New Jupiter Scar Bigger than the Pacific

Astronomers in the Bay Area and around the world are all agog over an immense scar larger than the Pacific Ocean that has suddenly appeared on the surface of Jupiter.

For only the second time in the 400 years since Galileo trained his primitive telescope on Jupiter, professionals and amateurs alike are observing how the planet has been blasted by a cosmic collision, and excitement is mounting about the mystery.

The only similar impact occurred 15 years ago, when chunks of Comet Shoemaker-Levy rained down on the planet at interplanetary speeds for five days and pitted the gaseous surface with clusters of huge black spots.

That crash has intrigued astronomers ever since, and they have been hard at work analyzing its effects on the planet in scientific paper after paper.

The new scar was first detected Sunday by Anthony Wesley, an amateur astronomer in Australia, who promptly posted on a blog for other astronomers.

Franck Marchis of the SETI Institute in Mountain View soon posted on his own blog about a huge black spot detected near Jupiter's south pole. He followed it with more blog posts about its nature after colleagues using the powerful Keck telescope in Hawaii saw it as "an anomalous bright spot" shining in the infrared region of the spectrum.

If the object that hit Jupiter was an asteroid rather than a comet, it might well have been one of those millions of objects that normally fly around the sun in the "asteroid belt" between Mars and Jupiter. But so far, no one knows.

"We really have no idea what it was, and our observations so far have only confirmed that the scar did indeed come from an impact," Marchis said in a phone interview Tuesday. "If more observations in the infrared show water in the scar, then the impactor was most probably a comet, as comets do hold water; but if not, then it was most probably an asteroid."

After Marchis alerted many colleagues Sunday night, astronomers Mike Wong from UC Berkeley and Michael Fitzgerald of UCLA and the Lawrence Livermore National Laboratory used the Keck telescope to make detailed observations of the impact site.

"Whatever hit Jupiter this time," Marchis wrote on his blog, "it was not disrupted with multiple fragments like Shoemaker-Levy."

Wong said the scar covers 73 million square miles in an irregular shape. By comparison, most geographic maps set the Pacific Ocean's size as about 60 million to 69 million square miles.

The scar's complex, blotchy shape indicates that the mysterious object must have exploded into fragments before it hit Jupiter, Marchis said, and was probably too small to be detected by any Earth-bound telescopes aimed at the planet before the crash.

Marchis hoped to make new observations of the scar Tuesday night from the Lick Observatory atop Mount Hamilton above San Jose. Other professional and amateur astronomers are also training telescopes on Jupiter's clouded surface, trying to analyze the scar and determine what caused it.