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Building Blocks for Earth-Like Planets Found Around Dying Star

Posted October 10, 2013, 10:49 AM HST
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An artist’s impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star GD 61. Image by Mark A. Garlick, space-art.co.uk, University of Warwick and University of Cambridge.

Astronomers studying a dying star 150 light years away have discovered a rocky body with an ample amount of water.

They say the finding marks the first time that the two key ingredients for habitable planets have been found outside of our solar system.

The findings using data collected by both Keck telescopes atop Mauna Kea and NASA’s Hubble Space Telescope and the agency’s FUSE telescope were reported today in the journal Science.

Astronomers at the Universities of Cambridge and Warwick say this is the first “reliable evidence” for water-rich, rocky planetary material in any extrasolar planetary system.

The water was found in the shattered remains of an asteroid orbiting the white dwarf star GD 61.

Analysis of the asteroid indicated it is composed of 26% water mass. Scientists said that is very similar to Ceres, the largest body in the asteroid belt between Mars and Jupiter.

By comparison, Earth has only 0.02% of its mass as surface water. Astronomers say that makes it essentially a “dry” planet, meaning its oceans formed long after it formed – likely the result of water-rich asteroids crashing into our planet.

“The new discovery shows the same water delivery system could have occurred in this distant, dying star’s solar system – as latest evidence points to it containing a similar type of water-rich asteroid that would have first brought water to Earth,” the Keck Observatory said in a statement today.

All rocky planets form from the accumulation of asteroids, growing until full size, so asteroids are essentially the “building blocks” of planets, it 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 a substantial number of similar parent stars,” said Jay Farihi of the Cambridge Institute of Astronomy, the lead scientist on the project.

“These water-rich building blocks, and the terrestrial planets they build, may in fact 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,” Farihi said. “Our results demonstrate that there was definitely potential for habitable planets in this exoplanetary system.”

The detected water most likely came from a minor planet, at least 60 miles in diameter but probably much larger, that once orbited the GD 61 star before it became a white dwarf around 200 million years ago, the statement said.

Previous and current astronomical observations have measured the size and density of exoplanets, but not their composition, because conventional work was only done on planets orbiting living stars, Keck astronomers said.

But the only way to see what a distant planet is made of is to take it apart, say the researchers, and nature does this in a dying white dwarf system through its extreme gravitational pull – sucking in and shredding the surrounding material.

The resulting debris was analyzed using powerful spectrograph instruments installed on the Keck I and Keck II telescopes.

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