Something has smashed into Jupiter, leaving behind a black spot in the planet's atmosphere, scientists confirmed on Monday.
This is only the second time such an impact has been observed. The first was almost exactly 15 years ago, when more than 20 fragments of comet Shoemaker-Levy 9 collided with the gas giant.
"This has all the hallmarks of an impact event, very similar to Shoemaker-Levy 9," said Leigh Fletcher, an astronomer at NASA's Jet Propulsion Lab in Pasadena, California. "We're all extremely excited."
The impact was discovered by amateur astronomer Anthony Wesley in Murrumbateman, Australia at about 1330 GMT on Sunday. Wesley noticed a black spot in Jupiter's south polar region (see image) – but he very nearly stopped observing before he saw it.
"By 1am I was ready to quit ... then changed my mind and decided to carry on for another half hour or so," he wrote in his observation report. Initially he suspected he was seeing one of Jupiter's moons or a moon's shadow on the planet, but the location, size and speed of the spot ruled out that possibility.
'Stroke of luck'
After checking images taken two nights earlier and not seeing the spot, he realised he had found something new and began emailing others.
"It was a fantastic stroke of luck," Orton told New Scientist.
Their team began observations at about 1000 GMT on 20 July, and after six hours of observing confirmed that the spot was an impact and not a weather event.
"It's completely unlike any of the weather phenomena that we observe on Jupiter," Orton says.
The first clue was a near-infrared image of the upper atmosphere above the impact site. An impact would make a splash like a stone thrown into a pool, scattering material in the atmosphere upwards. This material would then reflect sunlight, appearing as a bright spot at near-infrared wavelengths.
And that's exactly what the team saw. "Our first image showed a really bright object right where that black scar was, and immediately we knew this was an impact," Orton says. "There's no natural phenomenon that creates a black spot and bright particles like that."
Supporting evidence came from measurements of Jupiter's temperature. Thermal images also showed a bright spot where the impact took place, meaning the impact warmed up the lower atmosphere in that area.
The researchers have also found hints of higher-than-normal amounts of ammonia in the upper atmosphere. Extra ammonia had been churned up by the previous Shoemaker-Levy comet impact.
The Shoemaker-Levy impact also introduced some exotic chemistry into Jupiter's atmosphere. The energy from the collision fused some of the original atmospheric components into new molecules, such as hydrogen cyanide.
Scientists hope this new impact has done the same thing, since that would allow them to follow the new materials and learn how the atmosphere moves with time.
So what was the impactor? "Not a clue," Orton says. He speculates that it could have been a block of ice from somewhere in Jupiter's neighborhood, or a wandering comet that was too faint for astronomers to detect before the impact.
"We don't know if the impact was produced by a comet or an asteroid," agrees Franck Marchis, an astronomer at the University of California, Berkeley, and the SETI Institute, who was part of a team that observed the spot on Sunday with the Keck Observatory in Hawaii (see image). If the object was large enough to be visible before impact, current surveys of asteroids may not have been looking in the right direction to find it, he says, adding that future surveys will spot more of the solar system's uncatalogued objects.
Asteroid or comet
Spectra collected by various observatories may help identify what the impactor was, since a large amount of water at the impact location would hint at a comet as the source. "We will also compare the observations with those collected during [Shoemaker-Levy 9] 15 years ago," since that was a known comet, Marchis says.
Without having seen it, scientists can't tell how large the object was. "But the impact scar we're seeing is about the same size as one of Jupiter's big storms, Oval BA, Fletcher told New Scientist. "That, I believe, is about the size of the Earth."
Marchis says Jupiter may be protecting Earth from getting hit by such objects. "The solar system would have been a very dangerous place if we did not have Jupiter," he told New Scientist. "We should thank our Giant Planet for suffering for us. Its strong gravitational field is acting like a shield protecting us from comets coming from the outer part of the solar system."
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Have your say
Good thing its there to protect us from the boogey comets
I wouldn't be too quick to thank ol' Jinkers.
