Alerted by those observations, a team of astronomers from the University of Hawaii led by Yanga R. Fernández examined the comet with the university's 2.2-meter telescope atop Manua Kea. Their images revealed 18 additional fragments that ranged in brightness from magnitude 20 to 23.5. While the bulk of the comet's nucleus apparently remains intact, its castoffs have already spread across a half degree of sky, roughly 1,000,000 kilometers.
Evidence suggests that the breakup began six years ago when comet 57P last came its closest to the Sun. On its way out, the comet "flared," becoming five magnitudes brighter than expected. The debris field implies that sunlight induced thermal stresses in the nucleus and led to the fragmentation.
This is the third such breakup to be closely monitored. But unlike comet Shoemaker-Levy 9, whose fragments plunged into Jupiter in 1994, or comet LINEAR (C/1999 S4), which had pieces that exploded in light like fireworks before quickly fading to nothing, comet 57/P's pieces will disappear more slowly. The fragments' longevity will allow scientists to track their evolution and gain a better understanding of the structure and fragility of all comets.