Long wavelength topography of Io and predicted isostatic topography resulting from spatial variation in Io's tidal heating

After deriving equations that describe the response of isostatic, long-wavelength topography to spatial variation of Io's tidal heating, we use these equations to plot this response as a function of tidal heat variation. We compare the possible range of topographic amplitude to the observed global shape of Io (after subtraction of its hydrostatic shape).

Methods
The dataset for Io limb topography used in White et al. (2014, JGR: Planets, 119(6)) has been provided courtesy of Peter Thomas. This topography is measured with respect to the reference ellipsoid of Io (Thomas et al., 1998, Icarus 135(1)).

Spherical harmonic degree 3 and 4 coefficients were generated with the method summarized in White et al. (2014), using smoothing parameter r = 3*10^7.