It will soon be spring on Saturn ... and it will last for the next eight years or so. To celebrate the slow passing of the seasons of the giant ringed planet, NASA has released four real-color images sent back by the Cassini space probe. The images not only show the seasonal changes, but also the mysterious vortex recently discovered at the south pole of Saturn’s largest moon, Titan.
Real color images from space are always a treat. Many people don’t realize that a lot of the glorious pictures of stars and planets that they see aren’t actually the way the subjects really look. Space isn’t just big, as Douglas Adams observed, it’s also very dim and blurry in places. We’re so used to seeing spectacular images from the Hubble telescope or planetary spacecraft we forget that it takes a lot more than pointing and shooting to create them.
If you’ve ever looked through a university-league telescope at a nebula or planet, the former looks like a faint patch of nothing rather than a glowing cloud and the latter comes across as a washed-out ball. That's because astronomical telescopes are more cameras than spy glasses. The breathtaking pictures that grace magazine covers and internet sites are time exposures where faint details are built up over minutes or even hours.
It’s a similar case with spacecraft. They’re designed to send back data, not just pretty pictures and many of the images we see are intended to bring out and highlight particular information. The images may have been taken in infrared or ultraviolet light to turn a fuzzy Venus into a swirl of clouds or they may use false color to provide contrast or to show information about temperature, structure or chemical composition.
The images released by NASA were taken by the Cassini probe from May to July of this year. The probe has been in orbit around Saturn for eight years, which is long enough to observe seasonal changes, though it would require a 30-year mission to observe a whole Saturnian year.
While these are true color images, the brightness has been somewhat enhanced because Saturn is so far from the Sun. Some of the images were only possible because Cassini has moved into a new orbit that sends it over the polar regions of Saturn and its moons.
Of particular interest in the images is the vortex that Cassini recently discovered at Titan’s south pole. The enigmatic vortex of yellow haze was photographed by Cassini in July, though it detected the phenomenon with its infrared mapping spectrometer on May 22. The vortex has been there since at least March and rotates faster than Titan itself. It seems to consist of air rising at the edges and sinking in the middle. Scientists are racing against time to find clues as to the nature of the vortex because winter is descending on Titan’s south pole and the area will be in darkness in a few years.
The image at the top of this page is a view taken from about 483,000 miles (778,000 km) from Titan, we see the giant moon passing in front of Saturn as it orbits about the planet every 16 days. Winter on Saturn’s northern hemisphere is turning to spring and the bluish tint in the atmosphere is fading in the north and increasing in the south. This effect is probably caused by the Sun’s ultraviolet light and enhanced by the same process that makes the Earth’s sky turns blue in the daytime.
Saturn is the second largest planet in the Solar System with a diameter of 74,500 miles (120,000 km) - eight times that of Earth and it has the largest rings of any planet. It’s a gas giant consisting largely of hydrogen and helium and the famous rings are made of icy moonlets orbiting too close to the planet to form a proper satellite due to tidal forces.
In the above image Titian is obscured by Saturn's rings. The dark band is caused by Saturn’s shadow. Even at a distance of 9 million miles (14.5 million km), the south polar vortex is visible. Titan is Saturn’s largest moon. With a diameter 3,200 miles (5,150 km), it is not only the Solar System’s second largest moon after Ganymede, but is also larger than the planet Mercury.
When the Cassini probe passed behind Titan’s night side at a distance of 134,000 miles (216,000 km) on June 6, 2012, it took this image showing the remarkable ring of color caused by Titan’s nitrogen/methane atmosphere scattering sunlight.
The above image taken by Cassini’s cameras on July 25, 2012, at a distance of about 64,000 miles (103,000 km) shows a clear view of Titan’s south polar vortex.
The Cassini probe is a joint NASA/ESA probe mission. Weighing 5,560 lb (2,523 kg), carries a battery of instruments and is powered by three radiothermal generators because at such a distance from the sun, nuclear power is the only current option for a craft of that size. Cassini was launched October 15, 1997 from the Cape Canaveral Air Force Station, Florida and is controlled from Jet Propulsion Laboratory in Pasadena, California. It was flung toward Saturn after two flybys of Venus and then Jupiter before arriving in orbit about the ringed planet on July 1, 2004.
The Cassini spacecraft also carried with it the ESA Huygens probe, which landed on Titan on January 14, 2005.
In the course of it’s mission, Cassini has discovered several new moons as well as making extensive surveys of Saturn’s structure, atmosphere, rings and magnetic field. After the completion of its original mission, NASA extended its stay to 2008 and renamed it the Cassini Equinox mission because it was now studying the planet during, as the name suggests, its equinox. Its mission was further extended until 2017 as the Cassini Solstice mission to study the Saturnian northern spring/southern autumn.
Due to fear of contaminating Titan, which may harbor life, the end of Cassini’s mission, will either to be deliberately crashed into Saturn or a moonlet, or flung into a heliocentric orbit.