Titan: Atmospheric and surface features as observed with Nasmyth Adaptive Optics System Near-Infrared Imager and Spectrograph at the time of the Huygens mission

At the time of the Huygens probe descent in Titan's atmosphere, on 14 January 2005, many ground-based telescopes were pointed toward Saturn's satellite. Here, we describe the data collected on 15 and 16 January with Nasmyth Adaptive Optics System Near-Infrared Imager and Spectrograph (NACO) at the Very Large Telescope. We acquired adaptive optics images in the near-infrared in several NACO modes, 18 then 41 hours after Huygens landing. A variety of different filters, a cryogenic tunable Fabry-Perot interferometer, and a simultaneous differential imager were used. All these data allowed us to construct a diagnostic of the appearance of Titan's atmosphere and surface at the time of the Huygens probe's descent. We describe the north-south and east-west asymmetries characterizing the atmosphere, while reporting on more active phenomena, like cloud activity. The surface of Titan around the Huygens probe's landing site is imaged with a 320-km spatial resolution, through three methane windows at 1.28, 1.6, and 2.0 μm; it shows features similar to those previously published in near-infrared maps, with a spectral behavior compatible with methane and water ices