A pole to pole pressure temperature map of Saturn's thermosphere from Cassini Grand Finale data

TL;DR

This study uses Cassini data to create a detailed pole-to-pole temperature map of Saturn's thermosphere, revealing discrepancies with models and suggesting new insights into atmospheric circulation and energy redistribution.

Contribution

It provides the first comprehensive two-dimensional thermospheric map of Saturn from pole to pole, highlighting differences from existing models and proposing mechanisms like atmospheric waves affecting energy flow.

Findings

Temperatures are cooler at auroral latitudes than predicted.

Zonal winds extend to lower latitudes than models suggest.

Evidence of atmospheric waves influencing energy redistribution.

Abstract

Temperatures of the outer planet thermospheres exceed those predicted by solar heating alone by several hundred degrees. Enough energy is deposited at auroral regions to heat the entire thermosphere, but models predict that equatorward distribution is inhibited by strong Coriolis forces and ion drag. A better understanding of auroral energy deposition and circulation are critical to solving this so-called energy crisis. Stellar occultations observed by the Ultraviolet Imaging Spectrograph instrument during the Cassini Grand Finale were designed to map the thermosphere from pole to pole. We analyze these observations, together with earlier observations from 2016 and 2017, to create a two-dimensional map of densities and temperatures in Saturns thermosphere as a function of latitude and depth. The observed temperatures at auroral latitudes are cooler and peak at higher altitudes and lower latitudes than predicted by models, leading to a shallower meridional pressure gradient. Under modified geostrophy, we infer slower westward zonal winds that extend to lower latitudes than predicted, supporting equatorward flow from approximately 70 to 30 degrees latitude in both hemispheres. We also show evidence of atmospheric waves in the data that can contribute to equatorward redistribution of energy through zonal drag.