Asteroid ice may have played role in seas


POSTED: Sunday, May 02, 2010

The discovery of ice on a large asteroid between Mars and Jupiter shatters the typical picture of these bodies as mostly rocks and metals. It also supports the hypothesis that water from asteroids helped create Earth's oceans.

“;In a way, it's a new kind of asteroid,”; Hawaii astronomer Alan Tokunaga said in an interview. He is chief of the NASA Infrared Telescope Facility operated on Mauna Kea by the University of Hawaii Institute for Astronomy.

In studies with the telescope, two teams of scientists said they found frozen water on 24 Themis, a relative monster asteroid some 100 miles wide. For comparison, that's about the length of the Big Island. Their findings were reported Thursday in the journal Nature.

“;Another surprise of this is, perhaps asteroids contain more water than we suspected and also were a major contributor to water on Earth,”; Tokunaga said.

Just as intriguing, the scientists found evidence of organic material, he said, which raises speculation that “;asteroids like this could have delivered a lot of organic material to Earth as well when the Earth was forming.”; That material could have provided the building blocks for life here, scientists say.

Said Tokunaga, “;The Earth probably was built up by small bodies of asteroids and comets, but we don't know what fraction of water on Earth came from comets and what came from asteroids. We always thought comets were the main source.”;

Bobby Bus, UH support astronomer at the NASA facility, said scientists have seen evidence of water on asteroids before, but in “;hydrated form”;—minerals altered by water.

What wasn't seen until now was direct evidence for water frost on an asteroid “;like you would find in your freezer,”; he said. “;What makes this interesting is at the distance that this asteroid is from the sun, one would not expect water frost to be able to exist very long ... so that means there has to be a source, some process going on, which is replenishing that frost.”;

That points to ice below the surface.

The scientists are looking at other members of the 24 Themis family, products of an ancient collision, to see if they have the same water feature, Bus said.

NASA plans to send astronauts to a nearby asteroid in about 15 years as a stepping stone to Mars.

If smaller asteroids, especially those closer to Earth, are similar to Themis and store interior ice, it would be a boon for astronauts, who could drink the water and use it to make fuel.