On July 19, 2009 an Australian amateur astronomer, Anthony Wesley, observed a spot on the surface of Jupiter. The spot was created when a small object plunged into Jupiter's atmosphere and disintegrated. A similar phenomena was observed 15 years ago, but there is no other recorded history of such an event. Telescopes around the world have been focused on what is now a new, expanding spot on the planet's surface.
It looks like NASA got the Hubble up and running just in time. They were in the process of calibrating the telescope after recent lens upgrades and other refurbishments when the impact occurred and they interrupted the checkout to aim the telescope at the spot. A team of astronomers is now using the Hubble to study the event.
The spot was caused by the impact of a comet or an asteroid and is changing daily in the planet's clouds. According to Amy Simon-Miller of NASA, this magnitude of impact is rare. She estimated that the diameter of the object that slammed into Jupiter was at least the size of several football fields. The force of the explosion was thousands of times more powerful than the suspected comet or asteroid that exploded over the Tunguska River Valley in Siberia in June 1908. Details seen in the Hubble view show a lumpiness to the debris plume caused by turbulence in Jupiter's atmosphere. The spot is currently twice the length of the United States.