July 4, 2004: It didn’t take long for the Cassini spacecraft to start making discoveries. In orbit around Saturn for only a few days, Cassini has already captured images of Saturn’s giant moon Titan revealing never-before-seen details of the moon’s surface.
“Although the initial images appear bland and hard to interpret, we’re happy to report that we have indeed seen Titan’s surface with unprecedented clarity,” says JPL’s Dennis Matson, project scientist for the international Cassini-Huygens mission.
Right: A false-color image of Titan. Yellow areas correspond to hydrocarbon-rich regions; green areas are icier regions. A south polar methane cloud appears white. Note the circular feature, a possible impact crater, in the northern hemisphere. [More]
Titan’s dense atmosphere is opaque at most wavelengths, but Cassini’s visible and infrared mapping spectrometer takes pictures at wavelengths in which the atmosphere is clear. Near-infrared colors, some three times redder than the human eye can see, reveal what lies beneath the clouds.
“We’re seeing a totally alien surface,” says Elizabeth Turtle of the University of Arizona. “There are linear features, circular features, curvilinear features. These suggest geologic activity on Titan, but we really don’t know how to interpret them yet. We’ve got some exciting work cut out for us.”
In addition to seeing through Titan’s clouds, the visual and infra-red spectrometer is also able to sense specific minerals and chemicals; this is the first time scientists have been able to map the surface-mineralogy of Titan. Using hundreds of wavelengths, many of which have never been used in Titan imaging before, they are creating a global map showing distributions of hydrocarbon-rich regions and areas of icy material.
Says JPL’s Kevin Baines, Cassini science-team member: “At some wavelengths, we see dark regions of relatively pure water ice and brighter regions with a much higher amount of non-ice materials, such as simple hydrocarbons. This is different from what we expected.”
Also, he adds, “a methane cloud is visible near the south pole. It’s made of unusually large particles compared to Titan’s typical haze particles, suggesting a dynamically active atmosphere there.”
Above: This five-hour sequence of images, acquired on July 2, 2004, illustrates the evolution of a field of clouds near Titan’s south pole. The bright clouds, believed to be composed of methane, appear in generally the same area where Earth-based astronomers have previously detected clouds. Cassini also saw clouds in this region during its approach to Saturn. [More]
Since entering orbit, Cassini has also provided the first view of a vast swarm of hydrogen molecules surrounding Titan well beyond the top of Titan’s atmosphere. Cassini’s magnetospheric imaging instrument, first of its kind on any interplanetary mission, provided images of the huge cloud sweeping along with Titan in orbit around Saturn. The cloud is so big that Saturn and its rings would fit within it.
“The top of Titan’s atmosphere is being bombarded by highly energetic particles in Saturn’s radiation belts, and that is knocking away this neutral gas,” explains Stamatios Krimigis of the Johns Hopkins Applied Physics Laboratory, principal investigator for the magnetospheric imager. “In effect, Titan is gradually losing material from the top of its atmosphere, and that material is being dragged around Saturn.”
Right: Surrounding Titan, a globular cloud of gas some 70,000 kilometers (43,496 miles) in diameter. [More]
These first images of Titan and its environs are just a taste of what’s to come. “We look forward to future, much closer flybys and use of radar for much greater levels of surface detail,” notes Dennis Matson.
The study of Titan, Saturn’s largest moon, is one of the major goals of the Cassini-Huygens mission. Titan may preserve in deep-freeze many chemical compounds that preceded life on Earth. Friday’s flyby at a closest distance of 339,000 kilometers (210,600 miles) provided Cassini’s best look at Titan so far, but over the next four years, the orbiter will execute 45 Titan flybys as close as approximately 950 kilometers (590 miles). This will permit high-resolution mapping of the moon’s surface with an imaging radar instrument, which can see through the opaque haze of Titan’s upper atmosphere.
In January 2005, the Huygens probe that is now attached to Cassini will descend through Titan’s atmosphere to the surface.
