Using the Hubble Space Telescope's Imaging Spectrograph, scientists have witnessed the most intense and fleeting flare ever seen in Jupiter's aurora. "The amount of energy released is comparable to an atomic bomb blast," Randy Gladstone of the Southwest Research Institute (SwRI) says. Gladstone and his colleagues from SwRI and the University of Michigan describe the event, shown at the right, in today's issue of Nature.

Image: SwRI

The flare, which occurred on September 21, 1999, at latitudes between 60 and 70 degrees, stretched several thousand kilometers across and reached a peak brightness of 37 megaRayleighs (MR). In short, the intensity of the emission increased by a factor of 30 in a matter of seconds and then waned as quickly.

The researchers are still unsure about what caused the disturbance. Auroral flares on Jupiterthe most powerful in the solar systemare often fueled by the planet's own rotation. But scientists suspect that pressure from the solar wind on Jupiter's magnetosphere may also contribute. Researchers are now analyzing and coordinating data that the Cassini, Hubble and Galileo spacecraft took of solar wind conditions and auroral activity around Jupiter in December 2000. "We expect the data from these observations to give us some insight into whether or not the solar wind plays a role in transient events like the one we saw," Gladstone says.