What Created a Pacific-Ocean Sized Impact on Jupiter? New Hubble ‘CSI’ Images Show a Massive Asteroid

6a00d8341bf7f753ef0115722a12f4970b-320wi The images shown below are further evidence that space itself is an action movie (or at least that God watches Michael Bay movies), an explosion the size of the Pacific ocean had scarred Jupiter. The explosion occurred on July 19 when an object slammed into the planet, and although Jupiter has no solid ground the gas can still get thick enough for things like "impacts" and "KABOOM" to happen.

The Jupiter impact event is another big red line underscoring Stephen Hawking's theory that one of the major factors in the possible scarcity of intelligent life in our galaxy is the high probability of an asteroid or comet colliding with inhabited planets. We have observed, Hawking pointed out in his lecture Life in the Universe, the collision of a comet, Schumacher-Levi, with Jupiter, which produced a series of enormous fireballs, plumes many thousands of kilometers high, hot "bubbles" of gas in the atmosphere, and large dark "scars" on the atmosphere which had lifetimes on the order of weeks. The  July 19th event is a weak second place, but still totally awesome (and awesome if projected to a planet called Earth).

One of the most interesting things about the explosion is that it was detected by an amateur astronomer.  We might have a lot of super-slick space-searching sensors, but there's still a hell of a lot more space to watch than we have equipment to watch it – which is why Australian hobbyist Anthony Wesley was the first to see it.  The information spread online, and Berkeley astronomer changed his plans for pre-booked time on the Hawaiian Keck II telescope, abandoning his planet-hunting to get a closer look.  A much cooler use of internet communications than tweeting about sandwiches.

The resulting scar on the surface of Jupiter shows up as a dark patch in visible light, but a very bright spot in infrared, caused by a radical rearrangement of gases in the region of the detonation.  The bright spot will also allow scientists to examine the motion of gases in Jupiter's atmosphere, test theories developed during past impacts, and generally think "Wow, this stuff we do is pretty awesome, isn't it?"

Many more tools will soon be brought to bear on this huge planetary event.  Hubble will be getting in on the action, bringing its brand-new wide angle camera to bear, while Berkeley will be bringing laser guide stars to bear (artificial star-signals created in the atmosphere by laser beam, allowing the use of adaptive optic telescopes which can correct for the atmosphere's effects on light).  So even the tools being used to look at this are awesome.

As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life – animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).

But back to Professor Hawking, he of black-hole radiation fame: How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact? Galactic history suggests it might be a common occurrence. Our cold comfort comes from the adjective "galactic" -that's a hugely different time perspective that our biblical three score and ten.

2-hubbleimages The astronomers who compared Hubble images of both collisions say the culprit may have been an asteroid about 1,600 feet (500 meters) wide. The images, therefore, may show for the first time the immediate aftermath of an asteroid, rather than a comet, striking another planet.

The Jupiter bombardments reveal that the solar system is a rambunctious place, where unpredictable events may occur more frequently than first thought. Jupiter impacts were expected to occur every few hundred to few thousand years. Although there are surveys to catalogue asteroids, many small bodies may still go unnoticed and show up anytime to wreak havoc.

"This solitary event caught us by surprise, and we can only see the aftermath of the impact, but fortunately we do have the 1994 Hubble observations that captured the full range of impact phenomena, including the nature of the objects from pre-impact observations" says astronomer Heidi Hammel of the Space Science Institute in Boulder, Colo., leader of the Jupiter impact study.

In 2009 Hammel's team snapped images of the debris field with Hubble's recently installed Wide Field Camera 3 and newly repaired Advanced Camera for Surveys.

The analysis revealed key differences between the two collisions (in 1994 and 2009), providing clues to the 2009 event. Astronomers saw a distinct halo around the 1994 impact sites in Hubble ultraviolet (UV) images, evidence of fine dust arising from a comet-fragment strike. The UV images also showed a strong contrast between impact-generated debris and Jupiter's clouds.

Hubble ultraviolet images of the 2009 impact showed no halo and also revealed that the site's contrast faded rapidly. Both clues suggest a lack of lightweight particles, providing circumstantial evidence for an impact by a solid asteroid rather than a dusty comet. 

The elongated shape of the recent impact site also differs from the 1994 strike, indicating that the 2009 object descended from a shallower angle than the SL9 fragments. The 2009 body also came from a different direction than the SL9 pieces.

Team member Agustin Sanchez-Lavega of the University of the Basque Country in Bilbao, Spain, and colleagues performed an analysis of possible orbits that the 2009 impacting body could have taken to collide with Jupiter. Their work indicates the object probably came from the Hilda family of bodies, a secondary asteroid belt consisting of more than 1,100 asteroids orbiting near Jupiter.

The 2009 strike was equal to a few thousand standard nuclear bombs exploding, comparable to the blasts from the medium-sized fragments of SL9. The largest of those fragments created explosions that were many times more powerful than the world's entire nuclear arsenal blowing up at once.

The recent impact underscores the important work performed by amateur astronomers. "This event beautifully illustrates how amateur and professional astronomers can work together," notes Hammel.

Occasional dark spots have appeared on Jupiter throughout the history of sky watching. Observing records of the planet are filled with references to spots, including "white spots," "peculiar spots," and "well-defined spots." Only a handful may have described possible Jupiter strikes.

In 1686, the Italian astronomer Giovanni Cassini reported a dark spot on Jupiter that was roughly the size of the largest SL9 impact. Nearly 150 years later, in 1834, British astronomer George Airy independently reported a dark feature in Jupiter's southern belts that looked nearly four times as large as shadows cast on the planet by the Galilean moons. But the then crude telescopes prevented sky watchers from probing the nature of those spots.

The study by Hammel's team appeared in the June 1 issue of The Astrophysical Journal Letters.

Luke McKinney and Casey Kazan via the ESA/Hubble Information Centre


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