A color composite image of the June 3rd Jupiter impact flash.
Credit: Anthony Wesley of Broken Hill, Australia
On June 3rd, 2010, something hit Jupiter. A comet or asteroid descended from the black of space, struck the planet's cloudtops, and disintegrated, producing a flash of light so bright it was visible in backyard telescopes on Earth.
Soon, observers around the world were training their optics on the impact site, waiting to monitor the cindery cloud of debris which always seems to accompany a strike of this kind. They're still waiting.
"It's as if Jupiter just swallowed the thing whole," says Anthony Wesley of Australia, one of two amateur astronomers who recorded the initial flash.
The other, Christopher Go of the Philippines, says "it was thrilling to see the impact, but the absence of any visible debris has got us scratching our heads."
Indeed, it is a bit of a puzzle. "We've seen things hit Jupiter before," says planetary scientist Glenn Orton of NASA's Jet Propulsion Laboratory in California, "and the flash of impact has always been followed by some kind of debris."
For instance, when fragments of Comet Shoemaker-Levy 9 hit Jupiter in 1994, each major flash observed by NASA's Galileo spacecraft produced a "bruise," a murky mixture of incinerated comet dust and chemically altered Jovian gas twisting and swirling among the native clouds.
Just last year, in July 2009, Wesley discovered a similar mark thought to be debris from a rogue asteroid crashing into the planet. So where is the debris this time?
A possibility offered by some observers is that the flash wasn't an impact at all. Maybe Go and Wesley witnessed a giant Jovian lightning bolt.
"I consider that very, very unlikely," says Orton. "NASA spacecraft have seen lightning on Jupiter many times before, but only on the planet's nightside. This dayside event would have to be unimaginably more powerful than any previous bolt we've seen. Even Jupiter doesn't produce lightning that big."
Nor could it be a flash of lightning in Earth's atmosphere fortuitously happening in front of Jupiter. Simultaneous observations of the same flash from widely spaced observatories in Australia and the Philippines rule that out. For the same reason, it couldn't be, say, a terrestrial meteor or any other phenomenon in the atmosphere of Earth.
