spacetoday.net: New type of comets may be source of Earth's water

Posted: Fri, Mar 24, 2006, 8:14 AM ET (1314 GMT)
Main belt comet images (UH/IfA)

A new class of comets discovered in the main asteroid belt could be the source of the Earth's water, astronomers said Thursday. In a paper published Thursday by Science Express, the online arm of the journal Science, astronomers at the University of Hawaii reported the discovery of three "main-belt comets", objects located in the main belt of asteroids. The objects have asteroid-like orbits but appear more like comets. The objects are thought to have formed inside the orbit of Jupiter rather than beyond the orbit of Neptune, where most other comets formed. Chemical analyses have shown that water ice in comets is different from water in the Earth's oceans, but scientists suggest that since the main-belt comets formed differently, their water ice may be more like the Earth's water and thus could have been the source for the Earth's water early in the history of the solar system.