The northern seas on Saturn’s largest moon Titan could be experiencing seasonal phenomena similar to those found in Earth’s lakes, such as waves and bubbles, according to a study published online in Nature Geoscience. NASA’s Cassini spacecraft has been monitoring Titan since 2004, but this is its first glimpse of active surface processes in the moon’s northern hemisphere as the season slowly shifts towards summer.

Jason Hofgartner and colleagues identified bright features in Titan’s northern polar sea, Ligeia Mare, in the Cassini radar data. The bright spots were not seen in earlier or later radar images, suggesting that they are transient features. The observed features are consistent with surface waves, rising bubbles, or floating objects in or on the liquid methane sea.

Titan, with a methane cycle analogous to the Earth’s water cycle, is the only other planetary body in the Solar System with pools of stable liquid on its surface. The findings suggest that the active surface processes occurring in Titan’s seas may be an expression of the changing seasons, similarly to processes in Earth’s lakes.