• 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, Aguirre, V. Silva, 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: Journal Article
• Language: English
• Published: 26-01-2015
• Subjects: Physics - Earth and Planetary Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.1501.06227

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.