Azimuthal temperature modulations of Saturn’s A ring caused by self-gravity wakes

• We develop a new model for thermal emission of Saturn’s rings.
• Wakes are modeled as elliptical cylinders ignoring inter-wake particles.
• The thermal inertia of the A ring wakes is estimated to be 10 J m−2 K−1 s −1/2.
• The bolometric reflectance of the wake surface is 0.35–0.4.

The physical temperatures of the Saturn’s A ring measured by the Cassini Composite Infrared Spectrometer (CIRS) show quadrupole azimuthal modulations besides temperature drops in Saturn’s shadow. These azimuthal modulations are likely to be caused by self-gravity wakes. In this paper, we develop a new thermal model in which wakes are modeled as elliptical cylinders ignoring inter-wake particles. All the heat fluxes are calculated explicitly taking into account inter-wake shadowing and heating. We apply our model to azimuthal scans of the A ring obtained by CIRS. It is found that the azimuthal modulation of the ring temperature is primarily caused by the azimuthal variation of the geometric filling factor of the ring seen from the Sun. The thermal inertia estimated from the eclipse data (data only inside and near Saturn’s shadow) of the low phase scans is ∼10 J m−2 K−1 s−1/2. With this value of the thermal inertia, the amplitude of the azimuthal temperature modulation is overestimated in our model as compared with those observed. This is likely to be because our model ignores inter-wake particles. The bolometric reflectance of wakes is estimated to be 0.35–0.40 although lower values are required to reproduce temperatures at low solar phase angles. This apparent phase dependence of the reflectance indicates that roughness on the wake surfaces is necessary.