Titan’s Gravity: An Update

Since its arrival at Saturn in 2004, Cassini performed nine flybys devoted to the determination of Titan’s gravity field and its tidal variations. The last gravity flyby of the mission (T122) took place on Aug. 10, 2016. We will present an updated gravity solution, based on all available data. These include also an additional flyby (T110, March 2015, primarily devoted to the imaging Titan’s north polar lakes) carried out with the low gain antenna. This flyby was particularly valuable because closest approach occurred at high latitude (75oN), over an area not previously sampled. Published gravity results (Iess et al., 2012) indicated that Titan is subject to large eccentricity tides in response to Saturn’s time varying forcing field. The magnitude of the response quadrupole field, controlled by the Love number k2, was used to infer the existence of an internal ocean. The new gravity field determination provides a better estimate of k2, to a level of a few percent. In addition to a full 3x3 field, the new solution includes also higher degree and order harmonic coefficients (such as J4) and offers an improved map of gravity anomalies. The updated geoid and its associated uncertainty could be used to refine the gravity-altimetry correlative analysis and for improved interpretation of radar altimetric data.