Figure 1: Image of Titan taken by NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/Space Science Institute.
Both Sionascaig Lacus and Urmia Lacus have lacustrine (i.e. associated with lakes) morphologies. For example, the surface of a lake is usually darker than its surrounding terrain. This is seen for both Sionascaig Lacus and Urmia Lacus, whereby the light-dark boundary outlining each potential lake is continuous, and appears quite similar to previously confirmed lakes on Titan, such as Ontario Lacus.
At the cold cryogenic temperatures on Titan, the seas and lakes on Titan are comprised of liquid hydrocarbons, mainly methane and ethane. When observed in the infrared, the surfaces of these seas and lakes have very low albedos (i.e. they appear very dark) because methane and ethane are strong absorbers in the 5 μm waveband. Sionascaig Lacus and Urmia Lacus are consistent with being bodies of liquid hydrocarbons due to their very low albedos. The surface albedos of Sionascaig Lacus and Urmia Lacus are 0.0070 and 0.0081, respectively. For comparison, the surface albedos of Kraken Mare and Ligeia Mare, two large northern seas on Titan, are 0.0114 and 0.0050 to 0.0089, respectively.
Figure 2: Artist’s impression of a lake on Titan.
The terrain surrounding Sionascaig Lacus and Urmia Lacus also exhibit low surface albedos, albeit not as low as the surfaces of the two potential lakes. It appears that the surrounding terrain could be interpreted as a wetland, with the ground soaked in liquid hydrocarbons. Sionascaig Lacus is by far the larger of the two potential lakes. Its surface area is estimated to be ~5000 km² and its average depth is estimated to be around 40 to 70 m. Sionascaig Lacus is also estimated to hold roughly 100 billion tons of liquid methane. Clouds have been observed on Titan’s southern mid-latitudes. The presence of temperate lakes may be driving cloud formation or be the result of cloud activity (i.e. precipitation); most likely both.
G. Vixie et al. (2015), “Possible temperate lakes on Titan”, Icarus Volume 257, 1 September 2015, Pages 313 to 323