The Cassini mission has provided measurements of the gravity of several moons of Saturn as well as an estimate of the tidal response, which is expressed as the degree 2 Love number k₂ of its largest moon, Titan. The first estimates of Titan’s Love number were larger than pre-Cassini expectations. Interior modelling suggested it may be explained with a dense ocean, but the interpretation remains unclear. We analysed Cassini tracking data to determine Titan’s gravity field and its Love number. Our gravity results are consistent with earlier studies, but we find a lower Love number for Titan of k₂ = 0.375 ± 0.06. This lower value follows from an elaborate investigation of the tidal effects. We show that a dense ocean is not implied by the obtained Love number; instead, a water or ammonia ocean is more probable. A lower density ocean can increase the likeliness of contact between the silicate core and ocean, which can leach minerals into the ocean and could promote its habitability.

Correction to: Nature Astronomyhttps://doi.org/10.1038/s41550-024-02253-4, published online 29 April 2024 In the version of the article initially published, the affiliation of Wouter van der Wal was incorrect and has now been corrected to the Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands in the HTML and PDF versions of the article.