Coupling convectively driven atmospheric circulation to surface rotation: Evidence for active methane weather in the observed spin rate drift of Titan

TL;DR

This paper links Titan's observed spin rate drift to an active methane weather cycle, using models and simulations to explain the seasonal angular momentum exchange between surface and atmosphere.

Contribution

It introduces an analytic model of Titan's atmospheric angular momentum cycle and compares it with simulations, highlighting the role of methane weather in spin rate variations.

Findings

Active methane weather cycle influences Titan's rotation drift.

Seasonal cloud disappearance indicates a seasonal shift in angular momentum.

Model and simulation results align with observed spin rate changes.

Abstract

A large drift in the rotation rate of Titan observed by Cassini provided the first evidence of a subsurface ocean isolating the massive core from the icy crust. Seasonal exchange of angular momentum between the surface and atmosphere accounts for the magnitude of the effect, but observations lag the expected signal by a few years. We argue that this time lag is due to the presence of an active methane weather cycle in the atmosphere. An analytic model of the seasonal cycle of atmospheric angular momentum is developed and compared with time-dependent simulations of Titan's atmosphere with and without methane thermodynamics. The disappearance of clouds at the summer pole suggests the drift rate has already switched direction, signaling the change in season from solstice to equinox.