Photo worth seeing: alien rivers

Photo worth seeing: alien rivers
Images from the Cassini spacecraft show rivers of methane flowing into large lakes on Saturn’s moon Titan. ©NASA/JPL/USGS

On Earth, many rivers branch into multiple branches at their mouths, forming a fan-shaped river delta—quite unlike the rivers of Titan. Liquid methane flows on Saturn’s largest moon, as shown by images from the Cassini spacecraft (NASA). This makes Titan, along with Earth and Mars, one of the only places in the solar system where there are or were rivers. But why are there so few river deltas on Titan? The curiosity of the researchers led by J. Taylor Perron and Samuel Birch from the Massachusetts Institute of Technology (MIT) was aroused.

Delta estuaries are formed when the current slows down due to the deposition of sediments carried along in the river. As early as the 2000s, Gary Parker, a geologist at the University of Illinois, developed a series of mathematical equations that describe the flow behavior of Earth’s rivers. A modified form of these results allowed the research team at MIT to predict the flow rate and amount of moved sediment in rivers based solely on river width and riverbed slope. An important step, since these two parameters can be measured in extraterrestrial fluxes using space probes.

Applying their new technique to images and elevation measurements of Mars allowed the scientists to calculate how fast rivers flowed on the red planet over a billion years ago. A comparison of the results with data from field measurements by the Mars rover Curiosity and Perseverance showed a high level of agreement.

On the Titan, the team focused on two rivers, one with and one without a delta mouth. Flow rates were found that are comparable to some of the world’s largest rivers. So both rivers should carry enough sediment to form deltas. The reason for the few deposits of the Titan rivers thus remains unknown.

Despite this unsolved mystery, the new method developed by the researchers represents an important tool for exploring extraterrestrial flow formations such as those on Mars and Titan. Birch is convinced: “Titan is the most Earth-like place and we only have a tiny impression of it get him. There is so much more that we know is there and this remote technique brings us a little bit closer.”

Recent Articles

Related Stories