Saturn's Small-Scale Winds Revealed by Its High-Degree Gravity Field

Abstract

During its Grand Finale, the Cassini spacecraft collected crucial gravity data, revealing Saturn's low-degree gravity harmonics and large-scale zonal winds extending about 8,000 km deep. However, determining the high-degree gravity field, essential for understanding small-scale atmospheric dynamics, is challenging due to the limited spatial coverage of Cassini's periapses. To overcome this limitation, we employed Slepian functions, orthogonal within a bounded domain, to represent Saturn's localized high-degree gravity field. Focusing on latitudes from 32°S to 32°N, we estimated Slepian coefficients that represent short-scale latitudinal gravity variations. The reconstructed wind profile that explains low-degree harmonics can also reproduce these high-degree variations, assuming Saturn's atmosphere is, to first order, in thermal wind balance. Our findings suggest that small-scale winds may extend to depths between 7,000 km and 9,000 km, providing strong evidence that Saturn's zonal flows are oriented along coaxial cylinders, rotating at different angular velocities.