Particle size and abundance of HC3N ice in Titan's lower stratosphere at high northern latitudes

Up to now, there has been no corroboration from Cassini CIRS of the Voyager IRIS-discovery of cyanoacetylene (HC3N) ice in Titan's thermal infrared spectrum. We report the first compelling spectral evidence from CIRS for the v(6) HC3N ice feature at 506 cm(-1) at latitudes 62 degrees N and 70 degrees N, from which we derive particle sizes and column abundances in Titan's lower stratosphere. We find mean particle radii of 3.0 mu m and 2.3 mu m for condensed HC3N at 62 degrees N and 70 degrees N, respectively, and corresponding ice phase molecular column abundances in the range 1-10 x 10(16) mol cm(-2). Only upper limits for cloud abundances can be established at latitudes of 85 degrees N, 55 degrees N, 30 degrees N, 10 degrees N, and 15 degrees S. Under the assumption that cloud tops coincide with the uppermost levels at which HC3N vapor saturates, we infer geometric thicknesses for the clouds equivalent to 10-20 km or so, with tops at 165 km and 150 km at 70 degrees N and 62 degrees N, respectively. Published by Elsevier Inc.