Titan’s dunes from Cassini RADAR and VIMS observations
lead: S. Rodriguez (AIM)
coll.: O. Bourgeois - S. Le Mouélic (LPGN), A. Le Gall (LATMOS), E. Reffet (AIM)
Thousands of dunes observed on the surface of Saturn’s moon Titan are mainly confined to the equatorial belt, within ±30°, and probably cover as much as 13% of Titan’s surface (Le Gall et al., 2011). Nearly all of Titan’s dunes are linear in form (see Figure 1) and very similar in size and morphology to those found on Earth e.g. in the Namib, Chinese, Saudi Arabian deserts (Lancaster, 1995; Lorenz et al., 2006; Radebaugh et al., 2009; Lorenz and Radebauch, 2009). They are a few km wide, hundreds of km long (Lunine et al., 2008; Radebaugh et al., 2008) and tens of meters high (Barnes et al., 2008; Neish et al., 2010). Cassini Visual and Infrared Mapping Spectrometer (VIMS) and RADAR observations have shown that the composition of the sand on Titan is most probably dominated by solid organics (Soderblom et al., 2007; Barnes et al., 2008; Le Gall et al., 2011). RADAR SAR images show in particular that Titan’s dunes, similar to terrestrial linear dunes, interact with the existing topography (Radebaugh et al., 2009). The way they divert and reconnect around topographic highs provides insight into the wind regime that has sculpted them and the properties of Titan’s sand-sized sediments. However, to date, little is known on the topography of the ‘inselbergs’ or elevated obstacles embedded within Titan’s dune fields. Further, a detailed morphological study of the dunes in the vicinity of the inselbergs is lacking. Lastly, regional variations among dune fields’ properties reflect variations in the regionally available sediment supply, ground humidity, wind pattern and/or topography (Le Gall et al., 2012). Investigating the variability of dune properties will therefore provide crucial information on Titan’s climate and geological history.
Yet, numerous questions remain about the source(s) and nature of Titan’s sediment (cohesive organics?) and about the wind regimes that shaped the dunes (number, direction, strength, variability…?). Knowing with accuracy the composition, distribution, shape, orientation of the dunes will help to address these questions and constrain the carbon cycle and climate on Titan (Rannou et al., 2006; Mitchell et al., 2009; Lebonnois et al., 2009; Tokano, 2008, 2010; Rodriguez et al., 2009, 2011).
With the present task, we aimed at:
(1) Pursuing the detailed mapping of the dunes using already acquired and forthcoming SAR and VIMS images. Doing so, we will update the distribution of the dunes, refine the inventory of solid organics on Titan and facilitate the correlation of different types of data (e.g. SAR and VIMS).
(2) Investigating the topography of the dune fields and inselbergs using altimetry (Zebker et al., 2009) and SARtopo data (Stiles et al., 2009) and conducting stereo analysis of the SAR images in order to provide digital elevation models (DEMs) of all SAR overlaps that occur over dunes.
(3) Combining all Cassini RADAR (SAR, altimetry, radiometry, scatterometry) and VIMS data in order to better constrain Titan’s dune and interdune composition. The results will be analyzed in light of the GCM predictions (Rannou et al., 2006; Mitchell, 2009; Lebonnois et al., 2009).
Mapping, topographic and compositional information retrieved from RADAR and VIMS studies will be added in the planetary dunes database and will directly benefit to experimental (see WP2) and numerical (see WP3) researches. This will contribute to the thorough analysis of the role of cohesion between grains and topographic obstacles on the planetary dune morphology. Better constraints on Titan’s tropospheric circulation and near-surface winds are also expected (see Task 3.1).