Monitoring the Seasonal Evolution of the North and South Polar Vortex on Titan during 10 Years with Cassini/Vims

Tuesday, 16 December 2014: 10:35 AM
Stephane Le Mouelic1, Batiste Rousseau1, Sebastien Rodriguez2, Thomas Cornet3, Christophe Sotin4, Jason W Barnes5, Robert Hamilton Brown6, Bonnie J Buratti4, Kevin H Baines4, Roger Nelson Clark7 and Philip D Nicholson8, (1)LPGN Laboratoire de Planétologie et Géodynamique de Nantes, Nantes Cedex 03, France, (2)AIM - CEA/CNRS/Uni. P7, Gif/Yvette, France, (3)European Space Agency, Villanueva De La Can, Spain, (4)NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (5)University of Idaho, Moscow, ID, United States, (6)University of Arizona, Tucson, AZ, United States, (7)USGS, Denver, CO, United States, (8)Cornell University, Ithaca, NY, United States
Cassini entered in Saturn’s orbit in July 2004. In ten years, more than 100 targeted flybys of Titan have been performed. We focus our study on the comprehensive analysis of the Visual and Infrared Mapping Spectrometer data set acquired between 2004 and 2014, with a particular emphasis on the atmospheric polar features. First evidences for a vast ethane cloud covering the North Pole have been detected as soon as the second targeted flyby in December 2005 [1]. The first detailed imaging of this north polar feature with VIMS was obtained in December 2006, thanks to a change in inclination of the spacecraft orbit [2]. At this time, the northern lakes and seas of Titan were totally masked to the optical instruments by the haze and clouds, whereas the southern pole was well illuminated and mostly clear of haze and vast clouds. Subsequent flybys revealed that the vast north polar feature was progressively vanishing around the equinox in 2009 [2,3,4], in agreement with the predictions of Global Circulation Models [5]. It revealed progressively the underlying lakes to the ISS and VIMS instruments. First evidences of an atmospheric vortex growing over the South Pole occurred in May 2012, with a high altitude feature detected at each flybys since then. In this study, we have computed individual global maps of the north and south poles for each of the 100 targeted flybys, using VIMS wavelengths sensitive both to clouds and surface features. This allows a more complete monitoring of the evolution of the north polar cloud than was previously done before using a selection of individual flybys only. It also provides a detailed investigation of what is currently acting over the South Pole. [1] Griffith et al., Science, 2006. [2] Le Mouélic et al., PSS, 2012. [3] Rodriguez et al., Nature, 2009. [4] Rodriguez et al., Icarus 2011. [5] Rannou et al., Science 2005