Titan's middle atmosphere is currently experiencing a rapid change of season after northern spring arrived in 2009. A large cloud was observed for the first time above Titan's southern pole in May 2012, at an altitude of 300 km. This altitude previously showed a temperature maximum and condensation was not expected for any of Titan's atmospheric gases. Here we show that this cloud is composed of micron-sized hydrogen cyanide (HCN) ice particles. The presence of HCN particles at this altitude, together with new temperature determinations from mid-infrared observations, indicate a very dramatic cooling of Titan's atmosphere inside the winter polar vortex in early 2012. Such a cooling is completely contrary to previously measured high-altitude warming in the polar vortex, and temperatures are a hundred degrees colder than predicted by circulation models. Besides elucidating the nature of Titan's mysterious polar cloud, these results thus show that post-equinox cooling at the winter pole is much more efficient than previously thought.
@article{arxiv.1410.5563,
title = {HCN ice in Titan's high-altitude southern polar cloud},
author = {Remco J. de Kok and Nicholas A. Teanby and Luca Maltagliati and Patrick G. J. Irwin and Sandrine Vinatier},
journal= {arXiv preprint arXiv:1410.5563},
year = {2015}
}
Comments
Published in Nature on 2 October 2014. This is the author version, before final editing by Nature