Icy asteroid could finally reveal where Earth's water came from

Water ice and organic material has been discovered on the surface of an asteroid for the first time.
The discovery lends support to the theory that meteorites falling on Earth may have provided the kick-start to life.
Scientists found evidence of a thin film of ice covering 24 Themis, one of the hundreds of space rocks in the asteroid belt between Mars and Jupiter. The 125mile-wide object is one of the largest Main Belt asteroids.

24 Themis is one of the largest asteroids that orbits between Mars and Jupiter. Scientists have discovered evidence of water ice and organic material on the asteroid's surface.

Astronomers used Nasa's Infrared Telescope Facility in Hawaii to analyse sunlight reflected off the rock. They discovered signals consistent with frozen water, as well as organic material.
Josh Emery, from the University of Tennessee in Knoxville, said: 'The organics we detected appear to be complex, long-chained molecules. Raining down on a barren Earth in meteorites, these could have given a big kick-start to the development of life.'

Finding ice on the surface of the asteroid was a surprise because it would have been expected to evaporate quickly.
'This implies that ice is quite abundant in the interior of 24 Themis and perhaps many other asteroids,' Dr Emery added.
'This ice on asteroids may be the answer to the puzzle of where Earth's water came from.'
The research, reported in the journal Nature, suggests that the ice on 24 Themis is regularly being replenished.
This could occur as a result of water vapour released by buried ice 'outgassing' through cracks in the rock. Occasional collisions with space debris may also cause internal water to escape.
Themis belongs to an asteroid 'family' formed long ago from the fragmentation of a larger body. It is likely that the parent body also contained water ice, raising questions about how the Solar System was formed.

Water may be far more abundant in the asteroid belt than was previously thought, the scientists believe.
'Asteroids have generally been viewed as being very dry,' said Dr Emery.
'It now appears that when the asteroids and planets were first forming in the very early Solar System, ice extended far into the Main Belt region.
'Extending this refined view to planetary systems around other stars, the building blocks of life - water and organics - may be more common near each star's habitable zone.
'The coming years will be truly exciting as astronomers search to discover whether these building blocks of life have worked their magic there as well.'
The discovery blurs the dividing line between asteroids and comets.
Asteroids have long been thought of as rocky and comets icy. Once it was believed that comets brought water to the Earth and filled the oceans.
However, doubt was cast on this theory when it was found that comet water is atomically different to Earth water.
A second team of scientists led by Humberto Campins, from the University of Central Florida in Orlando, came to similar conclusions based on the appearance of light reflected from 24 Themis as it rotates. Dr Campins' findings are also reported in Nature.