Tidal Heating at Pluto and Charon as a Result of Non-Zero Obliquity

Abstract:

The Pluto-Charon system represents a unique opportunity to examine tidal heating in a zero eccentricity system. As a result, any tidal heating in these bodies will occur as a result of finite obliquity. While Pluto and Charon’s obliquities have yet to be measured, theoretical models assuming the spin poles of the bodies are in Cassini states predict observable obliquity values.

We present a new tidal heating model for synchronously rotating bodies. As a major result of this formulation, we show how tidal heating is quadratically dependent on the h and l Love numbers, in contrast with classic models which assume homogeneous interior structure and find a linear dependence on the k Love number. Furthermore, we show how the spatial patterns of tidal heating depend on obliquity as well as eccentricity.

By applying theoretical predictions of Pluto and Charon’s spin pole orientations we examine the radially integrated spatial pattern of tidal heating at these bodies. At degree two, these patterns on Pluto predict equal heating at the sub- and anti-Charon points. Recent observations, however, show a clear dichotomy at these locations. Degree three tidal heating patterns, though reduced in magnitude, break the spatial symmetry and represent a positive indicator that tidal heating is active at Pluto and may be a source of the geologic activity at Tombaugh Regio.