About a week ago, a bright white storm emerged on Saturn’s northern hemisphere, and amateur astronomer/planet astrophotographer extraordinaire Anthony Wesley from Australia has captured a few images of it. “This is the brightest Saturn storm in decades,” Anthony said on his website, Ice In Space. “If you get a chance to see it visually then take it, as it may be one of the rare “Great White Spot” (GWS) outbreaks on Saturn.”
Great White Spots, or Great White Ovals occur periodically on Saturn, and are usually large enough to be visible by telescope from Earth by their characteristic white appearance. The spots can be several thousands of kilometers wide.
Jupiter has a few mysteries these days. Between an equatorial belt that has gone missing and an impact that didn’t leave a mark, astronomers decided they needed to put the Hubble Space Telescope on the case. New and detailed observations from the venerable space telescope have provided some insights into these two recent puzzling events.
At 22:31 (CEST) on June 3, 2010 Australian amateur astronomer Anthony Wesley saw a two-second-long flash of light on the disc of Jupiter, captured from a live video feed from his telescope. In the Philippines, amateur astronomer Chris Go confirmed that he had simultaneously recorded the transitory event on video. Wesley was also the discoverer of the now world-famous July 2009 impact.
Astronomers around the world suspected that something significant must have hit the giant planet to unleash a flash of energy bright enough to be seen here on Earth, about 770 million kilometers away. But they didn’t know how just how big it was or how deeply it had penetrated into the atmosphere. Over the past two weeks there have been ongoing searches for the “black-eye” pattern of a deep direct hit like those left by former impactors.
Astronomers turned Hubble’s Wide Field Camera 3 aboard the NASA/ESA Hubble Space Telescope on June 7, and found no sign of debris above Jupiter’s cloud tops. This means that the object didn’t descend beneath the clouds and explode as a fireball. If it had, then dark sooty blast debris would have been ejected and would have rained down onto the clouds.
Instead the flash is thought to have come from a giant meteor burning up high above Jupiter’s cloud tops, which did not plunge deep enough into the atmosphere to explode and leave behind any telltale cloud of debris, as seen in previous Jupiter collisions.
“The cloud tops and the impact site would have appeared dark in the ultraviolet and visible images due to debris from an explosion,” said team member Heidi Hammel of the Space Science Institute in Boulder, Colorado. “We can see no feature that has those distinguishing characteristics in the known vicinity of the impact, suggesting there was no major explosion and no ‘fireball’.”
Dark smudges marred Jupiter’s atmosphere when a series of fragments of Comet Shoemaker-Levy 9 hit Jupiter in July 1994, and a similar dark area formed in July 2009 when a suspected asteroid slammed into Jupiter. The latest intruder is estimated to be only a fraction of the size of these previous impactors and is thought to have been a meteor.
So, Wesley and Go were fortunate to have spotted the flash.
“Observations of these impacts provide a window on the past — onto the processes that shaped our Solar System in its early history,” said team member Leigh Fletcher of the University of Oxford, UK. “Comparing the two collisions — from 2009 and 2010 — will hopefully yield insights into the types of impact processes in the outer Solar System, and the physical and chemical response of Jupiter’s atmosphere to these amazing events.”
Since Hubble was now trained on Jupiter, astronomers used the opportunity to get a close-up look at changes in Jupiter’s atmosphere following the disappearance of the dark cloud feature known as the Southern Equatorial Belt several months ago.
In the 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 Southern Equatorial Belt: cloudy with a chance of ammonia,” Hammel said.
The team predicts that these ammonia clouds should clear out in a few months, as they have done in the past. 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. We often see these types of holes when a change is about to occur,” said Amy Simon-Miller from Goddard Space Flight Center. .
“The Southern Equatorial Belt last faded in the early 1970s. We haven’t been able to study this phenomenon at this level of detail before,” Simon-Miller added. “The changes of the last few years are adding to an extraordinary database on dramatic cloud changes on Jupiter.”
When amateur astronomer Anthony Wesley from Australia saw a dark spot the size of the Pacific Ocean appear on Jupiter through his telescope on July 19, 2009, this started a flurry of astronomic activity, with other telescopes quickly slewing to take a look. It didn’t take long for other astronomers to confirm Jupiter had been hit by an object, either an asteroid or a comet. Of course, the world’s most famous telescope, Hubble, zeroed in on this unexpected activity on Jupiter, and luckily, the telescope had been recently updated with a new Wide Field Camera 3 and newly repaired Advanced Camera for Surveys. Astronomers have now released a series of images from Hubble which may show for the first time the immediate aftermath of an asteroid striking another planet.
Astronomers have witnessed this kind of cosmic event before, but from a comet. Similar scars had been left behind during the course of a week in July 1994, when more than 20 pieces of Comet P/Shoemaker-Levy 9 (SL9) plunged into Jupiter’s atmosphere. The 2009 impact occurred during the same week, 15 years later.
But comparing Hubble images of both collisions, astronomers say the culprit was likely an asteroid about 1,600 feet (500 meters) wide.
“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.
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 asteroid 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,” said Hammel.
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.
The study by Hammel’s team appeared in the June 1 issue of The Astrophysical Journal Letters.