An Ancient Extrasolar System With Five Sub-Earth-Size Planets




Campante, T. L.
Barclay, Thomas
Swift, Jonathan J.
Huber, Daniel
Adibekyan, V. Z.
Cochran, William
Burke, C. J.
Isaacson, Howard
Quintana, Elisa V.
Davies, G. R.

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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 +/- 1.0Gyr 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.



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Campante, T. L., T. Barclay, J. J. Swift, D. Huber, V. Zh Adibekyan, W. Cochran, C. J. Burke et al. "An ancient extrasolar system with five sub-Earth-size planets." arXiv preprint arXiv:1501.06227 (Feb., 2015).