Asteroid may hold secret to Earth's water
The Straits Times 1 May 2010
Discovery of water in dry asteroid likely to throw light on planet's past
The discovery could help explain where early Earth first got its water.
It also makes asteroids more attractive to explore, dovetailing with President Barack Obama's announcement that astronauts should visit an asteroid. And it even muddies the definition between comets and asteroids, potentially triggering a Pluto-like scientific spat over what to call these solar system bodies.
Two teams of scientists observed asteroid 24 Themis, one of the bigger rocks in the asteroid belt between Mars and Jupiter, with temperatures of around -73 deg C.
This asteroid has an extensive but thin frosty coating, and is likely replenished by a reservoir of frozen water deep inside rock once thought to be dry and desolate, scientists reported in two studies in yesterday's issue of the journal Nature.
One team led by Professor Humberto Campins of the
Astronomers have long theorised that hydrogen and oxygen and bits of water locked in clay are in asteroids, but this is the first solid evidence.
Furthermore, scientists found organic molecules, similar to what may have started life on Earth, Prof Campins said.
'This asteroid holds clues to our past and how the solar system and water on Earth may have originated and it also has clues to our future with exploration of near-Earth asteroids,' he said.
When it formed billions of years ago, Earth was dry, scientists say, and the water came from crashing comets that are essentially icy snowballs.
But comets have been found to carry more heavy hydrogen than the water in our oceans, said Mr Donald Yeomans, manager of the National Aeronautics and Space Administration's Near Earth Object Programme office. Icy asteroids between Mars and Jupiter might have the right heavy hydrogen ratio to match what is on Earth, said Mr Yeomans, who was not involved in the studies.
Normally, the ice on the asteroid should have escaped Themis as a gas over thousands of years, but it is still there, Prof Campins said. That means there is likely a supply of ice inside the rock, replenishing the surface, he said.
And if that is the case for other similar asteroids, then it would be a boon for visiting astronauts, who could use the water to drink and to help make fuel.
The icy asteroid also blurs differences between them and the comet. The general definition has been that asteroids are dry rocks and comets icy snowballs.
Now it seems to be more of a continuum of dry and icy with not much difference between the two, Prof Campins and others said.
And that, said Professor Andrew Rivkin of Johns Hopkins University, co-author of the other study in Nature, could wind up another controversy like the debate a few years ago about whether Pluto was a planet.
ASSOCIATED PRESS
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