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 μ m; it shows features similar to those previously published in near‐infrared maps, with a spectral behavior compatible with methane and water ices.