Excitation Mechanisms for Jovian Seismic Modes

TL;DR

This paper investigates potential excitation mechanisms for Jovian seismic modes, finding that surface phenomena like storms are unlikely sources and proposing deep rock storms as promising candidates, with implications for future planetary missions.

Contribution

It develops an analytical model for seismic mode amplitudes driven by convective storms and explores the plausibility of various excitation sources, including deep rock storms.

Findings

Surface storms cannot account for observed amplitudes.

Deep rock storms are potential excitation sources based on energy scaling.

Constraints on Jupiter's seismic modal quality factor are estimated.

Abstract

Recent (2011) results from the Nice Observatory indicate the existence of global seismic modes on Jupiter in the frequency range between 0.7 and 1.5mHz with amplitudes of tens of cm/s. Currently, the driving force behind these modes is a mystery; the measured amplitudes are many orders of magnitude larger than anticipated based on theory analogous to heliosiesmology (that is, turbulent convection as a source of stochastic excitation). One of the most promising hypotheses is that these modes are driven by Jovian storms. This work constructs a framework to analytically model the expected equilibrium normal mode amplitudes arising from convective columns in storms. We also place rough constraints on Jupiter's seismic modal quality factor. Using this model, neither meteor strikes, turbulent convection, nor water storms can feasibly excite the order of magnitude of observed amplitudes. Next we speculate about the potential role of rock storms deeper in Jupiter's atmosphere, because the rock storms' expected energy scales make them promising candidates to be the chief source of excitation for Jovian seismic modes, based on simple scaling arguments. We also suggest some general trends in the expected partition of energy between different frequency modes. Finally we supply some commentary on potential applications to gravity, Juno, Cassini and Saturn, and future missions to Uranus and Neptune.