Dying planets hint at earth's future
Paris - The remains of two planets closely orbiting a dying star some 3 900 light years away have given astronomers a glimpse of what may happen at the demise of our own solar system about five billion years from now.
Named KOI 55.01 and KOI 55.02, the planets orbit a sun that has passed the "red giant" stage - a star that has burned up most of its fuel and becomes larger and larger, according to the study, published in the journal Nature on Wednesday.
The pair are respectively 76% and 87% the size of the Earth, but were probably many times larger.
They are likely be the remnants of "gas giant" planets that were roasted by the bloating star's fiery envelope, say the authors.
"KOI 55.01 and KOI 55.02 lie in very close orbits to their host star," said investigator Gilles Fontaine, a professor of astrophysics at the University of Montreal in Canada.
"To be at such a small distance from their giant star, they probably plunged deep into its gas envelope but survived despite the extreme temperature."
The study was published just a day after astronomers reported spotting the first Earth-sized planets in the 16-year-old quest to locate worlds behind the solar system.
At the end of its life, our star could expand as far as Mars, according to some calculations.
"When our sun swells up to become a red giant it will engulf the Earth," said Elizabeth Green of the University of Arizona's Steward Observatory.
"If a tiny planet like the Earth spends a billion years in an environment like that, it will just evaporate. Only planets with masses very much larger than the Earth, like Jupiter or Saturn, could possibly survive."
The new finds were made by the US orbital telescope Kepler, a $600m mission which monitors more than 150 000 stars for tiny wobbles in light.
These fluctuations are interpreted as potentially signalling a planet which is passing in front of the star and is thus dimming the light reaching the telescope.