Title:

Geophysical evidence for a subsurface ocean on Titan

Authors:

F. Nimmo (1), B.G. Bills (2)

Abstract:

Whether or not Titan currently possesses a subsurface ocean is crucial for understanding its long-term evolution. Here we present two lines of evidence suggesting the existence of a subsurface ocean, probably ammonia-rich.

Titan has long-wavelength topography which deviates from the expected tidally- and rotationally-distorted shape. These deviations are well- explained by a model in which ice shell thickness variations arise because of spatial variations in tidal heating. Such a model implies the existence of a subsurface ocean, and a conductive ice shell. A conductive shell implies a cold ocean, suggesting the presence of ammonia.

Titan's obliquity is larger than expected based on its measured gravity coefficients. Although it is possible that this discrepancy is due to current excitation of the obliquity (e.g. by the atmosphere), an equally plausible explanation is that Titan's shell is partially decoupled from the interior by an ocean. Future Cassini observations will be able to distinguish between these two possibilities.