Based upon a NASA press release, "Cassini Sees the Two Faces of Titan's Dunes", January 23, 2012.
Sand Dunes as a Dominant Landscape
Sand dunes are a dominant surface feature on Saturn's moon Titan. They cover about 13% of the moon's
surface - an area about the same size as the United States.
Information about Titan's sand dunes obtained by NASA's Cassini spacecraft show that the sand dunes on
Titan are very similar to the dunes covering the surface of Earth's major deserts. However, there are
some interesting differences.
What is a Sand Dune?
A sand dune is a hill of loose sand that has been deposited by wind. Sand dues are generally dynamic features.
They are moved by the wind and their shape is determined by wind direction and sand abundance. Over time the dunes can travel long distances. In areas where there is an abundant supply
of sand they can cover broad areas known as "dune fields" or "ergs".
What Kind of Sand is in Titan's Dunes?
The word "sand" refers to a particle size between 1/16 millimeter and 2 millimeters in diameter. It does
not imply a specific composition. Most sand dunes on earth are composed of quartz sand. However, Titan is a
gaseous planet and the sand in its dunes is thought to be composed of solid hydrocarbon. This hydrocarbon sand
is thought to have precipitated from Titan's atmosphere.
How Big are Titan's Sand Dunes?
Many of the sand dunes on Titan are very large. They can be 1 to 2 kilometers wide and hundreds of kilometers in
length. Many are over 100 meters tall.
Where are the Sand Dunes on Titan?
Most of the sand dunes on Titan are confined to a region within 30 degrees latitude of the moon's equator. South of
Titan's equator there is an abundant supply of mobile sand and the dunes there are large and
well developed. An example are the dunes of the Belet area shown at right.
North of Titan's equator the
supply of mobile sand is much lower and the dunes are smaller and less developed. An example are the dunes
of the Fensal area shown at right.
Titan's Eliptical Orbit and Sand Dunes
The change in dune character north and south of Titan's equator is thought to be caused by Saturn's eliptical orbit around the sun.
This elipitical orbit takes seven Earth years and causes Titan's southern hemisphere to have a very intense summer. This intense summer produces a dry
climate which facilitates the movement of loose sand grains and the formation of dunes.
The northern hemisphere has a less intense summer which is thought to allow more mosture in the soil. The moist
soil inhibits movement of sand grains by the wind and results in reduced sand dune development.
The distribution of lakes on Titan support this theory. Most of the lakes are in the northern hemisphere where the soil
moisture is thought to inhibit sand dune development.
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A Cassini spacecraft image of sand dunes in the Belet region of Titan, an area south of the equator where there is thought to be an abundant supply of mobile sand. The dunes are wide and separated by a trough that is covered by a thick blanket of sand. These Belet dunes resemble the linear sand dunes found in the Rub' al Khali area of Saudi Arabia (image below).
Satellite image of linear sand dunes in the Rib' al Khali of Saudi Arabia. Image by NASA's ASTER Science Team.
Cassini spacecraft Image of sand dunes in the Fensal region, north of Titan's equator. These dunes are thinner and more widely-separated when compared to dunes of the Belet region. They form in areas where the supply of mobile sand is limited. These dunes are similar to those found in the Kalahari Desert of Namibia.
Satellite image of linear sand dunes from the southwestern margin of the Kalahari Desert in Namibia. Image by NASA's ASTER Science Team.