Titan occultations of Orion’s belt observed with Cassini/UVIS

Abstract

On 1 February 2016 Titan occulted the three stars in Orion’s belt, as seen from the Casssini spacecraft. The ultraviolet spectrometer on Cassini observed this event with the stars arranged along the instrument’s entrance slit. These three stellar occultations probed different latitudes in Titan’s northern hemisphere but similar longitudes. The occultations were also observed simultaneously in the extreme ultraviolet and far ultraviolet regions of the spectrum. Analysis of these measurements provides information on the atmospheric composition and thermal structure. We determine altitude profiles of N2, CH4, C2H2, C2H4, C2H6, C4H2, C6H6, HCN, and HC3N densities along with aerosol extinction. We infer significant variations in latitude for C2H2, C2H4, C4H2, aerosols, and temperature, providing clues to global circulations patterns. The inferred mole fractions of C2H2, C2H4, C4H2, C6H6, HCN, and HC3N are roughly consistent with photochemical model predictions, but C2H2 and C2H4 are over predicted by tens of percent at pressures greater than 10−5 hPa, C4H2 is under predicted by ∼ x2 at most levels, and C6H6 is under predicted by ∼ x2 at pressures less than 10−5 hPa.