Posted on 03/24/2006 2:26:05 AM PST by S0122017
Clandestine comets found in main asteroid belt 19:00 23 March 2006 NewScientist.com news service Kimm Groshong
You do not have to look to the outer edges of the solar system, or even out beyond Neptune to observe a reservoir of comets. A bevy of the ice-containing bodies lies disguised as main-belt asteroids between Mars and Jupiter, claim astronomers from the University of Hawaii, US.
David Jewitt and Henry Hsieh have dubbed the new population "main belt comets". They describe three objects with near circular, flat orbits in the asteroid belt that stream volatile materials, producing an observable tail for weeks and months at a time.
The finding backs a theory that ice-bearing asteroids – or "comets" – from this much closer region may have played an important role in forming the Earth's oceans.
Scientists once believed the icy comets from the outer regions of the solar system were the most likely source of the water that transformed the early Earth from a dry, barren world. But chemical analyses of comet water – carried out from a distance – ruled out the possibility.
Another possibility was asteroids. But it had seemed impossible to study the water content of asteroids since most of their water appears to have dissipated or is now buried too deeply to observe.
Window to the past Now Jewitt says this new population within the asteroid belt may provide a way to sample the chemicals in water on or near the surface of these objects. And he says the main-belt comets hold promise for future study as components of the protoplanetary disc that surrounded the Sun – the disc from which the planets formed. "They're a window to some early epoch, back when objects were accreting," he says.
The new study underscores the increasingly hazy distinction between comets and asteroids. "There are different definitions of comet used by different people at different times," Jewitt told New Scientist.
The two traditionally recognised comet reservoirs are the Kuiper Belt, a frigid region beyond Neptune's orbit, and the even more distant Oort Cloud. One definition describes a comet as an object following a highly elliptical, often inclined orbit with origins in one of these two reservoirs.
Carbonaceous covering But another definition involves what an observer sees either with the naked eye or through a telescope – a comet’s streaming gassy tail as it loses ice and other volatile materials through being warmed by the Sun.
Jewitt says based on their nearly circular, stable orbits, the main belt comets are "completely asteroidal". You would never guess that they were anything but asteroids." But in terms of appearance, with their long-lasting tails, he says "they're definitely comets".
The team believes in order to survive at such proximity to the Sun, the volatiles in the main belt comets would have to be covered by a layer of possibly carbonaceous material. They say an impact event could then uncover some of the volatiles, allowing the Sun's heat to trigger the observed outgassing.
Activated asteroids Asteroid expert Richard Binzel at MIT questions the need for the new classification. "I prefer to think of them as activated asteroids," he told New Scientist. "It's no surprise if some asteroids have some water content, particularly in the outer asteroid belt."
He says volatiles have been measured to make up about 10% of some carbonaceous meteorites that are thought to come from the region.
Jewitt says potentially tens of thousands of main belt objects contain ice and have simply not been observed during their active period. In order to be seen spewing dust, the objects would have to have been hit by a meteor size boulder within the last thousand years or so, he adds.
Journal reference: Science (DOI: 10.1126/science.1125150)
asteroids turn out to be comets & may support hypthesis around earth oceans ping
There're like assholes, only worry when they show up.
Democrats turn out to be aliens & may support hypothesis around flat earth ping
Sorry, had to do it.
Thats ok it was funny. Btw if you ever such a posting plz ping me :)
Thanks for the ping and topic!
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