London, October 13 (ANI): Two independent scientific teams have found what may be the first direct evidence of water ice on the surface of an asteroid, a discovery that lends support to the idea that asteroids could have helped deliver water to the early Earth.
Asteroids are generally considered to be rocky, and comets icy. That's because ice in the early solar system is thought to have formed beyond a "snow line" lying somewhere between Mars and Jupiter.
Asteroids forming beyond that boundary could contain ice.
But, it is not clear how common ice might be in the main asteroid belt, because sunlight is expected to quickly vaporise ice on the surfaces of airless bodies that fly closer to the sun than Jupiter.
In 2008, however, Andrew Rivkin of Johns Hopkins University in Laurel, Maryland, and Joshua Emery of the SETI Institute in Mountain View, California, found hints that the asteroid 24 Themis, which sits in the main asteroid belt between Mars and Jupiter, could have water ice on its surface.
The team found the water signal by measuring the spectrum of infrared light radiated by the object.
Now, according to a report in New Scientist, a second team has found the water ice signature using the same telescope, NASA's Infrared Telescope Facility in Hawaii.
The new observations suggest water ice, mixed with organic molecules, is "widespread on the surface of the asteroid," said Humberto Campins of the University of Central Florida in Orlando.
That is surprising, since the asteroid's distance from the sun means it should lose about 1 metre of ice each year.
"This ice is unstable, and therefore we need a process to explain why there is ice on the surface now," said Campins.
One possibility is that an icy object might have collided with 24 Themis, leaving behind a layer of ice.
Alternatively, the ice could have been part of the asteroid's parent body, which is thought to have broken up about 2.5 billion years ago, producing a family of asteroids with orbits similar to that of 24 Themis.
"What is most likely the case is that the parent body (of this family) was water-ice-rich, was broken up, and now the surface of its largest fragment, Themis, has been impact-excavated, revealing the ice that was once deep in a larger object," said Britney Schmidt of UCLA.
"It is exciting to finally get a glimpse inside a water-rich body," she added. (ANI)