Friday, November 2, 2012

Stormy Weather On Saturn

Saturn is probably the most beautiful member of our Sun's enchanting family of eight major planets. It is the second-largest planet in our Solar System, after Jupiter, and it is circled by 62 known moons, and myriads of dancing, tiny moonlets that are a mere 2 to 3 kilometers across. They are mostly icy objects, glittering both within and outside of Saturn's magnificent system of rings.

Saturn and Jupiter are our Solar System's two gas-giant planets. Both are denizens of the outer Solar System, and are primarily composed of extremely dense, deep gaseous atmospheres. Some planetary scientists think that the two immense worlds have no solid surface beneath their heavy envelopes of gas. However, other planetary scientists think that Jupiter and Saturn do have relatively tiny solid cores. The other two major planets that dwell in the outer regions of our Solar System are Uranus and Neptune. Uranus and Neptune are thought to have large cores composed of icy, rocky material, as well as gaseous envelopes that are not nearly as thick as those possessed by Jupiter and Saturn. Uranus and Neptune are the two ice-giant planets of the outer Solar System, and they are smaller than the gas-giants Jupiter and Saturn.

For many scientists and the public, Saturn's rings always steal the show. The rings are a collection of innumerable icy bits that range in size from that of minuscule smoke-sized particles to chunks as large as houses. These small orbiting icy objects interact with each other in an exquisite dance, and they are also effected by their planet's magnetosophere--which is the region of a planet's magnetic influence--as well as by the larger moons. The main rings create a very wide but unusually thin and ethereal expanse that is approximately 250,000 kilometers across but only tens of hundreds of meters deep. The origins and ages of the rings remain delightfully mysterious. Theories abound and vary greatly. Differing viewpoints suggest that the rings may be as young as 100 million years or as old as the 4.5 billion-year-old planet itself. Determining the age of the rings is an important scientific endeavor. This is because the answer to this elusive question will ultimately provide a fundamental and necessary clue to the origin and evolution of the Saturnian system itself. Although the rings have numerous attributes that make them appear to be quite young, they may have been around for as long as Saturn has.

Saturn's magnificent ring system is divided by astronomers into 5 main components: the G, F, A, B, and C rings, that are listed from the outermost to the innermost. Reality, however, is somewhat more complicated than this simple classification would indicate. These main divisions are subdivided into thousands of individual ringlets. The A, B, and C rings are easy to see, and are very wide. However, the F and G rings are slender and ethereal and very difficult to observe. There is also a large gap between the A ring and the B ring, which is termed the Cassini Division.

Although Saturn's ring system is the most famous and easiest to observe, all of the giant planets dwelling in the outer limits of our Solar System sport ring systems. However, the ring systems circling the other three giant planets are not nearly as spectacular as Saturn's. But, this doesn't mean that the ring systems of the other giant planets are uninteresting. Like Saturn, the other three outer planets also host a myriad of little dancing moonlets that orbit just beyond or very close to the rings, followed by an admirable retinue of larger moons.

On July 1, 2004 NASA's Cassini spacecraft swept into orbit around Saturn and began taking some remarkable pictures. Although Saturn appears to be a placid planet on the surface, Cassini showed that looks can be deceiving, when it imaged the "Great Springtime Storm" that blasted Saturn in early 2011. NASA announced the discovery of this immense tempest on October 25, 2012. The terrible storm sported a gigantic cloud cover as big as the entire Earth, as well as the "largest and hottest stratospheric vortex ever detected in our Solar System". At one point Cassini also detected on Saturn an "almost unbelievable"spike in regional temperature of 150 degrees Fahrenheit, which represents the biggest jump ever observed in our Solar System. Dr. Brigette Hesman, part of the Cassini team, noted in the October 26, 2012 online National Geographic News that "We were quite shocked when we detected the temperature change--nothing like that was ever observed before." Dr. Hesman is a research scientist at the University of Maryland.

Along with the dramatic temperature spike came an immense deposit of the hydrocarbon gas ethylene, which is a byproduct of methane, that had been previously observed only in trace amounts in the ringed planet's atmosphere. How this ethylene became so dramatically and suddenly abundant is a mystery.

"We know this was all caused by a big storm in the lower atmosphere," where temperatures are warm enough for water to condense and form clouds, Hesman continued to note.

The oval-shaped tempest formed when two warm spots in Saturn's ever-churning cloud deck collided and merged. The resulting storm was not visible to human eyes. However, it did shine brightly at infrared wavelengths. The tempest raged through Saturn's northern latitudes over the latter part of 2010 and most of 2011, and was the largest recorded maelstrom since 1903. Indeed, the storm grew so immense that it swept all the way across the entire planet, and actually caught its own tail. At its peak, the tempest--which produced extremely high winds and devastating flashes of intense lightning--formed a cloud cover that circled Saturn in a band that was 9,000 miles wide!

A Saturnian year is approximately equal to 30 Earth-years. Saturn is stricken by a major storm at roughly the same interval. The "Great Springtime Storm" arrived eleven years ahead of schedule and lingered for more than half a year. The visible storm spread within the cloud deck of Saturn's troposphere, and waves of energy shot up hundreds of miles. This created immense "beacons" of hot air, which pushed into the stratosphere. Although planetary scientists expected these beacons to disintegrate and cool down, by early 2011 they had instead clung together creating one immense vortex that for a short time was actually larger than Jupiter's famously enormous Great Red Spot. A bizarre soupy cauldron of hot gases was also seen encircling the enormous vortex.

The brilliant beacon is expected to fade away and eventually disappear by 2012. However, planetary scientists wonder what other surprises are in store on this beautiful, mysterious, puzzle of a giant planet. Two papers describing the vortex will be published in November 2012, one in the journal Icarus, the other in the Astrophysical Journal.