Watery asteroid in dying star points to habitable exoplanets

Artist impression of a rocky and water-rich asteroid being torn apart by the gravity of the white dwarf star GD 61.
Credit: Mark Garlick
Date:16 October 2013 Tags:, , ,

Astronomers have found the shattered remains of an asteroid that contained huge amounts of water orbiting an exhausted star, or white dwarf. This suggests that the star GD 61 and its planetary system – located about 150 light years away and at the end of its life – had the potential to contain Earth-like exoplanets, they say.

This is the first time that both water and a rocky surface – two “key ingredients” for habitable planets – have been found together beyond our solar system.

Earth is essentially a ‘dry’ planet, with only 0,02 per cent of its mass as surface water, so oceans came long after it had formed: most likely when water-rich asteroids in the solar system crashed into our planet.

The new discovery shows that 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 asteroid analysed is composed of 26% water mass, very similar to Ceres, the largest asteroid in the main belt of our solar system. Both are vastly more water-rich compared with Earth.

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.

They describe it as a “look into our future” as, six billion years from now, alien astronomers studying the rocky remains around our burned out Sun might reach the same conclusion – that terrestrial planets once circled our parent star.

The new research findings are reported in the journal Science.

All rocky planets form from the accumulation of asteroids, growing until full size, so asteroids are essentially the ‘building blocks’ of planets.

“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,” said lead author Jay Farihi, from Cambridge’s Institute of Astronomy.

“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 researchers say that the water detected most likely came from a minor planet, at least 90 km in diameter but probably much larger, that once orbited the GD 61 star before it became a white dwarf around 200 million years ago.

Source: University of Cambridge