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Watery asteroid discovered 150 light-years off hints at habitable worlds

White dwarf drains juice from small victim

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A European trio of researchers has discovered a "circumstellar disk" – a corpse, in other words – of a minor planet that was about 26 per cent water.

The discovery of the rocky remains, found orbiting a white dwarf star 150 light years over the rainbow, gives credence to the theory that our own Earth's watery condition was brought about when such H2O-bearing rocks – asteroids, planetoids, and the like – crashed into our home world in the distant past.

The boffinry breakthrough is detailed in a paper published in the journal Science titled "Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet".

While those of us on Earth's surface are duly impressed by the vastness of our oceans and seas, our planet is actually rather water-poor. As Phys.org points out, water accounts for only about 0.02 per cent of Earth's mass.

That's a paltry dribble when compared with the 26 per cent of mass estimated to have been in the now-destroyed planetoid that once orbited around its home star, which collapsed into white dwarf GD61 about 200 million years ago.

That 26 per cent, by the way, is essentially equal to the proportion of water in Ceres, the largest asteroid in our solar system's main asteroid belt between Mars and Jupiter.

At 930 kilometers in diameter, however, Ceres is much larger than the now-defunct victim of GD61, which the researchers estimate to have been just 90km or so.

Artist's conception of a watery asteroid being torn apart white dwarf GD 61

Artist's conception of a watery asteroid being shredded (source: Mark A. Garlick, space-art.co.uk)

Despite its formerly small size, the ex-asteroid is tantalizing in a number of ways. First, of course, is its water content. But also of great interest is that it's the first body found outside our solar system that has the two main ingredients needed for life as we know it: a rocky composition and abundant water.

Also of interest is the fact that when GD61 turned into a white dwarf, there was no particular reason why the asteroid, planetoid, or whatever you want to call it – and likely some of its fellow travelers – should have been torn apart by the dwarf's gravitational forces.

Unless it was pushed.

"In order for the asteroids to pass sufficiently close to the white dwarf to be shredded, then eaten," the paper's lead author Jay Farihi told Phys.org, "they must perturbed from the asteroid belt – essentially pushed – by a massive object like a giant planet."

That means that there are other, far more massive bodies that are now orbiting or have orbited GD61, and that at least some of them are or were likely to have the same rocky, watery composition as the object that met its doom in GD61's gravitational maw, or were given water by similar objects, as it appears that the Earth has been.

"Our results demonstrate that there was definitely potential for habitable planets in this exoplanetary system," Farihi said. ®

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