Geophysical implications of the long-wavelength topography of Rhea

Abstract

We use limb profiles to investigate the long-wavelength topography and topographic variance spectrum of Rhea. One-dimensional variance spectra show a break in slope at a wavelength of ≈300 km; a similar effect is seen on the Moon and may be a signature of an elastic lithosphere having a thickness T_e ≈ 10 km. The implied heat flux is ∼15 mW m^-2, much higher than can be explained by radiogenic heating. We use the 1-D spectral behavior to constrain our solution for the long-wavelength global topography of Rhea. The degree 3 topography is large enough, if uncompensated, to contaminate estimates of the degree 2 gravity using existing flyby data. Current models of Rhea internal structures which rely on these degree 2 estimates may thus be inaccurate, illustrating the need to acquire further Rhea gravity data.