Credit: NASA/Swift/DSS/D. Bodewits (UMD) On December 11, 2010,
an otherwise nondescript asteroid named Scheila brightened
suddenly. In addition, the asteroid showed evidence of plume-
like jets of gas emanating from its surface. It was almost as if
this asteroid was transforming itself into a comet. Comets and
asteroids are two separate categories of objects, of course:
comets are huge interplanetary snowballs, while asteroids are
giant rocks hurtling through space. But we know now that some
asteroids apparently have substantial pockets of ice and other
volatile materials below the surface, and in rare instances this
material can become exposed and blow off the surface when heated
by the sun. To see if this was happening, astronomers trained
the Ultraviolet and Optical Telescope (UVOT) aboard the Swift
spacecraft observatory at Scheila, and, a few days later, the
cameras on the Hubble Space Telescope. The UVOT image of Scheila
is shown above. The image of the comet was overexposed to reveal
faint dust plumes i