October 19, 2021: A New Study Suggests The Potential Presence Of Active Strike-Slip Faulting On Titan Due To Tidal Phenomena In Particular

A new research work entitled "Strike-slip faulting on Titan: Modeling tidal stresses and shear failure conditions due to pore fluid interactions", proposed by a team involving Liliane Burkhard and recently published in the journal Icarus suggests the potential presence of strike-slip faulting on Saturn's largest moon Titan due to tidal forces and due to a relatively humid crust. The crust of Titan can be relatively porous and humid in certain areas so that the crust can be relatively unstable. The researchers of the study reveal that the variations in the tidal forces from Saturn in particular during the eccentric orbit of the Opaque Moon around the Gas Giant can have a significant impact on the level of stability of Titan. Active deformation mechanisms can be envisaged. The presence of liquid methane or liquid ethane within the crust of Saturn's largest moon is likely to make it more fragile or to boost strike-slip faulting. Liquid methane or liquid ethane can infiltrate inside pores within the exotic crust. If the potential faults are found along the equatorial area with an east-west orientation, the crust can be more sensitive to tidal phenomena so that shear failure can take shape from time to time. Some fractures can be generated in the upper part of the external crust or inside the crust.

This study upon the potentially active tectonic activity of Titan was performed by a group of planetary scientists from the University of Hawai'i at Manoa School of Ocean and Earth Science and Technology (SOEST). The potential strike-slip faulting of the giant moon of Saturn can be encountered on Earth or on many other worlds in the Solar System. That's the case for Europa, a major moon of Jupiter, and that's also the case for Enceladus, a tiny moon of the Ringed Planet which appears remarkably bright. On Earth, strike-slip faulting can be observed in California, in the well-known San Andreas Fault. Several worlds located in the Outer Solar System are believed to contain oceans, seas, rivers or pockets of liquids like water, methane, ethane or ammonia beneath their external crust. That configuration may favor the presence of fractures on icy crusts. We keep in mind Europa and Enceladus which unveil fractured surfaces probably related to tidal phenomena and to a subsurface ocean rich in liquid water. Geysers have been clearly observed in the fractures of the south polar region of the icy moon Enceladus. That's a clear sign of cryovolcanism on a really small world.

The planetologists show that the tectonic movements in the phenomenon of strike-slip faulting can be closely related to the variations in diurnal tidal stresses involving the movement of the planet and the movement of its moons. The gravitation of any planetary body can engender tides on other worlds evolving in the neighborhood of that planetary body. For instance, Io, the famous moon of Jupiter, appears to be the most active moon in the Solar System. Io is extremely active in terms of volcanism due to the significant tidal forces engendered by Jupiter in particular but the other major moons of Jupiter also play a role in the tectonic activity of Io. In the system of Saturn, the numerous moons can interact, gravitationally speaking, and engender cryovolcanism. Titan can undergo the gravitational influence of moons like Tethys, Dione, Rhea or Iapetus but the major gravitational influence appears to be the influence of the Gas Giant Saturn obviously. Each world can engender a pull or a push on other worlds during its movement. In other words, the interior or the crust of any world can be shaken so that fractures can appear or develop from time to time. Our moon, The Moon, can potentially fuel our own volcanism for instance.

The crust of the Opaque Moon is believed to be relatively thick and to be dominated by water ice. In its harsh environment, water ice can be as hard as the typical rock one can encounter on our planet. The color view of the surface of Titan obtained from the Huygens probe once it had landed onto the surface on January 14, 2005 clearly shows pebbles or eroded stones which may be dominated by water ice. The Huygens probe may have landed onto an ancient brook, stream or river. In the extremely cold environment of Titan at the level of the surface, methane, ethane or propane can appear in their liquid form. The radar views as well as the infrared or near-infrared views acquired from the Cassini spacecraft during its long mission in the Saturn System from 2004 to 2017 have clearly revealed the presence of lakes, seas or rivers in the high latitudes of each hemisphere on the Orange Moon. Those stable lakes, seas or rivers can't be composed of liquid water due to the extremely low environmental temperature. Those lakes, seas or rivers turn out to be dominated by relatively light hydrocarbons or by methane or ethane. The exact composition of those liquid areas remains a subject of research today.

