Beneath Titan's ice: not an ocean, but potential local reserves of liquid water
Titan is one of Saturn's most fascinating moons. It is known for its icy surface, and it was previously thought that there was a large ocean of liquid water beneath it, similar to those hypothesised for other moons in the Solar System.
A new study published in Nature, to which Sapienza University's SPRING (Space Robotics Investigation Group) team contributed significantly, analysed data obtained from the Cassini mission, which orbited Saturn for over ten years until 2017, offering a different interpretation of Titan's internal structure.
To investigate the internal structure of the satellite, researchers studied how Titan responds to Saturn's gravitational pull, similar to how the Moon generates tides on Earth. By observing these “gravitational tides”, researchers were able to determine not only that Titan deforms significantly, but also that it responds to Saturn's gravitational pull with a delay.
This delay, which is the main focus of the research, indicates that a significant amount of energy is released in the form of heat inside the satellite.
The discovery of very high dissipation shows that Titan's interior cannot be explained by a continuous global ocean, but is more consistent with the presence of a deep layer of high-pressure, hot, partially melted ice. This result substantially changes our understanding of Titan's internal structure and demonstrates that, in order to study the interior of icy moons, it is not enough to observe deformation; it is also essential to measure how and how much energy is dissipated.
A key element that made this study possible was the integrated combination of data analysis and interior modelling, a highly interdisciplinary approach that combines expertise in aerospace engineering, geophysics and geochemistry. This type of activity represents a key line of research for Sapienza's SPRING group and was developed and applied in this work thanks to the experience of Flavio Petricca, the study's lead author, gained both at Sapienza and during his research period at the Jet Propulsion Laboratory (JPL). The consistent integration of observational data and physical models of the interior made it possible to obtain new and robust constraints on Titan's deep structure, which were not accessible with more traditional approaches. Sapienza's contribution was central to the development of an interdisciplinary approach that combines advanced analysis of space mission data and modelling of the interior of planetary bodies, a strategic area of research for the exploration of the Solar System.
‘The study,’ says Antonio Genova of Sapienza, one of the authors of the study, ‘also testifies to Sapienza's role in training researchers capable of working in international scientific contexts of excellence, such as NASA's Jet Propulsion Laboratory, and contributing directly to studies published in leading international scientific journals.’
The work provides a new criterion for interpreting tides on icy bodies in the Solar System, demonstrating that the measure of energy dissipation is key to distinguishing between liquid and solid but hot interiors. This approach can also be applied to other satellites, improving our understanding of icy worlds and their evolutionary potential.
References: Titan’s strong tidal dissipation precludes a subsurface ocean
Flavio Petricca, Steven D. Vance, Marzia Parisi, Dustin Buccino, Gael Cascioli, Julie Castillo-Rogez, Brynna G. Downey, Francis Nimmo, Gabriel Tobie, Baptiste Journaux, Andrea Magnanini, Ula Jones, Mark Panning, Amirhossein Bagheri, Antonio Genova & Jonathan I. Lunine - Nature (2025) – DOI: https://doi.org/10.1038/s41586-025-09818-x
Furthre Information
Antonio Genova - Department of Mechanical and Aerospace Engineering
T (+39) 366 6357435
Flavio Petricca – postDoc SPRING (2024); postDoc JPL (current)