Underground ocean of water and ammonia on Saturn moon Titan

Measurements from the Cassini satellite indicate an underground ocean of water and ammonia in Saturn's moon Titan. Scientists from NASA and TU Delft have made a new analysis of precise measurements of the satellite's velocity as it flew past Titan. The speed is affected by small changes in the moon's oblateness. It was then deduced from the calculated flattening that the ocean has a lower density than previously thought and may contain a small proportion of ammonia. The antifreeze effect of ammonia may explain why the ocean is not yet frozen. The work is based partly on an internship and graduation theses by two now-graduated former Aerospace Engineering students at TU Delft. Today the research paper on the work is published in Nature Astronomy.

(Image: Representation of the Cassini satellite orbits used to calculate Titan's gravity. The coloured part of the orbits shows the distance from Cassini to Titan with the smallest distance in red. The cross-section of Titan shows the different layers of Titan with the ocean in blue. Saturn with rings and ring shadows can be seen in the background. (credits: Britt Griswold, NASA/GSFC))

Cassini space mission

The Cassini space mission flew around Saturn between 2005-2017. To precisely measure Titan's gravity, the satellite was sent close to the moon several times. The satellite had to skim past Titan at exactly the right time to properly map the change in gravity. This is because Titan's deformation is due to Saturn's tidal force, which depends on the distance between Titan and Saturn. By measuring at times when Titan is close and far away from Saturn, the difference in Titan's deformation and thus its effect on gravity was maximum. From precise radar measurements, the researchers calculated the satellite's velocity and then the change in gravity and Titan's deformation associated with it. In the new analysis, the researchers carefully examined the effect of tides on Titan at each location in the satellite's orbit and concluded that the deformation is smaller than previously calculated. Numerical simulations of the moon's deformation for different internal structures show that the most likely scenario is that the ocean has a density similar to that of water with a small proportion of ammonia.

To further map Titan's composition, it is necessary to take measurements on the moon's surface. NASA has given preliminary approval to the Dragonfly mission, which should be launched in 2027 and then arrive at Titan after 7 years and land there.