Astronomy Picture of the Day

Explanation: Unexpectedly, Comet LINEAR is breaking up. In retrospect, clues of its demise have been surfacing all month as the new comet has been approaching the Sun and brightening with dramatic flares. Above, the Hubble Space Telescope captured Comet C/1999 S4 LINEAR early this month blowing off a large piece of its crust. Recent speculation holds that the nucleus completely disrupted on or about July 24. If true, the elongated train of material should continue to ablate and orbit the Sun, but may now fade much more quickly. The break up of a bright comet is unusual but not unprecedented, as Comet Shoemaker-Levy 9 broke up before it struck Jupiter in 1994, and Comet Bennett broke apart as it neared the Sun in 1974. Future observations will tell if Comet LINEAR's first trip into the inner Solar System is its last.