There's probably as much chance of Jupiter's gravity throwing an object *onto* a collision course with earth, as there is of it throwing something *off* such a course. Admittedly, anything that gets too close to Jupiter probably gets swallowed up completely.
Even worse would be if Jupiter fragmented a large single body into lots of smaller (but still significant) bodies. One of the pieces might do a bit less damage during an earth impact than the whole would have, but having more of them out there might increase the chance of an impact occuring at all. Old man Jupiter might be a mixed blessing.
Yikes! This makes that movie Deep Impact look like a walk in the park.
I think this would be a good opportunity to point out humanity's urgent need to diversify their planetary portfolio.
I don't think so. Every time Jupiter absorbs something, that's one less thing we have to worry about hitting Earth. Period. I will agree that in some circumstances it could bend the trajectory of something into us, but that's balanced by the trajectories that it bends away from us. (Jupiter's not aiming space debris at us.)
Well if Jupiter wasn't there there would be no astroid belt between mars and jupiter, Which is a potentional threat to us.
Maybe. But if Jupiter was not there, there would be a ZERO chance of Jupiter perturbing the object onto a collision course with us. In other words, if the comet has not crossed Earth orbit in the last 4.5 billion years, it is not likely too. But perturbations change the orbit...
While I agree in principal that Jupiter can throw things at us, I doubt that the chance of one getting thrown toward us is anything like the same as it getting deflected away, simply because there are going to be far more trajectories that won't hit earth than will. Think about it, across those distances Jupiter would have to deflect it into an arc that measures less than a degree, if we assume that it can only deflect it into a region with an arc of 90 degrees, thats 89:1 against it hitting us. That's without even factoring in the potential for it to simply eat the threat like it appears to have done to this object.
Jupiter helps remove potentially dangerous orbiting bodies. If a comet or asteroid approaches Jupiter closely enough, the tidal forces it experiences from Jupiter's gravity can break it into pieces, as happened for Comet Shoemaker-Levy. When this happens, energy goes into the object; this energy is drained away from the object's orbital energy. So the object slows down, and (depending on how much orbital energy it has lost) often ends up orbiting Jupiter instead of orbiting the Sun, as it originally was. Once an object is orbiting Jupiter, it is no longer a threat to Earth
One: There's no way the chances that it diverts an object at earth is even close to the chances it diverts it away o simply pulls it into orbit or directly into Jupitor.
Two: Just how do you imagine Jupiter would "fragment" an object. IF this rediculous claim was to ever happen the fragments would not escape Jupitors pull.
My advice, learn some basic physics.
It might be correct that there are fewer trajectories hitting Earth than avoiding ones.
but then an object coming this way is much less likely to originally have been on a hit trajectory if Jupiter wasn't there.
There are a lot more objects that can potentially have their course modified from 'avoid' to 'hit' than objects on course 'hit' that can be altered to 'avoid'.
I could argue further but my english sucks. I believe the probability of an object being modified from 'hit' to 'avoid' is the exact same as vice versa.
Considering we only had the technology to observe such phenomenon on the outer planets in the last two (or three?) decades, and we have already seen _two_ impacts that leave an EARTH-size scar on Jupiter, perhaps: a) we were just lucky to see a once-or-twice a century event, or b) Jupiter gets hit more often than thought
The disk of Jupiter has been observed and observable in sufficient detail to see this sort of high contrast scarring since about Cassini's time in the late 1600's. Telescopes were crude and cumbersome then but study of Jovian satellite mutual events was thought to be important for navigation so the planet was relatively well observed. A bogus satellite shadow should have been noticed - and perhaps they were. Roemer used Jovian satellite timings to estimate the speed of light in about 1670.
That said I expect that Jupiter does mop up a fair number of stray objects for us
How big would an object colliding with Jupiter need to be in order to make a spot that big? Are we talking asteroid-sized? Moon-sized? Or just a little bit of space debris?
The larger comet Shoemaker-Levy fragment hitting Jupiter was about 1 mile in diameter. This new impact seems a bit smaller, but not by much.
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