Titan's Interior structure and dynamics after the Cassini/Huygens mission

The Cassini-Huygens mission that explored the Saturn system during the period 2004-2017, revolutionized our understanding of Titan, the only known moon with a dense atmosphere and the only body, besides Earth, with surface liquids. Its predominantly nitrogen atmosphere also contains a few percent of methane that is photolyzed on short geological timescales to form ethane and more complex organic molecules, and 40Ar, the decay product of 40K. The presence of these two compounds argue for the interior-surface exchange processes. Here we review the information that constrains Titan’s interior structure. Gravity and orbital data suggest that Titan is an ocean world, which implies differentiation into a hydrosphere and a rocky core. The mass and gravity data complemented by equations of state constrain the ocean density and composition as well as the hydrosphere thickness. We present end-member models, review the dynamics of each layer, and discuss the global evolution consistent with orbital data.