Saturn’s small-scale winds revealed by its high-degree gravity field

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