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% 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.
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.
"Our results demonstrate that there was definitely potential for habitable planets in this exoplanetary system."
"This supports the idea 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."
"This supports the idea 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."
Artist's impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star GD 61. Similar objects in the solar system likely delivered the bulk of water on Earth and represent the building blocks of the terrestrial planets. Credit: © Mark A. Garlick, space-art.co.uk, University of Warwick and University of Cambridge
