“Bottom line, we don’t know exactly what the sand is and we don’t know how it got there,” says Ralph Lorenz at John Hopkins University. We know very little about Titan’s surface, which is why NASA’s Dragonfly mission will land near the dunes in 2036 searching for the building blocks of life.
Titan is covered in carbon-bearing material observes Lorenz — “it’s a giant factory of organic chemicals. We are carbon-based life, and understanding how far along the chain of complexity towards life that chemistry can go in an environment like Titan will be important in understanding the origins of life throughout the universe.”
Vast dunes of of tiny particles of carbon cover more than 13 percent of Titan’s surface, making them the second most dominant landform on Titan, stretching over an area of 4 million square miles (10 million square kilometers), or about the surface area of the United States. Scientists think the sand on Titan is not made of silicates as on Earth, but of solid hydrocarbons, precipitated out of the atmosphere. These have then aggregated into grains 0.04 inch in size by a still unknown process.
NASA’s Cassini spacecraft detected the signature of acetylene ice in the same regions as the dunes on Titan, prompting Ralf Kaiser at the University of Hawai’i at Mānoa and colleagues to perform an experiment to see if this ice could be chemically converted into complex organic molecules, reports Leah Crane at New Scientist. They bombarded acetylene ice in a laboratory with high-energy radiation similar to the cosmic rays that propagate through the galaxy, then heated the ice up until it sublimated so they could determine its final makeup.
Kaiser found that cosmic rays hitting the ice did cause it to react chemically to create the organic molecules we see in Titan’s dunes. These molecules are also likely created in the atmosphere, so they could come from there as well, says Ralph Lorenz at Johns Hopkins University in Maryland.
“Understanding how the dunes form as well as explaining their shape, size and distribution on Titan’s surface is of great importance to understanding Titan’s climate and geology because the dunes are a significant atmosphere-surface exchange interface”, says Nicolas Altobelli, ESA’s Cassini-Huygens project scientist. “In particular, as their material is made out of frozen atmospheric hydrocarbon, the dunes might provide us with important clues on the still puzzling methane/ethane cycle on Titan, comparable in many aspects with the water cycle on Earth.”
Though similar in shape to the linear dunes found on Earth in Namibia or the Arabian Peninsula, Titan’s dunes are gigantic by our standards –on average 1 to 2 kilometers wide, hundreds of kilometers long and around 100 meters high with their size and spacing vary across the surface, betraying the environment in which they have formed and evolved.
Image credit : NASA/ESA/IPGP/Labex UnivEarthS/University Paris Diderot