Detection and characterization of Io’s atmosphere from high-resolution 4-µm spectroscopy E. Lellouch1, M. Ali-Dib1,2, K.-L. Jessup3, A. Smette4, H.-U. Käufl4, and F. Marchis5 1Laboratoire d’Études Spatiales et d’Instrumentation en Astrophysique (LESIA), Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, F-92195 Meudon, France ;
[email protected] 2Institut UTINAM, CNRS/INSU, Université de Franche-Comté, UMR 6213, Observatoire de Besançon, BP 1615, F-25010, Besançon Cedex, France 3 Dept. Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, United States 4European Southern Observatory (ESO), Karl-Schwarzschildst. 2, D-85748 Garching, Germany 5SETI Institute, 189 Bernardo Av, Mountain View CA, USA. Icarus, in press. Abstract We report on high-resolution and spatially-resolved spectra of Io in the 4.0 µm region, recorded with the VLT/CRIRES instrument in 2008 and 2010, which provide the first detection of the 1+3 band of SO2 in Io’s atmosphere. Data are analyzed to constrain the latitudinal, longitudinal, and diurnal distribution of Io’s SO2 atmosphere as well as its characteristic temperature. equatorial SO2 column densities clearly show longitudinal 17 -2 asymmetry, but with a maximum of ~1.5x10 cm at central meridian longitude L = 200-220 16 -2 and a minimum of ~3x10 cm at L = 285-300, the longitudinal pattern somewhat differs from earlier inferences from Ly α and thermal IR measurements. Within the accuracy of the measurements, no evolution of the atmospheric density from mid-2008 to mid-2010 can be distinguished. The decrease of the SO2 column density towards high latitude is apparent, and the typical latitudinal extent of the atmosphere found to be ±40° at half-maximum.