From the May 2018 issue

Does Titan experience any tides in its oceans, or is it tidally locked with no tides?

Richard Robinson Clay, New York
By | Published: May 31, 2018
Titan’s orbit is slightly elliptical, bringing it closer to Saturn during some points and taking it farther during others. The moon is most spherical at the farthest point from the planet, and most football-shaped when it passes closest to Saturn; the amount of deformation Titan experiences requires a liquid ocean beneath its surface.
In 2012, Cassini revealed that, based on data taken between 2006 and 2011, Saturn’s largest moon, Titan, changes shape due to tides raised on the satellite as it circles the planet. Over the course of its nearly 16-day orbit, Titan’s surface deforms by more than 33 feet (10 meters).

This amount of tidal deformation is associated with a malleable, likely liquid ocean layer inside the moon. Current estimates place Titan’s ocean at more than 62 miles (100 km) thick. If Titan were solid all the way through, the expected deformation of the surface throughout its orbit would total only about 3 feet (1 m).

However, like most of the solar system’s larger satellites, Titan is tidally locked to Saturn. A tidally locked satellite simply rotates once per every orbit around its parent body, always showing the same face to the planet. Such satellites can still experience tides. Because Titan’s orbit is elliptical, the gravitational influence of Saturn from the near to far side of the moon varies throughout its orbit, which causes the deformations recorded by Cassini.

Alison Klesman 
Associate Editor