The dunes on Saturn's moon Titan, the largest moon in the Solar System, are composed primarily of organic sand grains. These sand grains are rich in carbon and nitrogen, the building blocks of life. They are derived from the precipitation of organic molecules from Titan's atmosphere and are subsequently weathered and transported by winds to form dunes. The presence of comet dust in Titan's atmosphere is not known, and therefore it is not considered a significant contributor to the composition of the dunes.