Evolution of the Polar Clouds and Global Mapping of the Surface Derived From the VIMS Archive of Titan
Abstract
We have analysed of the complete Visual and Infrared Mapping Spectrometer data set of Titan covering the 2004-2017 period with two objectives: the first is to document the atmospheric seasonal changes over the poles. The second is to merge all the observations in synthetic global color maps of the surface.
For the study of the poles, we have computed individual mosaics for each of the 127 targeted flybys, using VIMS wavelengths sensitive both to clouds and surface features. These maps reveal the systematic changes that occurred in the 2004-2017 timeframe [1]. The north pole appeared fully covered by a huge cloud system as soon as the first flybys in 2004 [2]. This vast north polar feature progressively vanished around the equinox in 2009 [3, 4, 5, 6], in agreement with the predictions of Global Circulation Models [7], revealing the underlying lakes and seas. A reverse situation has been observed over the south pole, which was mostly clear of clouds and haze up to the equinox, and started to develop a giant atmospheric cloud in May 2012. This feature grew up month after month until the end of the mission in 2017, with a poleward latitudinal extent of 75°S in 2013 and up to 58°S in April 2017. Thanks to the spectral capabilities of VIMS, we have detected HCN spectral signatures over the north pole in almost all flybys between 2004 and 2008. These HCN signatures then started to show up over the south pole in almost all flybys between 2012 and 2017 [1]. For the study of the surface, we focused our efforts on data cubes acquired in the most favourable observing geometries (i.e. incidence and emergence angles lower than 80° for example). We have developed an empirical approach to mitigate the effects of the atmosphere, which otherwise induces significant seams between individual images due to the scattering and absorption of gases and aerosols. We use in particular band ratios to emphasize subtle spectral variations linked either to composition or grain size variations. Global maps at 32 pixels per degrees have been produced at specific wavelengths, revealing the surface heterogeneity of Titan. [1] Le Mouélic et al., Icarus, 311, 2018 [2] Griffith et al., Science, 310, 2006. [3] Le Mouélic et al., PSS, 60, 2012. [4] Rodriguez et al., Nature, 459, 2009. [5] Rodriguez et al., Icarus 216,2011. [6] Turtle et al., GRL, 45, 2018, [7] Rannou et al., Science 311, 2005.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P34B..05L
- Keywords:
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- 5210 Planetary atmospheres;
- clouds;
- and hazes;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 5749 Origin and evolution;
- PLANETARY SCIENCES: FLUID PLANETSDE: 6281 Titan;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS