The Changing Jupiter
Jupiter is the fifth planet from the Sun and the largest planet in the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune. Jupiter is so large and relatively unchanging that it is considered rather constant in its appearance. As the planet gets struck repeatedly and continually with small space rocks, wide belts of the atmosphere are changing color, hotspots are vanishing and reappearing, and clouds are gathering over one part of Jupiter, while dissipating over another. The results were presented today by Glenn Orton, a senior research scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., at the American Astronomical Society's Division for Planetary Sciences Meeting in Reno, Nevada.
The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. he clouds are located in the tropopause and are arranged into bands of different latitudes, known as tropical regions. These are sub-divided into lighter-hued zones and darker belts. The interactions of these conflicting circulation patterns cause storms and turbulence.
"The changes we're seeing in Jupiter are global in scale," Orton said. "We've seen some of these before, but never with modern instrumentation to clue us in on what's going on. Other changes haven't been seen in decades, and some regions have never been in the state they're appearing in now. At the same time, we've never seen so many things striking Jupiter. Right now, we're trying to figure out why this is all happening."
Following the fading and return of a prominent brown-colored belt just south of the equator, called the South Equatorial Belt, from 2009 to 2011, the team studied a similar fading and darkening that occurred at a band just north of the equator, known as the North Equatorial Belt. This belt grew whiter in 2011 to an extent not seen in more than a century. In March of this year, that northern band started to darken again.
The team obtained new data from NASA's Infrared Telescope Facility and the Subaru Telescope on Mauna Kea that matched up that activity with infrared observations. Those data showed a simultaneous thickening of the deeper cloud decks, but not necessarily the upper cloud deck, unlike the South Equatorial Belt, where both levels of clouds thickened and then cleared up. The infrared data also resolved brown, elongated features in the whitened area called "brown barges" as distinct features and revealed them to be regions clearer of clouds and probably characterized by down welling, dry air.
There are also a series of blue-gray features along the southern edge of the North Equatorial Belt. Those features appear to be the clearest and driest regions on the planet and show up as apparent hotspots in the infrared view, because they reveal the radiation emerging from a very deep layer of Jupiter's atmosphere. Those hotspots disappeared from 2010 to 2011, but had reestablished themselves by June of this year, coincident with the whitening and re-darkening of the North Equatorial Belt.
While Jupiter's own atmosphere has been churning through change, a number of objects have hurtled into Jupiter's atmosphere, creating fireballs visible to amateur Jupiter watchers on Earth. Three of these objects - probably less than 45 feet in diameter - have been observed since 2010. The latest of these hit Jupiter on Sept. 10, 2012, although Orton and colleagues' infrared investigations of these events showed this one did not cause lasting changes in the atmosphere, unlike those in 1994 or 2009.
"It does appear that Jupiter is taking an unusual beating over the last few years, but we expect that this apparent increase has more to do with an increasing cadre of skilled amateur astronomers training their telescopes on Jupiter and helping scientists keep a closer eye on our biggest planet," Orton said. "It is precisely this coordination between the amateur-astronomy community that we want to foster."
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Global Upheaval image via NASA.