Imagine a world where mountains are made of rock-solid ice and lakes are full of liquid methane. Sound like a science fiction movie set? In fact, this is a true description of Titan, Saturn’s largest moon. Jani Radebaugh, a faculty member in the Department of Geological Sciences, has dedicated a large portion of her professional career to understanding this heavenly body and the insights it may provide into Earth’s own natural processes.
Titan has received special attention because its atmosphere and surface remarkably resemble that of Earth. Unlike any other known planet, Titan’s atmosphere contains large amounts of nitrogen, as well as carbon and hydrogen, organized into organic molecules. While the presence of these substances does not indicate there is life on Titan, the body may be a good place to look for life or prebiotic processes. In addition, Titan experiences rain fall and river flow, with methane as the liquid. Because it is the only other known body that sustains such complicated weather systems, Titan has become an important analog to Earth’s processes.
Having another world with similar processes is especially convenient when studying the formation of sand dunes, an activity that helps researchers to better understand climate and atmospheric processes – both on Earth and on other heavenly bodies. While it is certain that wind plays a key role in the dunes’ creation, it is less evident how this element works with the sand to create large mounds and snake-like patterns. Titan’s sand dunes have become a particular source of intrigue for Radebaugh.
“I would like to understand what processes have made these features that are so similar to Earth’s, yet made up of such different materials,” she explained.
Titan provides certain advantages when trying to solve the riddle of sand dunes. First, it has a larger area of dunes to study. While only 5 percent of Earth’s surface is made up of sand dunes, 20 percent of Titan is covered with fine particles of organic material, similar in texture, color, and even chemical makeup to coffee grounds and comparable in size and behavior to sand found on Earth.
The material on Titan also moves more freely because there are no plants anchoring it. Moreover, because Titan’s methane oceans are located in its polar regions, fine particles can blow across most of the planet without getting stuck in or obstructed by large bodies of liquid, as is the case on the ocean-planet Earth. With many interfering factors eliminated on Titan, it is easier to identify the impact that wind patterns have on creating sand dunes.
There are several theories about how linear dunes, the type found on Titan and in Earth’s largest deserts, are formed. The currently favored model states that opposing, or obliquely angled, winds combine to produce these linear dunes stretched out along the average wind direction. Determining if this model is correct is important because it will allow researchers, like Dr. Radebaugh, to better understand the winds on Titan. Applying this model to Titan suggests that the dominant winds there move from east to west, but it also requires there to be several, perhaps seasonal, wind directions.
Radebaugh’s expertise on Titan’s dunes has attracted professional attention. The prestigious journal Nature Geoscience recently solicited Radebaugh’s educated opinion on a paper by Dave Rubin proposing an alternate theory of how dunes may be formed on Titan.
While studying the dunes of China, Rubin noticed that some were sticky. Instead of dry, fine particles of sand–the material most dunes are composed of–these dunes are formed from bits of clay. When the wind blows, these sticky clay clumps roll along the ridge and attach to the downwind margin, lengthening the dunes in the downwind direction. He suggested that Titan’s dunes may possess similar, sticky qualities, and therefore require winds from only one direction.
In her response paper, Radebaugh cautiously noted that one theory may not apply to every situation. However, she optimistically accepted Rubin’s theory as viable. This new idea may be another piece to the puzzle of Titan’s dunes and serve as a step closer to understanding Earth’s functions as well. By comparing Titan and Earth, Radebaugh may make substantial progress in reaching her goal.
“I am trying to answer, what are these basic landforms on Earth and other planets, and what processes created them?” she said.