Earth-sized planets in Milky Way hint at ancient life

Five planets transiting a larger primary star about 117 light years from Earth may constitute the oldest known system of terrestrial-sized planets, scientists say.
The discovery hints at the possibility of ancient life elsewhere in our galaxy, researchers said.
Dr Tiago Campante, an Asteroseismology Research Fellow at the University of Birmingham (UK) who led the research team, focused on a system of five terrestrial-sized planets observed by the Kepler space telescope transiting the star KOI-3158, about 117 light years from Earth in the constellation Lyra.
KOI-3158 is the closest and brightest multi-planet system detected so far by Kepler, said Campante.

The star system is estimated to be 11.2 billion years old, give or take 900 million years or so "which makes KOI-3158 the oldest known system of terrestrial-size planets," Campante told a symposium in France earlier this year.
In contrast, our own Sun and solar system is believed to be less than 5 billion years old.

The planets circling KOI-3158 are also familiar in terms of their size, with the innermost being about the size of Mercury, followed by three Mars-sized intermediate planets and a fifth and largest planet that is bigger than the other four, but a bit smaller than Venus.

Campante noted that KOI-3158 is an iron-poor star, and that stars hosting small planets tend to be more diverse in terms of their chemical composition than stars hosting giant planets, which tend to be metal-rich, 'Gizmag' reported.
"That implies that Earth-sized planets may have readily formed at earlier epochs in the universe's history when metals were more scarce," he said.
"KOI-3158, a system of terrestrial-sized planets, formed when the universe was less than 20 per cent of its current age, so that suggests that Earth-sized planets may have formed throughout most of the universe's history, leaving open the possibility for the existence of ancient life in the galaxy," he added.

The findings have been submitted for publication in The Astrophysical Journal.