Are plasma depletions in Saturn's ionosphere a signature of time-dependent water input?

Abstract

Recent radio occultation measurements by the Cassini spacecraft reveal the presence of numerous ``ionospheric holes'', or plasma depletions, in Saturn's upper atmosphere that cannot be explained with standard photochemical theory. The holes are remarkably similar in size and shape to artificially-created depletions first observed in the terrestrial ionosphere during the 1970s. At Earth, such vertical structures are typically caused by the enhanced loss of electrons and ions resulting from the introduction of spacecraft exhaust products (e.g., H₂O) into the atmosphere. Using a new model of Saturn's upper atmosphere, we show that a time-variable influx of water into Saturn's ionosphere could explain the observed plasma depletions. The required influxes present a target to assess for the possible sources and consequences of water processes throughout the Saturnian system.