An international team of astronomers headed by Dr Tiago Campante of the University of Birmingham’s School of Physics and Astronomy, UK, has discovered an extremely ancient extrasolar system with five sub-Earth-size planets.
This is an artistic impression of the Kepler-444 planetary system. Image credit: Tiago Campante / Peter Devine.
Kepler-444 is a metal-poor Sun-like star located in the constellation Lyra, 116.4 light-years away.
Also known as HIP 94931, KIC 6278762, KOI-3158, and LHS 3450, this pale yellow-orange star is very bright and can be easily seen with binoculars.
It was formed 11.2 billion years ago, when the Universe was less than 20 percent its current age. It is approximately 25 percent smaller than the Sun and substantially cooler.
The star hosts a compact multi-planetary system of five exoplanets with sizes between those of Mercury and Venus.
“This is the oldest known system of terrestrial-sized planets in our Milky Way Galaxy – two and a half times older than the Earth,” the astronomers said.
The five planets – labeled Kepler-444 b, c, d, e and f – orbit their host star in less than 10 days or, equivalently, at less than one-tenth Earth’s distance from the Sun.
They were detected from the dimming that occurs when they transit the disc of Kepler-444.
“Long, uninterrupted observations are necessary to observe the weak pulsations. Only with the exquisite, high quality data from the Kepler mission has this been possible,” said Dr Timothy White of the University of Göttingen’s Institute of Astrophysics, who is the senior author of a paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).
“There are far-reaching implications for this discovery. We now know that Earth-sized planets have formed throughout most of the Universe’s 13.8 billion year history, which could provide scope for the existence of ancient life in the Galaxy,” said Dr Campante, who is the first author of the paper.
“By the time the Earth formed, the planets in this system were already older than our planet is today.”
“This is one of the oldest systems in the galaxy. Kepler-444 came from the first generation of stars. This system tells us that planets were forming around stars nearly 7 billion years before our own Solar System,” said co-author Prof Steve Kawaler of Iowa State University.
“This discovery may now help to pinpoint the beginning of what we might call the era of planet formation,” Dr Campante concluded.
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Campante T. L. et al. 2015. An ancient extrasolar system with five sub-Earth-size planets. ApJ, accepted for publication; arXiv: 1501.06227
