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The Sciences

Followup: Jupiter impact video, and a color picture!

Bad AstronomyBy Phil PlaitJune 4, 2010 6:31 PM


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Anthony Wesley, who discovered the impact event on Jupiter yesterday, has posted a lovely color image of the flash:


Wow. He was only taking greyscale video, but put together a three-color composite and added in the data from the flash. So this image is not precisely real, but on the other hand is no less real than other astronomical images. He has also posted a greyscale video of the flash which is pretty tremendous, too. It's also up on YouTube: Note the ring of light just around the flash itself, just barely visible around the central point. That's probably not a physical halo; it's an artifact of how telescopes and detectors see bright point sources -- the way the light spreads out in an optical system is called the point spread function. Many Hubble images of stars, for example, show the same ring. By coincidence, the impact point appears to be near the edge of where the South Equatorial Belt on Jupiter is. That's the belt that disappeared recently. That's guaranteed to be a coincidence; the belt vanished many weeks ago. And I expect some folks will ask if the impact may affect the belt. My gut says no. You have to appreciate the scale of what you're seeing here: Jupiter is 140,000 km (86,000 miles) across -- 11 times the diameter of the Earth! In this picture, the Earth wouldn't even stretch across the North Equatorial Belt, the dark red band above Jupiter's equator. So even though this explosion may have been the equivalent of thousands of nuclear weapons all blowing up at once, it probably will only have a passing and unnoticeable effect on Jupiter's weather. But note: I'm guessing. Jupiter is a complex and weird planet. Also, a lot of people are asking how this can be an impact if Jupiter isn't solid. After all, what's getting hit? Again, remember the scale. What you're seeing on Jupiter is the tops of its clouds, which are tens of thousands of kilometers deep. When a large rock enters at high speed -- and with Jupiter's gravity, those speeds can reach 80 km/sec (50 miles/sec) or more -- it slams into the air and feels a huge amount of pressure. Moving at hypersonic speeds, it compresses the gas violently, and the gas heats up. The rocks slows, converting its enormous energy of motion into heat. It also starts to break up due to stress, creating many smaller chunks. These each slam the gas and heat it, and also get stressed. They fall apart, creating smaller chunks... and at some moment, usually just seconds after everything starts, the pieces are so small they burn up completely due to the heat, dumping all their energy all at once into the atmosphere. This happens so suddenly, and the energy release so vast, it's by any definition an explosion. The bigger the rock, and the faster it moves, the more explosive energy it releases. A rock 1 kilometer (0.6 miles) across moving at 80 km/sec will explode with the energy of almost <Dr. Evil>one million one-megaton bombs</Dr. Evil>. So that's why you don't need to hit anything solid to make a big boom. By the way, had this event happened here on Earth with the same energy release, it wouldn't be an extinction level event like the dinosaur killer, but it would -- not to get too technical or anything -- suck mightily. Anything within hundreds of kilometers would be totaled and burning, global weather patterns would be affected, and even though it wouldn't kill everybody, I expect there would be a global economic collapse that would cripple the planet. And I wonder if some governments might see this as an opportune time to attack any pesky neighbors... happily, on average an impact this large is extremely rare, like once every half million years or so. It's not clear how often Jupiter gets hit, and this is only the third confirmed impact we've seen (along with the Shoemaker Levy 9 comet impact in 1994, and last year's asteroid impact also discovered by Wesley). But with amateurs getting more sophisticated in their technique and equipment, expect to see more of these. And they can monitor Jupiter far better and more completely than professional observatories can (which are usually pointed elsewhere; it's a big sky), so not only will we see more of these, but they'll be almost exclusively the domain of the amateur astronomer. And my sincere and very hearty congratulations and thanks to Wesley and Christopher Go for their amazing images and footage of this incredible event!

Image and video credit: Anthony Wesley

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