What Hit Jupiter in 2009?

The body that slammed into Jupiter last July almost certainly was an asteroid rather than a comet, and such impacts might happen as often as every 10 to 15 years, new calculations and an analysis of observations taken last summer suggest.

If researchers are correct in their analysis, images taken by the Hubble Space Telescope and other instruments may have captured for the first time the immediate aftermath of an asteroid striking a planet.

The circumstantial evidence in favor of an asteroid comes in part from comparing Hubble Space Telescope images of the 2009 impact site with Hubble images of Jupiter recorded in 1994, when another impactor, the comet Shoemaker-Levy 9, struck the planet.…