Titan's Mysteries Revealed

Dunes on Titan
This radar image of Shangri-La on Saturn's moon Titan shows hundreds of sand dunes (dark lines snaking across the surface). They are formed by wind acting on grains of hydrocarbons on the moon's surface. NASA/JPL-Caltech/ASI/Universite Paris-Diderot

Ever been hiking in the Badlands of South Dakota? If you have, you know this region has a rugged terrain surrounded by miles and miles of grasslands. Once you're in the Badlands, however, you're surrounded by layered rock formations, gullies, and canyons. All these features are sculpted by the action of the wind and flowing water, and you can literally count the layers of rock that have been shaped and uncovered by the action of erosion. You can also find sand dunes there, deposited by the ever-changing winds that blow there.

Dunes aren't unique to the Badlands, or even to planet Earth. There are dunes on Mars, made of sand and dust deposited by the thin, but constant Martian winds. It turns out that Venus has dune fields, as well.

Titan: Dune World

Way out in the outer solar system, Saturn's largest moon Titan has dunes, too. You may have heard of Titan. It's the largest moon orbiting the ringed planet Saturn. It's a frigid place made of water and rock, but covered with nitrogen ice and methane lakes and rivers. Temperatures on the surface reach a distinctly chilly -178 degrees Celsius (-289F). It's named for characters in Greek mythology, the Titans. They were the children of Ouranos and Gaia. 

Who would have thought that this distant little world with the ancient name would have lakes, rivers, badlands and dunes of its own? No one expected to find any of these things when the Cassini Mission began studying Titan. When the mission's Huygens probe landed on the chilly surface, planetary scientists were amazed to see these features. Continued studies with Cassini instruments that can peer through Titan's thick clouds have revealed more details about the surface features on Titan. The dunes are long, linear deposits of surface material that stretch across the landscape.

A hiker on Titan (dressed in a spacesuit to keep her warm and toting along oxygen tanks and other equipment) would find these long undulating patterns to be quite rugged, too. The latest set to be discovered exist in a region called Shangri-La. 

What Are Titan's Dunes Made Of?

The dune fields of Titan first showed up in a radar image taken by the Cassini spacecraft, sent to orbit Saturn and take images of the planet, its rings, and moons. They lie along Titan's equatorial region and are made not of sand, as dunes would be here on Earth, but of grains of hydrocarbon materials. These carbon-based compounds exist in Titan's atmosphere, and from time to time they "rain out" and settle onto Titan's frigid surface.

How Are Titan's Dunes Made?

On Earth, dunes are made by the action of the winds. They blow sand particles and dust along the surface and sculpt them into dunes that hug the high and low areas of the landscapes where they exist. The same actions are at work on Titan. Winds blow the hydrocarbon particles along and eventually deposit them along the surface contours. Once a dune is deposited, it's not stuck there forever. Just as on Earth, dunes on Titan can be moved along at the whim of the winds. This makes dunes on any world dynamic and ever-changing features. The Mountains of Xanadu Annex

The dunes aren't the only new surface features spotted on Titan. Cassini's radar also found mountainous terrains in a region called Xanadu Annex. Xanadu is a region first spotted by Hubble Space Telescope and the first surface feature to be recognized beneath Titan's thick clouds. The annex appears to be another similar region but scattered with mountain ranges. Planetary scientists think that Xanadu and its annex are among the oldest surfaces on Titan. They could well be part of the original icy crust that formed on this world early in its history.

Using Radar Imaging to Study Titan

Because Titan is covered with clouds, conventional cameras can't 'see through' to the surface. However, radar waves pass through clouds with no problems (as many drivers on Earth have found as they got caught in radar speed traps along busy highways, even on cloudy days). So, the spacecraft uses a technique called "synthetic aperture radar" to beam radar signals to the surface of Titan. They bounce back to the craft, giving exact information about the height of features on the surface, as well as other information. So, while Cassini's images aren't exactly what the eye would "see", they do show planetary scientists useful information about the landscape on Titan.

Cassini's Titan Studies

The Cassini Mission is focusing much of its attention on the lakes and seas that cover large areas of the surface in Titan's northern regions. This long-lived mission will come to an end in 2017. It arrived at the ringed planet in 2004 and dropped a probe to Titan (called Huygens) in 2005. The lander measured the temperatures in the atmosphere and on Titan's surface and sent back the first-ever images of the frozen moon.

Over the course of the mission, the Cassini spacecraft has made detailed studies of Saturn's rings, its atmosphere, and flow up-close to the moons Dione, Enceladus, Hyperion, Iapetus, and Rhea. At Enceladus, it actually flew through plumes of ice crystals jetting out from an ocean beneath that moon's surface. Cassini will end with a plunge into Saturn's atmosphere in September 2017.