Jupiter's New Bruise Big As Pacific Ocean
The scar from the probably impact appeared July 19 in Jupiter's southern hemisphere, and has grown to a size greater than the extent of the Pacific Ocean. This infrared image taken with Keck II on July 20 shows the new feature observed on Jupiter and its relative size compared to Earth.
Credit: Paul Kalas (UCB), Michael Fitzgerald (LLNL/UCB), Franck Marchis (SETI Institute/UCB), James Graham (UCB)

The dark bruise that appeared suddenly near the south pole of Jupiter several days ago, likely as the result of an impact by a comet or asteroid, is as big as the Pacific Ocean, astronomers report.

The dark spot was first noticed by chance by amateur astronomer Anthony Wesley in Australia on Sunday, July 19.

The blemish is thought to be the result of an impact similar to that of Comet Shoemaker-Levy 9, which pummeled the gas giant 15 years ago.

After he was convinced the spot was not just another storm or the shadow of one of Jupiter's moons, Wesley alerted other astronomers around the world to the scar's appearance.

University of California, Berkeley, astronomer Paul Kalas took advantage of previously scheduled observing time on the Keck II telescope in Hawaii to image the blemish in the early morning hours of Monday, July 20. The near-infrared image showed a bright spot in the clouds of Jupiter's southern hemisphere, where the impact had propelled reflective particles high into the relatively clear stratosphere.

In visible light, the bruise appears dark against the bright surface of Jupiter.

These observations mark only the second time that astronomers have been able to see the results of an impact on the planet, the first being Comet Shoemaker-Levy 9's collision. Many theories were formed after that collision.

"Now we have a chance to test these ideas on a brand new impact event," Kalas, said.

Kalas and his colleagues hope their observations will shed light on the nature of the impact.

"The analysis of the shape and brightness of the feature will help in determining the energy and the origin of the impactor," said Marchis. "We don't see other bright features along the same latitude, so this was most likely the result of a single asteroid, not a chain of fragments like for SL9 [Comet Shoemaker-Levy 9]."

Mike Wong, a UC Berkeley researcher currently on leave at the Space Telescope Science Institute in Baltimore, used the observations to calculate that the bruise is near the southern pole of Jupiter (305 degrees west longitude and 57 degrees south latitude in planetographic coordinates) and that the impact covers a 190-million-square-kilometer area, as big as the Pacific Ocean.

Because of the complex shape of the explosion, it is possible that tidal effects (the gravitational tugs of Jupiter and its moons) fragmented the impactor ? a comet or asteroid ? shortly before it collided with the planet.

Later this week, astronomers from UC Berkeley and around the world plan to conduct high-resolution visible and ultraviolet observations of the impact site using the Hubble Space Telescope's brand new Wide Field Camera 3. Ground-based facilities including the W. M. Keck telescope will also use adaptive optics to obtain much sharper infrared images of the impact's aftermath.