Cassini CIRS update on stratospheric ices at Titan's winter pole

Abstract

A strong, broad spectral emission feature at 85° N latitude centered at 221 cm ^-1 remains unidentified after candidate ices of H ₂O and pure crystalline CH ₃CH ₂CN are unambiguously ruled out. A much shallower weak emission feature starts at 160 cm ^-1 and blends into the strong feature at ∼190 cm ^-1. This feature is consistent with one formed by an HCN ice cloud composed of ⩽5 μm radius particles that resides in the lower stratosphere somewhere below an altitude of 160 km. Titan's stratospheric aerosol appears to have a spectral emission feature at about 148 cm ^-1. The aerosol abundance at 85° N is about a factor 2.2 greater than at 55° S.