小行星或成为研究地球物种起源的“活化石”

The first-ever discovery of ice and organic molecules（分子，微粒） on an asteroid（小行星） may hold clues to the origins of Earth's oceans and life 4 billion years ago. University of Central Florida researchers detected a thin layer of water ice and organic molecules on the surface of 24 Themis（西弥斯女神） , the largest in a family of asteroids orbiting between Mars and Jupiter.

Their unexpected findings will be published Thursday, April 29 in Nature, which will feature two complementary（补充的） articles by the UCF-led team and by another team of planetary（行星的） scientists.

"What we've found suggests that an asteroid like this one may have hit Earth and brought our planet its water," said UCF Physics Professor Humberto Campins, the study's lead author.

Some theories suggest asteroids brought water to Earth after the planet formed dry. Scientists say the salts and water that have been found in some meteorites（陨星，陨石） support this view.

Using NASA's Infrared Telescope Facility in Hawaii, Campins and his team of researchers measured the intensity of the reflected sunlight as 24 Themis rotated. Differences in intensity at different wavelengths helped researchers determine the makeup（组成，化妆品） of the asteroid's surface.

Researchers were surprised to find ice and carbon-based compounds evenly distributed（分布的，分散的） on 24 Themis. More specifically, the discovery of ice is unexpected because surface ice should be short lived on asteroids, which are expected to be too warm for ice to survive for long.

The distance between this asteroid and the sun is about three times greater than between Earth and the sun.

Researchers will continue testing various hypotheses（假定，臆测） to explain the presence of ice. Perhaps most promising is the possibility that 24 Themis might have preserved the ice in its subsoil（底土） , just below the surface, as a kind of "living fossil" or remnant（剩余） of an early solar system that was generally considered to have disappeared long ago.