Titan appears to be the only extraterrestrial world in the Solar System known to contain stable seas, lakes or rivers. Saturn's largest moon demonstrates that there can be exotic seas, lakes, rivers or even oceans beyond the Earth in the Universe. Are oceans or seas dominated by methane more frequent than oceans or seas dominated by water in the Universe ? That's a relevant question ! On the basis of the relatively limited amount of information regarding the properties of the surface or the properties of the liquids found on the surface of Titan, the team of Liliane Burkhard who is a doctoral candidate and graduate student researcher in the Department of Earth Sciences at SOEST was in a position to study the potential tectonic activity of that world with the potential presence of strike-slip tectonics by mobilizing physics-based faulting models. The researchers take several parameters into account in their simulations. The phenomenon of the tidal stress, the orientations of the potential faults, the properties of the crust such as the pore fluid pressure and the stress required to engender cracks or breaking events are considered by the planetologists in their model or simulation on the potential tectonic activity of Titan.

The presence of seas, lakes or rivers on Titan is likely to make the crust less stable. Liliane Burkhard pointed out: "Titan is unique because it is the only known satellite to have stable liquids on the surface." She added: "We, therefore, were able to make an argument for integrating pore fluid pressures in our calculations, which can reduce the shear strength of the icy crust and may play a key role in the tectonic evolution of Titan." The planetologists were in a position to determine that shear failure for faults whose depth is limited is favored by the right combination of diurnal tidal stresses and pore fluid pressures. They also found that faults which are located near the equator and whose direction is roughly east-west are more likely to undergo a potential failure. Liliane Burkhard advanced: "This is an exciting revelation." She added: "Our results suggest that under these conditions, shear failure is not only possible, but may be an active deformation mechanism on the surface and in the subsurface of Titan, and could potentially serve as a pathway for subsurface liquids to rise to the surface. This can potentially facilitate material transport that could affect habitability."

The surprising dichotomy in the distribution of lakes, seas and rivers may be closely related to internal sources and to the properties of the crust. If there is a layer of liquid methane or liquid ethane beneath the external crust, the lakes, seas or rivers can be fuelled by internal sources via fractures or channels within that crust. If the crust is thinner in the polar regions of Titan, lakes, seas or rivers can develop or remain relatively stable over time. Meteorological phenomena must also play a key role in the high latitudes of the giant moon. The infrared or near-infrared views taken from the Cassini orbiter during its orbital dance in the Saturn System have clearly shown the presence of large cloud systems in the high latitudes of Titan. Those clouds which are generally composed of methane or ethane can potentially engender heavy rainfall events. We have realized that the north polar region was the most humid area on Titan during the mission of the Cassini-Huygens spacecraft in the Saturn System. During the Winter season in the northern hemisphere, the level or the size of the lakes, seas or rivers may appear higher in the high latitudes of the northern hemisphere and that would be the opposite during the Summer season in the same hemisphere.

Liliane Burkhard intends to continue her studies regarding the potential deformation of the crust of Titan. She also intends to analyze the potential deformation of other icy worlds, to deduce their tectonic history and to evaluate the potential implications of the crustal movements in terms of astrobiology. Europa and Ganymede are part of those icy worlds that may have a captivating tectonic activity. The Dwarf Planet Ceres, the moons of Jupiter, Europa and Ganymede, the moons of Saturn, Enceladus and Titan or the Dwarf Planet Pluto may contain a subsurface ocean rich in liquid water. If there are fractures within the crust, one may be in a position, in the coming years or decades, to identify interesting chemicals or molecules of that presumed subsurface ocean on the surface or on the soil of those icy worlds. Liliane Burkhard who unveiled portions of this research work, virtually, at the Europlanet Science Congress last month pointed out: "Combining new observations with our modeling techniques will strengthen our understanding of the icy crust and pinpoint the best location for exploration with a future lander mission and possibly access to the interior ocean." Very soon, we will probably gather key data regarding the dynamics or the nature of the surface of Ganymede, Europa and Titan thanks to the JUICE mission from ESA, the Clipper mission from NASA and the Dragonfly mission from NASA as well.

The image above reveals a portion of a radar swath of Titan obtained from the Cassini spacecraft during the T43 Flyby on May 12, 2008. One can notice three linear features which appear relatively parallel. Those features may be the sign of fractures of the crust. Titan is likely tectonically active. Each side of the view is about 100 km long. Credit for the original view: NASA/JPL/Cassini Radar Team/Jason Perry. Montage credit: Marc Lafferre, 2021.

- To get further information on that news, go to: https://www.soest.hawaii.edu/soestwp/announce/news/strike-slip-faulting-may-be-active-on-saturns-largest-moon-titan and https://www.sciencedirect.com/science/article/pii/S0019103521003559?dgcid=author .



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