Abstract

Gravity waves are low frequency fluid oscillations restored by buoyancy forces in planetary and stellar interiors, but their astrophysical importance has only been recently appreciated. In red giant stars, asteroseismically detectable gravity modes propagate into the degenerate core of the star, providing a measurement of its structure and mass. In many cases, these modes appear to be suppressed by a core magnetic field, allowing for tight constraints on internal stellar magnetism. The gravity mode spectrum can also exhibit a unique asteroseismic fingerprint of a merger event in a star’s past. In the planet Saturn, gravity modes have been detected by using its rings as a giant seismograph, revealing that the planet contains a large and diffuse core. Gravity modes can also be resonantly tidally excited in binary systems such as heartbeat stars, causing energy dissipation and tidally induced migration. A resonance locking process with tidally excited modes appears to be at work in the Saturn system, evidenced by the surprisingly rapid outward migration of its largest moon, Titan.