Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis

Cassini radar observations of the surface of Ligeia Mare collected during the 23 May 2013 (T91) Cassini flyby show that it is extremely smooth, likely to be mostly methane in composition, and exhibits no surface wave activity. The radar parameters were tuned for nadir-looking geometry of liquid surfaces, using experience from Cassini's only comparable observation, of Ontario Lacus on 21 December 2008 (T49), and also include coincident radiometric observations. Radar echoes from both passes show very strong specular radar reflections and limit surface height variations to 1mm rms. The surface physical temperature at 80 degrees N is 92 +/- 0.5K if the sea is liquid hydrocarbon and the land is solid hydrocarbon, essentially the same as Cassini CIRS measurements. Furthermore, radiometry measurements over the surrounding terrain suggest dielectric constants from 2.2 to 2.4, arguing against significant surface water ice unless it is extremely porous. Key Points Ligeia Mare, like Ontario Lacus, is flat with no evidence of ocean waves or wind The sea surface dielectric constant suggests a largely methane composition Radiometric observations point to solid organic, not water ice, land surface