February 18, 2025: Evaluations Of The Tidal Dissipation Rate Of Titan Bring Clues To The Dynamics Of Its Interior And To A Turbulent Past
A new research work entitled "Titan's spin state as a constraint on tidal dissipation", proposed by Brynna G. Downey and Francis Nimmo and published in Science Advances in Volume 11 and in Issue 6 on February 5, 2025 reveals an evaluation of the tidal dissipation rate of the giant moon of Saturn Titan and brings clues related to the dynamics and the nature of its interior and related to its history. Some researchers suggest the presence of a subsurface ocean rich in liquid water beneath the external crust of the Opaque Moon. The evaluations of the team of researchers suggest a relatively significant level of energy inside Titan and a relatively turbulent past. The orbit of that moon is not perfectly circular. Titan has an elliptical orbit around Saturn so that the level of tidal forces undergone by the giant moon changes over time during the long Titanian year. When Titan is closer to Saturn, it undergoes higher levels of tidal forces. When Titan is farther from Saturn, it undergoes lower levels of tidal forces related to the gravitational forces of the Gas Giant Saturn. The variations in the level of tidal forces imply an internal activity and the presence of a potential subsurface ocean beneath the external crust.
The physical and orbital characteristics of Titan clearly suggest that the moon is an active world. The value of the eccentricity of the Opaque Moon is 0.0288. Therefore, the orbit of Titan corresponds to an ellipse. The orbital period of that world is 15.945 days. In other words, it takes almost 16 days for Titan to perform a revolution around Saturn. The inclination of the orbit of Titan relative to the plane of Saturn's equator represents 0.34854 degrees. The axial tilt of Titan relative to the Sun represents 27 degrees. Over a geologic timescale, the characteristics of the orbit of Titan should evolve toward the characteristics of a circular orbit perfectly aligned with the plane of the equator of Saturn. The current characteristics of the orbit of the Orange Moon suggest that Titan has experienced significant events in its relatively recent geologic past. A strong meteorite impact can have influenced its orbital characteristics or a change in its orbital environment may have destabilized its orbit resulting in the current orbital configuration. Titan evolves in a relatively crowded environment where numerous moons can be found. Many interactions between planetary bodies can occur over a geologic timescale.
The study of the tidal forces between Saturn, Titan and the other moons such as Mimas, Tethys, Dione, Rhea or Iapetus can tell us a lot regarding the internal dynamics of the largest moon of Saturn. The presence of a significant atmosphere on Titan may be related to geysers, cryovolcanoes or active fractures that regularly fuel the atmosphere to a certain extent. In its orbit, Titan tends to progressively lose some energy due to the massive gravitational force of Saturn. Researchers try to evaluate the tidal dissipation rate to deduce the internal dynamics and the internal composition of that intriguing world. Planetologists can have a better idea upon the composition of the inner core for instance and upon the relatively recent history of the giant moon. Brynna Downey who is a Doctor and who is a postdoctoral researcher at SwRI's Solar System Science and Exploration Division in Boulder, Colorado explains in a simple way that tides are not limited to liquid motions or to the level of the sea or ocean. Tides can have an impact on the rock as well. If the level of tides undergone is strong enough, it can have an impact on the level of the soil or on the geology. It can even have an influence upon earthquakes or upon volcanic activity.
The phenomenon of tides can be extreme. The perfect example is the phenomenon of tides on Io, the most volcanically active world in the Solar System. Io is so close to Jupiter that its internal activity is extremely dynamic implying extremely active volcanoes and giant lava lakes. The value for the eccentricity of the orbit of Io is 0.0041 and the value for the inclination of its orbit is 0.036 degrees. Jupiter and the other major moons of the Gas Giant play a key role in the strong geological activity of Io. Jupiter is surrounded by four major moons. Among those four moons, Io is the nearest moon to Jupiter. Europa, Ganymede and Callisto evolve beyond Io. Europa seems particularly active thanks to tidal forces related to the other worlds of the system of Jupiter as well. Europa is a world dominated by fractures that may have a subsurface ocean rich in liquid water. Ganymede may also have a subsurface ocean rich in liquid water. Callisto that is farther from Jupiter than Ganymede may be much less dynamic at first sight. The moons of Saturn are generally rich in water ice and tend to be dominated by craters. However, the tiny moon Enceladus appears clearly active due to the presence of geysers or cryovolcanoes in particular.
