Evidence of an apocalypse in a planetary system similar to our own has been uncovered by astronomers studying a dying star.
The shredded remains of a watery asteroid suggest that hundreds of millions of years ago the system may have harboured Earth-like habitable planets.
But any intelligent beings there must have departed – assuming they mastered space travel – or been extinguished as their sun blew up and then collapsed into a “white dwarf”.
Scientists believe six billion years from now, alien astronomers studying the burned out remains of our sun may come to the same conclusion.
Like the white dwarf GD 61, the sun is destined to end its life by expanding into a “red giant” then shedding its outer layers and contracting into a super-dense glowing ember just a few thousand miles in diameter. The dying sun will radiate what is left of its heat over billions of years then finish its life as a dead, cold “black dwarf”.
Astronomers studying the light emitted by GD 61, 150 light years from Earth, detected abundant “rocky” elements such as magnesium, silicon and iron.
They also found oxygen that indicated a very large amount of water. Only a water-rich massive asteroid, or minor planet, can explain the observations.
The giant rock, at least 90km (56 miles) in diameter, would have been drawn in by the white dwarf’s powerful gravity and ripped apart.
Dr Jay Farihi, of Cambridge University, said: “The finding of water in a large asteroid means the building blocks of habitable planets existed – and maybe still exist – in the GD 61 system, and likely also around substantial number of similar parent stars. These water-rich building blocks, and the terrestrial planets they build, may be common – a system cannot create things as big as asteroids and avoid building planets, and GD 61 had the ingredients to deliver lots of water to their surfaces.”
In its heyday, before becoming a white dwarf 200million years ago, the star had about three times the mass of the sun.
The astronomers believe giant planets similar to Jupiter and Saturn may still survive in the outer reaches of its system. Their gravity probably upset the asteroid’s orbit and nudged it close enough to the white dwarf to be shredded.
“This supports that the star originally had a full complement of terrestrial planets, and probably gas giant planets orbiting it – a complex system similar to our own,” said Dr Farihi.