Titan's Complex Icy Stratosphere as Revealed by Cassini CIRS

Titan's stratospheric ice cloud structure is the most complex of any observed in the solar system. Nearly all of the trace organic vapors formed at high altitudes in Titan's thermosphere succumb to various condensation processes over a large extended altitude range in the stratosphere. This results in the formation of more than a dozen organic ice compounds - mostly nitriles and hydrocarbons - in both the pure and co-condensed states. The end result for this organic icy material is precipitation followed by deposition onto Titan's surface.

Throughout Cassini's 13-year reconnaissance of the Saturn System, the Composite InfraRed Spectrometer (CIRS) observed Titan's stratosphere to contain numerous ice clouds ranging in altitudes from just above the tropopause to the upper stratosphere. From the known stratospheric vapor abundances and predicted condensation altitudes, these clouds are expected to contain nitrile and hydrocarbon ices in both the pure and co-condensed states. To confirm the chemical identifications, subsequent transmission spectroscopy of thin ice films suggests that some of Titan's stratospheric ice clouds are chemically composed of various combinations of hydrogen cyanide (HCN), cyanoacetylene (HC₃N), benzene (C₆H₆), and dicyanoacetylene (C₄N₂). Despite the progress that has been made, a continuation of dedicated experimental efforts is needed to further unravel the formation mechanisms and chemical compositions for many of the CIRS-observed Titan stratospheric ice clouds.

In this presentation, we will review the numerous time varying spatial and chemical characteristics of Titan's CIRS-observed stratospheric ice clouds, while also detailing their most consistent chemical compositions from our ongoing experimental efforts using the SPECtroscopy of Titan-Related ice AnaLogs (SPECTRAL) chamber at NASA Goddard Space Flight Center.