A large asteroid or comet smashed into Jupiter early Sunday, leaving a giant “;scar”; on the planet that was seen by scientists at NASA's Infrared Telescope Facility on Mauna Kea.

“;It's a fairly rare event,”; only the second time results of an impact on a planet were observed, said Alan Tokunaga, facility director with the University of Hawaii Institute for Astronomy.

The first one was 15 years ago when pieces of comet Shoemaker-Levy 9 collided with the planet, he said.

“;We knew that comet was going to hit Jupiter. This one was unexpected.”;

The new impact, which occurred at about 6 a.m. Hawaii time, was first reported by Anthony Wesley, an amateur astronomer in Australia. Wesley said on his Web site that he almost missed seeing it because he was tired after a late-night sky-watching session.

By 1 a.m. his time, he said he decided to observe another half-hour.

“;I noticed a dark spot rotating into view in Jupiter's south polar region and was starting to get curious. ... As it rotated further into view, and the conditions also improved, I suddenly realized it wasn't just dark; it was black in all channels, meaning it was truly a black spot.”;

Coincidentally, Glenn Orton, a researcher from the Jet Propulsion Laboratory in Pasadena, Calif., was scheduled to observe Jupiter at the Infrared Telescope Facility, said Tokunaga.

Orton “;was quite excited about the announcement (from Wesley),”; he said. “;It worked as well as if we planned it.”;

The likely impact point was shown in infrared images near the south polar region of the planet.

“;It turned out it's a very high-altitude feature,”; Tokunaga said.

He said some observatories are studying the spectra of the cloud feature. “;It might be possible to say something about whether it's an asteroid or comet just from the composition of clouds.”;

Hawaii astronomy graduate Paul Kalas, now at the University of California, Berkeley, saw a bruise on Jupiter about the size of the Pacific Ocean during scheduled viewing time in early morning hours Monday from the Keck II telescope on Mauna Kea.

He said he and his colleagues have a chance now to test theories developed after the Shoemaker-Levy 9 impact events.

Orton and his team have continued to track the planet and are trying to get more observing time on the NASA infrared telescope and others.

In a NASA news release Monday, the JPL scientist said: “;We were extremely lucky to be seeing Jupiter at exactly the right time, the right hour, the right side of Jupiter to witness the event. We couldn't have planned it better.

“;It's been a whirlwind of a day, and this on the anniversary of the Shoemaker-Levy 9 and Apollo anniversaries is amazing,”; he said.