NASA's Spitzer Space Telescope captured this image of comet Holmes in March 2008, five months after the comet suddenly erupted and brightened a millionfold overnight.

Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes mysteriously exploded as it approached the asteroid belt.