A new analysis of radar data from the Cassini mission in a partnership between NASA, the European Space Agency (ESA) and the Italian Space Agency concerning Titan, the largest of Saturn’s moons, have revealed an extensive presence of dunes that show changes with the passage of time and are different depending on their latitude and altitude.

The dune fields occupy about 13% of Titan’s surface with a total area more or less equivalent to Canada. The dunes are formed in the equatorial region and in the northern hemisphere tend to be narrower. This may be due to the elliptical orbit of Saturn: Titan orbits Saturn and along with it around the Sun in an year that lasts for almost thirty Earth years. Every season on Titan lasts more than seven Earth years and because of Saturn’s elliptical orbit in the southern hemisphere summers are shorter but more intense. Consequently, the southern regions are drier and the sand can be transported more easily by the winds that create the dunes.

A confirmation of this hypothesis comes from the fact that lakes and seas of liquid methane and ethane are more common in the northern hemisphere, where the sand gets wet and is consequently more difficult to transport by winds.

The radar images of the region of Belet, in a lowland area, show wide dunes with thicker blankets of sand between them. The biggest Titan’s dune fields are of this type. The Earth dunes in the desert of Oman are of this type.

The dunes in higher latitude areas such as the ones in the region of Fensel tend to be thinner and more separated from each other. The Earth dunes of the Kalahari in South Africa and Namibia are of this type. This suggests that at high altitudes there’s little sand available to form dunes. The image shows a comparison between the two kinds of Titan dunes and the Earth ones in desert of Oman and Kalahari (Image NASA/JPL-Caltech, and NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team).

Despite these similarities, there are considerable differences between the Earth’s and Titan’s dunes. First of all their sizes: Titan’s dunes are gigantic by Earth standards because their average width is one or even two kilometers, their length can be hundreds of kilometers and their height is around one hundred meters.

Another difference is the dunes composition: the Earth’s dune sand is composed of silicates while the Titan’s sand is made of solid hydrocarbons that precipitate from the atmosphere. They aggregate into millimetre-sized grains through a process still unknown.

The understanding of the formation, shape, size and distribution of dunes on Titan is important to understand the climate and geology of this satellite which shows once more that it’s truly extraordinary.