Variability in Io's Volcanism on Timescales of Periodic Orbital Changes

The widespread volcanism on the Jovian moon Io is powered by tidal heating, yet we lack a deep understanding of how this distinctive heating process affects the locations, timing, or intensities of Io's eruptions. We show that the quasiperiodic behavior of the volcano Loki Patera in 1987-2018 matches the timescales for the evolution of Io's eccentricity and semimajor axis (similar to 480 and similar to 460 days). If this orbital forcing is driving Loki Patera's variability, a low-pass geophysical filter such as poroelastic flow, or a resonant amplification of Io's wobble, could account for the importance of these long-period orbital variations despite their small amplitudes. The peak volcanic response is predicted to roughly coincide with Io's maximum eccentricity, consistent with the observations. High-cadence observations over the next several years have the potential to conclusively discriminate between orbital versus geophysical control of Loki Patera's variability.