Something slammed into Jupiter in the last few days, creating a dark bruise about the size of the Pacific Ocean. The bruise was noticed by an amateur astronomer on Sunday, July 19. 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 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.

The observation made with the Keck II telescope marks only the second time astronomers have seen the results of an impact on the planet. The first collision occurred exactly 15 years ago, between July 16 and 22, 1994, when more than 20 fragments of comet Shoemaker-Levy 9 collided with Jupiter.

The Shoemaker-Levy 9 (SL9) impact events were well-studied by astronomers, including several from UC Berkeley, and many theories were subsequently developed based on the observations.

"Now we have a chance to test these ideas on a brand new impact event," said Kalas, who observed the aftermath of the new impact with the help of Michael Fitzgerald of Lawrence Livermore National Lab and UCLA.

The astronomers decided to observe Jupiter after hearing that Australian amateur astronomer Anthony Wesley had discovered the planet's new scar. They read about it on the blog of UC Berkeley and SETI Institute astronomer Franck Marchis (http://www.cosmicdiary.org/blogs/nasa/franck_marchis/).

Kalas, who is in Greece, consulted intensely with Fitzgerald and Marchis on how best to observe the feature. Fitzgerald then performed the observations with the help of Keck Observatory astronomer Al Conrad.

"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."

"The fact that (the feature) shows up so clearly means that it's associated with high-altitude aerosols, as seen in the Shoemaker-Levy impacts," said James Graham of UC Berkeley, who assisted with the new observations as well as with observations taken during the SL9 event in 1994.

Mike Wong, a UC Berkeley researcher currently on leave at the Space Telescope Science Institute in Baltimore, used the observations to calculate that the scar is near the southern pole of Jupiter (305 W, 57 S 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 fragmented the impactor - a comet or asteroid - shortly before it collided with the planet.

The impact fell on the 15th anniversary of the SL9 impacts, but the coincidences do not end there. Kalas' original plan was to search for a previously detected, Jupiter-like planet around the star Fomalhaut. The star is located roughly 25 light years from Earth in the direction of the constellation Piscis Austrinus.

Kalas showed previously that the planet, dubbed Fomalhaut b, is bright, and one explanation for that brightness is that it is suffering impacts just like Jupiter, he said.

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.

But the Keck images reported here will provide a crucial baseline for measuring the spread of impact-related material, Wong said. No other method exists to directly track the winds at these rarified levels of Jupiter's atmosphere.

One of those planning to observe Jupiter with Keck is UC Berkeley astronomer Imke de Pater, who was one of the leaders of the campus's SL9 observations of Jupiter in 1994. Working with Conrad and Wong, she plans to observe Jupiter on July 24 using a laser guide star with adaptive optics, analogous to observations conducted in July 2006 and May 2008.