Saturn's upper atmosphere: auroras and 'ring rain' using new H3+ observations with Keck

Saturn's upper atmosphere is dominated by two main processes: the planetary aurora, which encircle the polar regions, and the influx of material from the rings, known as "ring rain." To observe the upper atmosphere, we measure the spectral emission lines of the major ionospheric ion H₃⁺, which are observable from Earth through key atmospheric windows using large infrared telescopes. Over the last few decades, these ion emissions have been used to determine the ion's temperature and density, mainly within the auroral region where emissions are brightest. In prior work on Saturn's aurora, we found that the southern aurora was warmer than the northern near equinox in 2011, likely due to magnetic field asymmetries, and that auroral power/density/temperature in general is modulated by Saturn's `planetary period oscillation' phenomenon. In previous work on Saturn's ring rain, we estimated the ring mass influx to the planet to be on the order of 432-2870 kg/second, which, if constant, would result in the rings demise within hundreds of millions of years. In the several years that followed these Saturn upper atmosphere results, the planets auroral and global temperature appeared to fall by approximately 100 Kelvin for presently unknown reasons, preventing our ability to probe the region, as the signal to noise ratio fell too low.

Here, we will present new results from a new observing campaign with the Keck telescope in late 2024, using the upgraded NIRSPEC instrument. Saturn’s upper atmosphere appears to have warmed again to the point that we are now able to detect H₃⁺ emission from not only the auroral region, but the mid-latitude region in which ring rain falls, allowing us to study both. This talk will discuss our new results on temperature variability in the auroral region in both hemispheres simultaneously and add a new derivation of the ring rain influx.