Astronomers were scrambling to get big telescopes turned to Jupiter on Tuesday to observe the remains of what looks like the biggest smashup in the solar system since fragments of the Comet Shoemaker-Levy 9 crashed into the planet 15 years ago.
Something — probably a small comet — smacked into Jupiter on Sunday, leaving a bruise the size of the Pacific Ocean near its south pole. Just after midnight, Australian time, Jupiter came into view in the eyepiece of Anthony Wesley, an amateur astronomer in Murrumbateman, Australia. The planet was bearing a black eye spookily similar to the ones left in 1994.
"This was a big event," said Leigh Fletcher of the Jet Propulsion Laboratory, a NASA lab technician in Pasadena, Calif. "In the inner solar system it would have been a disaster."
Wesley, a 44-year-old computer programmer from the village north of Canberra, made the discovery "using his backyard 14.5-inch reflecting telescope," according to the Sydney Morning Herald. (For the record, 14.5 inches is the diameter of the telescope's mirror inside. His "back yard" telescope is taller than he is.) The paper explained: "Wesley, who has been keen on astronomy since he was a child, said telescopes and other astronomy equipment were so inexpensive now that the hobby had become a viable pastime for just about anybody. His own equipment cost about $10,000."
Glenn Orton, a scientist at the Jet Propulsion Laboratory, said, "It could be the impact of a comet, but we don't know for sure yet."
Astronomers admit they might never know for sure. "It's like throwing a stone on the pond," Fletcher said. "You see the splash, but lose the stone. It's the splash we can study."
Fletcher said that he and his colleagues were frantically writing proposals for telescope time. Among the telescopes they have recruited is the Hubble Space Telescope, making its early return to the fray after a successful repair mission by astronauts this summer.
The discovery began as a routine night-gazing exercise. Wesley pointed his new telescope to the cosmos and started snapping images.
Conditions weren't ideal and when the sky got murkier, Wesley almost quit.
Instead, he took a half-hour break to watch sports on TV. When he peered back into the telescope, he noticed a curious black spot on Jupiter.
Was it a moon or a shadow? Can't be, he thought.
Wesley checked images that he took just two days earlier and found no sign of the spot.
Was Jupiter struck by something?
"I had no real idea, and the odds on that happening were so small as to be laughable, but I was really struggling to see any other possibility given the location of the mark," he wrote in an online posting. "If it really was an impact mark, then I had to start telling people, and quickly."
Wesley fired off an e-mail to a group of amateur and professional astronomers, among them Fletcher and Orton, who was preparing to look at Jupiter using NASA's infrared telescope on Mauna Kea, Hawaii. He confirmed Wesley's finding.
Images released by NASA show the impact occurred near the south pole and caused debris to fly into the upper atmosphere. The scar is pale-looking from the reflection of debris.
Jupiter is 1,400 times larger than Earth. At its closest, Jupiter is about 390 million miles from Earth, four times as far as the Earth is from the sun.
Franck Marchis, an astronomer at the SETI Institute and the University of California at Berkeley, said the shape of the debris splash as revealed in Keck II telescope images suggested that whatever hit Jupiter might have been pulled apart by tidal forces from the planet's huge gravity before it hit. In an e-mail message, he said humans should be thankful for Jupiter.
"The solar system would have been a very dangerous place if we did not have Jupiter," he wrote. "We should thank our giant planet for suffering for us. Its strong gravitational field is acting like a shield protecting us from comets coming from the outer part of the solar system."
Information from the New York Times, Associated Press and Los Angeles Times was used in this report.