Latitudinal and Longitudinal Structure of Io's Atmosphere explained by an Atmosphere that is purely Sublimation Driven

Abstract

How much Io's SO2 atmosphere is driven by direct volcanic outgasing or the sublimation of SO2 surface frost is still debated. Since the sublimation supported part of the atmosphere is highly surface temperature dependent, the atmosphere is expected to have a lower SO2 column density on the nightside consistent with observations of a decreased column density in eclipse. Furthermore, the atmosphere is observed to be thicker in equatorial regions compared to the poles and when Jupiter is in Perihelion.To investigate how well observed structures of Io's SO2 distribution can be explained with a purely sublimation driven atmosphere, we developed a time dependent surface temperature model including the effect of thermal inertia. Analyzing the conductive heat transfer from Io's surface towards its interior and vice versa, which is mainly determined by the thermal diffusivity α, allows us to show that many observations can be well explained by assuming a sublimation dominated atmosphere. Simulations show that α=3.1x10-6 m2 / s yields an averaged atmospheric SO2 column density decreasing from 1016 to 2.5x1014 cm-2 from the equator to the poles. In a parameter study regarding the thermal inertia we discuss the influence of different values of the thermal inertia on the diurnal surface temperature and column density variation and find that a thermal diffusivity lower by a factor of 10 results in an atmosphere having both features, a less pronounced latitudinal dependence but a strong day-night asymmetry. Due to Io's inclination, we also find features of the surface temperature and column density that vary seasonally.