Washington: A large near-Earth object that was believed to be an asteroid has now been classified as a comet.
Called 3552 Don Quixote, the body is the third largest near-Earth object-mostly rocky bodies, or asteroids, that orbit the Sun in the vicinity of Earth. About 5 percent of near-Earth objects are thought to be "dead" comets that have shed all the water and carbon dioxide in the form of ice that give them their coma - a cloud surrounding the comet nucleus - and tail.
The discovery could hold implications for the origin of water on Earth.
Joshua Emery, assistant professor of Earth and planetary sciences at the University of Tennessee, Knoxville, said that Don Quixote`s orbit brings it close to Earth, but also takes it way out past Jupiter.
He said that such a vast orbit is similar to a comet`s, not an asteroid`s, which tend to be more circular - so people thought it was one that had shed all its ice deposits.
Using the Spitzer Space Telescope operated by the Jet Propulsion Laboratory at the California Institute of Technology under contract with NASA, the team-led by Michael Mommert of Northern Arizona University-reexamined images of Don Quixote from 2009 when it was in the part of its orbit closest to the Sun, and found it had a coma and a faint tail.
Emery also reexamined images from 2004, when it was at its farthest distance from the Sun, and determined that the surface is composed of silicate dust, which is similar to comet dust.
He also determined that Don Quixote did not have a coma or tail at this distance, which is common for comets because they need the Sun`s radiation to form the coma and the Sun`s charged particles to form the tail.
This discovery may have implications for the origins of water on Earth as comets may be the source of at least some of it, and the amount on Don Quixote represents about 100 billion tons of water .