In the system of Saturn, two worlds draw the whole attention of planetologists in particular. Those worlds are Enceladus and Titan. Enceladus is much closer to Saturn than Titan so that it undergoes particularly strong gravitational forces related to the Gas Giant Saturn. Tethys, Dione, Rhea, Titan and Iapetus which evolve farther from Saturn also play a role in its dynamics. The Cassini spacecraft had clearly revealed fractures in its south polar area. Those fractures unveil geysers that regularly spew water ice and other particles such as organics. Those geysers demonstrate that the internal activity of that tiny world is relatively strong with the potential presence of a subsurface ocean rich in liquid water. Another icy moon of Saturn that evolves closer to Saturn and that is smaller than Enceladus may also contain a subsurface ocean rich in liquid water. That's Mimas, a small icy world unveiling a cratered surface. Titan is more difficult to study than the other moons because it contains a completely opaque atmosphere in the visible spectrum. During its long mission in the Saturn System, the Cassini orbiter had obtained radar views and infrared or near-infrared views of its surface revealing a complex world with a diverse landscape.
The radar views obtained from the Cassini spacecraft have clearly revealed the presence of an active landscape with lakes, seas, rivers, fractures or eroded areas. Most seas, lakes and rivers tend to be found in the high latitudes of the northern hemisphere. Those lakes, seas and rivers may be dominated by a mixture of methane, ethane and dissolved nitrogen. The meteorology of Titan implies evaporation processes, condensation processes and precipitation processes. In other words, clouds can form and rainfall events can take shape on Titan like on Earth. The lakes, seas and rivers may also have internal origins with pockets of hydrocarbons, an internal network of liquid hydrocarbons beneath the surface or a layer of liquid hydrocarbons beneath the external crust. The radar views as well as the infrared and near-infrared views have allowed planetologists to identify a few candidates regarding the potential presence of active cryovolcanoes. The circular features can represent impact craters, calderas or cryovolcanoes. The atmosphere of Titan contains a haze that can engender particles that will tend to fall toward the surface so that any impact crater or caldera can be filled with those particles that form a type of mud or sludge that can appear brown, dark or orange.
The characteristics of Titan's landscape seem to be in line with the hypothesis of a relatively strong internal activity on Titan even if we haven't found any strong sign of cryovolcanism yet. The planetologists can't evaluate the tidal dissipation of Titan in the same way as we do on Earth. Researchers on our planet can measure any movement on the Moon thanks to lasers sent from Earth to mirrors installed on the Moon. That system allows us to obtain precise measurements of any movement on the Moon. We can't apply that system for Titan at the present time. Therefore, planetologists must resort to other methods in order to evaluate the tides on Titan. The researchers of the study resort to another method that consists in evaluating the difference in the spin axis rotation of the giant moon from what would be expected in the absence of tidal heating. The team of Brynna Downey has been in a position to obtain an estimate for the strength of tides on that intriguing moon. The planetologists found that the characteristics of the orbit of the giant moon are changing very quickly on a geologic timescale. They determined that the angle of the spin pole orientation can only be related to friction.
Brynna Downey and Francis Nimmo were in a position to deduce a way to relate the angle of the spin pole orientation to a tidal friction parameter. The analysis upon the current spin state allowed us to evaluate the relatively recent history of Titan. A major event must have occurred in the past 350 million years because the elliptical orbit of Titan tends to evolve toward a circular orbit over a geologic timescale. A major impact related to a big comet or a big asteroid can influence the characteristics of the orbit. The level of eccentricity of Titan can be influenced by the phenomenon. The level of inclination of the orbit of the moon can also be influenced by that type of event. Sometimes, an interplanetary body can enter a star system and modify the structure of that system due to its gravitational influence. A world like Triton may represent a captured moon of Neptune according to many planetologists. Triton may have been a dwarf planet migrating from the Kuiper Belt toward the Sun. In its path, the world may have interacted with Neptune and its moons changing the structure of the system. The Saturn System may also have undergone that type of major event in its long history since the start of the formation process of the Solar System around 4.6 billion years ago.
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The image in the upper part of the table represents a raw view of Titan and Saturn obtained from the Cassini orbiter on May 6, 2012. The image whose file name is W00074079.jpg was acquired on the basis of the CL1 filter and on the basis of the CL2 filter. The view had not been validated or calibrated at the time of the observation and a validated or calibrated version of the original image had to be archived with the Planetary Data System proposed by NASA. The view in the lower part of the table corresponds to a colorized version of the original image. Credit for the original image: NASA/JPL-Caltech/Space Science Institute. Credit for the colorization process of the original image: Marc Lafferre, 2025. |
- To get further information on that news, go to: https://www.swri.org/newsroom/press-releases/tidal-energy-measurements-help-swri-scientists-understand-titan-s-composition-orbital-history and https://www.science.org/doi/10.1126/sciadv.adl4741.