Re-examination of Cassini data changes understanding of Saturn's largest moon

Recent re-examination of Cassini spacecraft data has revised the understanding of Saturn’s largest moon, Titan, suggesting that it may not possess a global subsurface ocean as previously believed, according to Universe Today.

Analysis of the radio tracking and gravity data from multiple Titan flybys indicates that the interior is more likely composed of a high-pressure ice layer with pockets of partial melt, rather than a continuous liquid ocean, as reported by Nature.com.

Researchers at the Jet Propulsion Laboratory applied updated signal processing and inversion techniques to Cassini Doppler data, allowing for more precise measurements of Titan’s tidal Love numbers, Re(k2) and Im(k2), based on the findings from Universe Today and Nature.com.

New Insights into Titan’s Interior from Cassini Data

Cassini Flybys and Gravity Measurements

Cassini conducted 124 flybys of Titan between 2004 and 2017, with ten focused on measuring the moon’s gravity field to determine its internal structure, according to Nature.com.

Early analyses of tidal flexing and gravity perturbations suggested that Titan’s response to Saturn’s gravitational forces indicated a subsurface ocean, based on a high Re(k2) value measured at 0.616 ± 0.067, reported by Nature.com.

The spacecraft measured variations in speed caused by gravitational interactions, which were quantified using Doppler shifts in radio signals transmitted between Cassini and Earth, as described by Universe Today.

The new analysis recalculated Re(k2) at 0.608 ± 0.048 and provided the first direct measurement of the imaginary component Im(k2) at 0.135 ± 0.035, indicating stronger tidal dissipation than models assuming a global ocean could account for, according to Nature.com.

Interior Modeling and Tidal Dissipation

Researchers constructed interior models of Titan using a Bayesian inversion framework and a Markov chain Monte Carlo algorithm, incorporating constraints from mass, moment of inertia and both components of the tidal Love number, according to Nature.com.

These models assume a low-density rocky core, a thick hydrosphere including high-pressure ice layers, and an outer ice shell, as described by Nature.com.

Viscoelastic modeling with Andrade rheology suggests that tidal dissipation primarily occurs in the high-pressure ice layers above the core, with an average viscosity of approximately 10^12 Pa·s.

This dissipation is sufficient to allow heat to be transported outward without forming a fully liquid ocean, while the ice Ih shell convects to remove generated heat at rates consistent with observations, according to Nature.com.

Implications for Titan’s Thermal and Orbital State

The measured Im(k2) implies that Titan dissipates orbital energy at roughly four terawatts, an order of magnitude greater than radiogenic heating, according to Nature.com.

Most of this energy dissipation occurs in the high-pressure ice layer, allowing the thick outer ice shell to remain solid while transporting heat to the surface, as reported by Nature.com.

Orbital modeling indicates that Titan’s current eccentricity and outward migration may result from recent perturbations in the Saturnian system rather than primordial orbital conditions, according to Nature.com.

The tidal heating within Titan, combined with convective transfer through ice layers, prevents the formation of a global ocean while enabling pockets of partially molten ice and warm water to exist near the core, as explained by Universe Today and Nature.com.

The findings demonstrate that Titan’s hydrosphere is primarily solid, with a slushy high-pressure ice layer and potential melt pockets.

These results reconcile all available Cassini geophysical data without requiring a global subsurface ocean and suggest that Titan’s interior behaves as a highly dissipative, partially convective ice-rock system, according to Nature.com.

Upcoming missions, including Dragonfly, are expected to further test these models through direct geophysical measurements of Titan’s interior structure, according to Universe Today.

Stay tuned for more updates.