On November 9th 2010, Jupiter’s ‘missing’ South Equatorial Belt (SEB) showed signs of a spectacular, violent and eruptive revival, initiating a chain of events that will ultimately revive the typical brown colour of the belt.  A huge plume of bright material erupted in the SEB, prompting us to scramble for time on Gemini, Keck, IRTF and VLT to study this unprecedented opportunity to observe a rare and mysterious phenomenon caused by the planet's winds and cloud chemistry.

Stripes Are Back in Season on Jupiter

Earlier this year, amateur astronomers noticed that the long-standing stripe, known as the South Equatorial Belt (SEB), just south of Jupiter's equator, had turned white (see the Hubble space telescope image comparison on the right, noting the missing belt). In early November, amateur astronomer Christopher Go of Cebu City in the Philippines observed a prominent bright spot in the unusually whitened belt, piquing the interest of professional and amateur astronomers around the world.  After follow-up observations with NASA's Infrared Telescope Facility (IRTF), the 10-meter Keck telescope and the 8-meter Gemini telescope, all atop Mauna Kea in Hawaii, scientists now believe the stripe is making a comeback.

NASA's Infrared Telescope Facility False obtained this false-color composite image on Nov. 16 (right). The prominent region just to the left of the center, expanded in the insert, shows the region of the South Equatorial Belt outbreak. In the coming weeks, further outbreaks are expected to take place to the west (left) of those seen in this image. The clear atmospheric regions (in red) will begin to fill this latitude band at the same time as the dark brown color typical of this region returns.

Astronomers announced first-glimpse images of the reappearing stripe Nov. 9.  "The reason Jupiter seemed to 'lose' this band — camouflaging itself among the surrounding white bands — is that the usual downwelling winds that are dry and keep the region clear of clouds died down," said Glenn Orton, a research scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "One of the things we were looking for in the infrared was evidence that the darker material appearing in visible light was actually the start of clearing in the cloud deck, and that is precisely what we saw."

This white cloud deck is made up of white ammonia ice. When the white clouds float at a higher altitude, they obscure the view of the lower brown clouds. Every few decades or so, the South Equatorial Belt turns completely white for perhaps one to three years, an event that has puzzled scientists for decades. This extreme change in appearance has only been seen with the South Equatorial Belt, making it unique to Jupiter and to the entire solar system.

The bright storm that Go observed in the faded belt was quite unusual, said Imke de Pater, UC Berkeley professor of astronomy.  "At infrared wavelengths, images in reflected sunlight show that the spot is a tremendously energetic 'outburst,' a vigorous storm that reaches extreme high altitudes," de Pater said. "The storms are surrounded by darker areas, bluish-grey in the visible, indicative of 'clearings' in the cloud deck."

To confirm the presence of such clearings, the team obtained data at longer wavelengths (5 micron) sensitive to thermal emission from Jupiter’s deep atmosphere. These data confirm that the visibly dark material indeed is being seen through holes in the cloud deck, "perhaps signaling the start of the SEB revival," added Glenn Orton. 

The white band wasn't the only change on the big, gaseous planet. At the same time, Jupiter's Great Red Spot became a darker red color. Orton said the color of the spot — a giant storm on Jupiter that is three times the size of Earth and a century or more old — will likely brighten a bit again as the South Equatorial Belt makes its comeback.

This false-color image, taken Nov. 11 by the Keck telescope (left), shows sunlight reflected off Jupiter's upper cloud deck — the same clouds that are seen in visible light. The bright spot in the South Equatorial Belt is the outbreak where winds are lofting particles to high altitudes. Click here for larger downloadable image and detailed caption and credits. (Credit: UC Berkeley, University of Toronto, University of San Carlos, Philippines)

Scientists are particularly interested in this event because it’s the first time they've been able to use modern instruments to determine the details of the chemical and dynamical changes of this phenomenon.  "These observations may help to unravel the mystery of why this transition occurs, and may allow us to understand the longevity of Jupiter's belt/zone structure," added Leigh Fletcher, a scientist at Oxford University in England.

The event also signifies another close collaboration between professional and amateur astronomers. The amateurs, located worldwide, are often well equipped with instrumentation and are able to track the rapid developments of planets in the solar system. These amateurs are collaborating with professionals to further study the changes that are of great value to scientists and researchers everywhere.

"I was fortunate to catch the outburst," Go said. "I had a meeting that evening, and it went late. I caught the outburst just in time as it was rising. Had I imaged earlier, I would not have caught it."

Go witnessed the disappearance of the stripe earlier this year, and in 2007 he was the first to catch the stripe's return. "I was able to catch it early this time around because I knew exactly what to look for," he said.

Since the discovery of the first spot, there have been several more outbreaks of varying strengths. The SEB revival is happening fast, with violent eruptions, de Pater said.  Observing this event carefully may help to refine the scientific questions that will be posed by NASA’s Juno spacecraft, due to arrive at Jupiter in 2016, and a larger mission to orbit Jupiter and explore its satellite Europa after 2020.  More observations at near- and mid-infrared wavelengths are planned for the coming weeks.

Image Captions:

Keck Images:  False color images of Jupiter and the SEB outbreak taken with the 10-meter W.M. Keck telescope in Hawaii on UT November 11, 2010, just 2 days after the initial discovery of the "outbreak". This false color composite is constructed from images taken in narrow-band filters centered at 1.21 micron (green), 1.58 micron (red), and 1.65 micron (blue). At 1.21 and 1.58 micron we see sunlight reflected off Jupiter's upper cloud deck - the same clouds that are seen in visible light. The narrow band image at 1.65 micron shows sunlight reflected back from hazes just above these clouds. The bright "spot" in the SEB is the outbreak where winds are lofting particles to high altitudes. Image Credit: James Graham (University of California, Berkeley and UofToronto/Dunlap Institute), Shelley Wright, Imke de Pater, Michael Wong (University of California, Berkeley). Christopher Go (University of San Carlos, Philippines) sharpened the images slightly using the RegiStax software, developed by Cor Berrevoets.

IRTF Images:  False color images of Jupiter and the SEB outbreak taken with the 3-meter NASA Infrared Telescope Facility in Hawaii on UT November 16, 2010. This image is a false color composite at three wavelengths that probe diagnostic altitudes in Jupiter's atmosphere: 1.58 microns (blue) sensitive to sunlight reflected from Jupiter's main cloud deck - also detected in visible light; 4.00 micron (green) detects sunlight reflected from higher-altitude particles well above the main deck; and 4.85 (red) micron detects the thermal emission arising from the tops of Jupiter's clouds, with the hottest emissions coming from the deepest atmosphere, and signifying regions with minimal overlying cloud cover. The prominent region just to the left of the center, and expanded in the insert, shows the region of the South Equatorial Belt (SEB) outbreak. The initial outbreak is identified at the upper right, with a second outbreak to the lower left. Between them, in red, is a region of clear atmosphere, probably the result of downwelling from the easternmost plume. In the coming weeks, further outbreaks are expected to take place to the west (left) of those seen in this image. The clear atmospheric regions (in red) will begin to fill this latitude band at the same time as the dark brown color typical of this region returns. Image credit: Glenn Orton, Padma Yanamandra-Fisher, Gregorio Villar (Jet Propulsion Laboratory, California Institute of Technology), David Griep (Institute for Astronomy, University of Hawaii), Leigh Fletcher (University of Oxford), Imke de Pater and Michael Wong (University of California, Berkeley).