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 knownmoon with a dense atmosphere and the only body, besides Earth, with stable 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. The presence of a significant amount of methane and Ar-40, the decay product of K-40, argues for exchange processes from the interior to the surface. 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 the Cassini-Huygens data. Titan is the only moon with a dense atmosphere where organic molecules are synthesized and have sedimented at the surface. The Cassini-Huygens mission demonstrated that Titan is an ocean world with an internal water shell and liquid hydrocarbon seas at the poles. Interactions between water, rock, and organics may have occurred during most of Titan's evolution, which has strong astrobiological implications. Data collected by the Dragonfly mission and comparison with the JUpiter ICy moons Explorer (JUICE) data for Ganymede will further reveal Titan's astrobiology potential.

Automated summary

The Cassini-Huygens mission revolutionized our understanding of Titan, the only known moon with a dense atmosphere and stable surface liquids, through exploration of the Saturn system from 2004 to 2017. It revealed Titan as an ocean world, with differentiation into a hydrosphere and rocky core. The presence of organic molecules synthesized and sedimented on Titan's surface, along with interactions between water, rock, and organics, have strong astrobiological implications. Further exploration by the Dragonfly mission and comparison with data from JUICE for Ganymede will reveal Titan's astrobiology potential.