Dissipation of tidal energy in synchronously rotating satellites and super-Earths

Most natural satellites and close-in rocky exoplanets are locked in synchronous rotation and subject to tidal forces exerted by their primaries. It is generally believed that the triaxial ellipsoidal shape of their surfaces was acquired in a tidal environment early after formation, when the deep interiors were sufficiently hot and deformable and overlain by thin lithospheres. The nonspherical part of the corresponding low-degree gravity fields is also predominated by spin and tidal contributions, which are related to the radial mass distribution. In addition, time-varying surface distortion and gravity variation due to tiny radial and librational tides may occur along slightly non-circular orbits, thereby causing the dissipation of tidal energy by internal friction. This has important consequences for the orbital evolution and present thermal state of planetary satellites and close-in exoplanets. Here, we examine the possible role of tidal dissipation in regards to internal heat transfer, partial melting, core composition and state (solid vs. liquid), and implications for magnetic field generation.