Astronomers have produced the first global map of the geology of Titan providing a complete look at the different environments present on the surface of this moon of Saturn. The paper, published in Nature Astronomy, highlights six key different environments and how the methane cycle shapes them.

Like water shapes Earth, on the way-below-freezing surface of Titan, it’s methane that rains down, creates rivers and lakes, and then evaporates back into the atmosphere. The combination of this cycle with winds, chemical reactions, and temperature differences creates complex environments across Titan.

“Most of the surface is covered by organic materials, particularly plains (65 percent) and dunes (17 percent),” lead author Dr Rosaly Lopes of NASA’s Jet propulsion Laboratory told IFLScience. “These are formed, we think, by organic materials falling down from the atmosphere, and being moved around by wind. So this tells us that winds have been very important in shaping the surface of Titan.” 

There is clear latitudinal variation between the different environments. The dunes are found near the equator, the organic plains are at mid-latitudes, and the poles are home to the famous methane lakes and peculiar labyrinth terrains. The other two terrains are ancient hills and mountains, which are described as “hummocky”, and craters.

The map was drawn using data from the Cassini Mission and provides insight into how the moon has changed throughout its history. It is a formidable use of the mission data, combined with material from other studies, and shows how dominant these organic plains really are. Despite their prominence, the researchers still have many questions.

“There are still things we don’t understand, such as the compositional differences between the dunes (low albedo) and plains (high albedo) – does it rain more at mid-latitudes where the plains are concentrated, and not much at low latitudes where the dark dunes are?” said Dr Lopes. “We don’t have answers to many questions yet, but the map gives us an integrated, global view of the geology, which further studies of how the methane cycle operates can use.”

The map is a snapshot of Titan as it was while Cassini was studying it, but it has provided new insights into the moon’s evolution. The lack of a large number of craters tells us that the surface is constantly changing and the once abundant hummocky terrain now covers only 14 percent of the moon.

“There has been a lot of deposition of organic materials over the lifetime of Titan. The hummocky materials poke out here and there, but presumably at one time they covered most of the surface,” Dr Lopes explained. “We already knew from previous studies that there are not many craters on Titan, in fact, from this study we know they only cover 0.4 percent of the surface. So, Titan has changed substantially since its early history.”

Cassini was a joint mission of NASA, the European Space Agency, and the Italian Space Agency. The probe delivered a lander called Huygens to Titan and spent an incredible 13 years studying Saturn’s system. It collected over 450,000 images and the data was used in over 4,000 scientific papers.