Jupiter’s Mysterious June 3rd Collision -Why Was There No Visible Impact Cloud?

Hs-2009-23-a-web_print_strip On June 3rd, 2010, a massive comet or asteroid struck Jupiter's cloudtops, and disintegrated, producing a flash of light so bright it was visible in backyard telescopes on Earth. Observers around the world aimed their optics at the impact site, waiting to monitor the cloud of ash debris which seemingly always accompanies an impact of this size (like that shown left from last July 2009 Pacific-sized impact).

"It's as if Jupiter just swallowed the thing whole," says Anthony Wesley, 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."  The color composite image left is of the June 3rd Jupiter impact flash. captured by Wesley of Broken Hill, Australia.

"We've seen things hit Jupiter before," says planetary scientist Glenn Orton of JPL, "and the flash of impact has always been followed by some kind of debris."

When fragments of Comet Shoemaker-Levy 9 hit Jupiter in 1994, for examples, 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. Last summer, in July 2009, Wesley discovered a similar mark the size of the Pacific Ocean thought to be debris from a rogue asteroid crashing into the planet.

A possibility about the missing debris cloud 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."

In an odd coincidence, the object struck right in the middle of Jupiter's South Equatorial Belt (SEB), one of the two broad stripes that girdle the planet. This is "curious" because the SEB itself vanished earlier this year. Orton has proposed that the missing belt still exists, it's just temporarily hidden underneath some high-altitude cirrus clouds, which just might also be cloaking the impact debris.

We may never know.

One thing is sure: "Jupiter is getting hit more than we expected," says Don Yeomans, head of NASA's Near-Earth Object program of JPL. "Back in the days of Shoemaker-Levy 9 (SL-9), we calculated that we should see an impact on Jupiter once every hundred years or so. We considered ourselves extraordinarily lucky to witness the SL-9 event."

"But look where we are now," he continues. "Anthony Wesley has observed two impacts within the past 12 months alone. It's time to revise our impact models [particularly for small impactors]."

Clearly, researchers have a lot to learn, not only about how often Jupiter gets hit, but also what happens when the strikes occur.

"We're continuing the search for debris at a number of major observatories, including Hubble," says Orton. According to NASA experts, future observations sensitive to very small amounts of debris and to gases pulled up from Jupiter's deeper atmosphere may yet reveal what happened to the flashy impactor of June 3rd—or lead researchers in new directions entirely.

Casey Kazan via Science@NASA

Image below shows clouds of debris marking Jupiter's cloudtops following the SL-9 impacts of 1994.

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