Post by Rosaly Lopes,  Randy Kirk,  and Mary Bourke,

Jet Propulsion Laboratory, California Institute of Technology, California, USA.

US Geological Survey, Astrogeology Science Center, Flagstaff, Arizona, USA.

Geography, Trinity College, Dublin, Ireland.

Data from the Cassini mission have revealed that Titan is a planetary body where the interior, the surface, and atmospheric processes interact to create and modify landforms (Loppes et al, 2010). In terms of recent surface processes, Titan is one of the most earth-like bodies in our solar system. Landforms include the largest area of aeolian dunefields in our solar system (e.g., Radebaugh et al., 2008), lakes (e.g., Stofan et al., 2006), fluvial channels (e.g., Langhans et al., 2012), mountains (e.g., Radebaugh et al., 2007), and features that have been interpreted as volcanic (e.g., Lopes et al., 2007).

Image 1: The RADAR (SAR) images in black and white over a false-color mosaic of VIMS data. The globe at upper left shows the location of the map on Titan (arrow). The white lines show the approximate boundaries of the perspective view in Image 2.

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Post by Dr Catherine Neish

Cryovolcanism (or ‘cold’ volcanism) describes the eruption of substances that are generally considered to be volatiles on the surface of Earth (eg. water, water-ammonia mixtures, etc.). Cryovolcanism is functionally similar to the volcanism we see on Earth, except that cryolavas (‘cold’ lavas, such as water) erupt at much lower temperatures than rock lavas. As with all forms of volcanism, two conditions must be met for cryovolcanic flows to be present on the surface of an icy moon: liquids must be present in the interior, and those liquids must then migrate to the surface. The latter requirement is more difficult to achieve for cryolavas than rock lavas, given that solid ice is less dense than water. The addition of some amount of ammonia can reduce the density difference – a liquid ammonia-water mixture of peritectic composition (33 wt. % ammonia, 946 kg m³) is near neutral buoyancy in ice (917 kg m³). Though these pockets would not easily become buoyant on their own (given the difference in density of ~20-30 kg m³), they are sufficiently close to the neutral buoyancy point that large-scale tectonic stress patterns (tides, non-synchronous rotation, satellite volume changes, solid state convection, or subsurface pressure gradients associated with topography) could enable the lavas to erupt effusively onto the surface.

Image 1: A portion of the RADAR swath taken during the Cassini spacecraft’s TA (Titan-A) encounter on October 26, 2004 (Elachi et al. 2005). This image shows several possible cryovolcanic features, including overlapping flow features (right) and the large circular feature Ganesa Macula (left). Radar illumination is from the bottom.

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