Recently Amateur astronomer Anthony Wesley was photographing Jupiter from his backyard observatory in Murrumbateman, Australia, when something odd caught his eye.
At first he thought it was another dark storm, but soon after he learnt that it was an impact mark. Something hit the giant planet!
"I had seen the scars caused by fragments of Comet Shoemaker-Levy 9 hitting Jupiter in 1994, so I knew what an impact looked like," he says. "After I'd convinced myself that this was real, I could hardly use the computer. My hands were shaking. It was quite unbelievable."
"We believe it was a comet or asteroid measuring perhaps a few hundred meters wide," says Don Yeomans of NASA's Near-Earth Object Office at JPL. "If something of similar size hit Earth—we're talking about 2000 megatons of energy--there would be serious regional devastation or a tsunami if it hit the ocean."
In a stroke of luck almost as big as Wesley's, JPL astronomers Glenn Orton and Leigh Fletcher were already scheduled to observe Jupiter on July 20th, barely a day after impact, using NASA's Infra-red Telescope Facility (IRTF) atop Mauna Kea in Hawaii. The 3-meter telescope revealed a fresh cloud of debris about the size of Mars floating among Jupiter's clouds.
The object is believed to have exploded in Jupiter's upper atmosphere and blew itself to smithereens. What they were able to see were the bits and pieces of the impactor and possibly some strange aerosols formed by shock-chemistry during the impact.
The cloud's chemical composition holds clues to the nature of the impactor. Orton says ground-based observers are now analyzing light reflected from the cloud to figure out what it is made of. "If the spectra contain signs of water, that would suggest an icy comet. Otherwise, it's probably a rocky or metallic asteroid."
Meanwhile, it's a big dark mystery—the kind that Wesley can't take his eyes off of.
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