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What whacked Jupiter? A giant meteor

Scientists say a huge meteor created the fireball that was spotted on Jupiter two weeks ago, and they also explain what happened to some of the giant planet's stripes.
Image: Flash aftermath on Jupiter
A natural-color photo of Jupiter, taken June 7, shows no telltale cloud of debris left behind by a meteor flash on June 3. The inset image at right is a close-up of the area where the flash occurred.NASA
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The mystery fireball that smacked into Jupiter on June 3 has been identified as a giant meteor that plunged into the planet's atmosphere and burned up high above its cloud tops, according to new observations from the Hubble Space Telescope.

The cosmic intruder did not dive deep enough into Jupiter's atmosphere to explode, which scientists said explains the lack of any telltale cloud of debris, as was seen in previous Jupiter collisions. Hubble astronomers described the meteor's size as "giant" in a Wednesday announcement.

"We suspected for this 2010 impact there might be no big explosion driving a giant plume, and hence no resulting debris field to be imaged," Heidi Hammel, a veteran Jupiter observer at the Space Science Institute in Boulder, Colo., said in a statement. "There was just the meteor, and Hubble confirmed this."

The meteor was huge, but not as large as the object that struck Jupiter in July 2009, or the shattered comet  fragments that hit the gas giant planet in 1994, researchers said. [Gallery: Jupiter's 2009 crash.]

The new Hubble observations also allowed scientists to get a close-up look at changes in Jupiter's atmosphere, following the seeming disappearance of the dark Southern Equatorial Belt, or SEB, several months ago.

In the latest Hubble view, a slightly higher altitude layer of white ammonia ice crystal clouds appears to obscure the deeper, darker belt clouds. "Weather forecast for Jupiter's South Equatorial Belt: cloudy with a chance of ammonia," Hammel said.

The researchers predict that these ammonia clouds will likely clear out in a few months, as it has typically done in the past.

Jupiter gets whacked (again)
The tale of Jupiter's latest cosmic hit is one that kept scientists guessing until now.

It was Australian amateur astronomer Anthony Wesley who first saw the flash at 4:31 p.m. ET on June 3, while watching a live video feed of Jupiter from his telescope. Meanwhile, in the Philippines, amateur astronomer Chris Go confirmed the discovery from his own simultaneous video recording of the transitory event.

Astronomers around the world determined that an object must have whacked the gas giant in order to unleash a flash of energy that was bright enough to be seen 400 million miles (643.7 million kilometers) away. But with no visible scar or debris cloud from the impact, there was no telling how deep the object penetrated into the atmosphere.

The Hubble Space Telescope's sharp vision and ultraviolet sensitivity was called into action to seek out any traces of the aftermath of the cosmic collision.

Images taken on June 7 — a little over three days after the flash was discovered — showed no sign of debris above Jupiter's cloud tops. That suggests the object did not descend beneath the clouds and explode as a fireball, astronomers said.

"If it did, dark sooty blast debris would have been ejected and would have rained down onto the cloud tops, and the impact site would have appeared dark in the ultraviolet and visible images due to debris from an explosion," Hammel explained. "We see no feature that has those distinguishing characteristics in the known vicinity of the impact, suggesting there was no major explosion and fireball."

Jupiter impacts of times past
Dark smudges marred Jupiter's atmosphere after pieces of the comet Shoemaker-Levy 9 slammed into the planet in 1994. A similar phenomenon occurred more recently in July 2009, when a suspected asteroid estimated to be about 1,600 feet (500 meters) wide collided with Jupiter.

This latest cosmic interloper is estimated to be only a fraction of the size of these previous impactors.

The two-second-long flash of light in the videos was created by the same physics that causes a meteor or "shooting star" on Earth. A shock wave is generated by ram pressure as the meteor speeds into the planet's atmosphere, heating the impacting body to a very high temperature.

As the hot object streaks through the atmosphere, it leaves behind a glowing trail of superheated atmospheric gases and vaporized meteor material that then rapidly cools and fades in the span of only a few seconds.

Though astronomers are still uncertain about the rate of such large meteoroid impacts on the planets in our solar system, it is estimated that the smallest detectable events may happen as frequently as every few weeks.

"It's difficult to even know what the current impact rates are throughout the solar system," said Amy Simon-Miller of NASA's Goddard Space Flight Center in Greenbelt, Md., the principal investigator on the Jupiter observation. "That's partly why we are so excited by the latest impact. It illustrates a new capability that can be exploited with increased monitoring of Jupiter and the other planets."

Even when impacts are detected, they can sometimes be misread.

"The meteor flashes are so brief they are easily missed, even in video recordings, or perhaps misidentified as detector noise or cosmic ray hits on imaging devices," said research team member Mike Wong of the University of California at Berkeley.

Image: Jupiter stripes
A comparison of Jupiter's disk from July 23, 2009, and June 7, 2010, shows how the planet's stripes have changed. The earlier image also highlights a

Case of the missing cloud belt
As for Jupiter's missing cloud belt, Hubble scientists said the space telescope's new photos showed all the warning signs of an impending disappearance of the planet's Southern Equatorial Belt.

The clearing of the ammonia cloud layer should begin with a number of dark spots like those seen by Hubble along the boundary of the south tropical zone.

"The Hubble images tell us these spots are holes resulting from localized downdrafts taking place," Simon-Miller said. "We often see these types of holes when a change is about to occur."

"The SEB last faded in the early 1970s," Simon-Miller added. "We haven't been able to study this at this level of detail before. The changes of the last few years are adding to an extraordinary database on dramatic cloud changes on Jupiter."