Ice among the rocks
By Ron Cowen
Researchers have found a trio of icy comets hidden among the thousands of rocks in the main asteroid belt between the orbits of Mars and Jupiter. Such comets, which don’t fit into any known class, could have been primary sources of water that transformed the early, dry Earth.
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Each member of the trio, dubbed main-belt comets by codiscoverers Henry Hsieh and David Jewitt of the University of Hawaii in Honolulu, appears to have formed inside Jupiter’s orbit. That’s in contrast to most other comets, which were born beyond Neptune in the chilliest parts of the solar systems.