Unveiling the Mysteries of Titan’s Icy Faults: A Journey Through Space Geology

Scientists have discovered strike-slip faults on the icy moons of our solar system, similar to those seen at the San Andreas fault in California. These faults occur when fault walls slide sideways past each other. New research from the University of Hawai‘i at Mānoa, led by earth and space scientists, has explored and explained the origins of these geological features on Titan, SaturnSaturn is the sixth planet from the sun and has the second-largest mass in the Solar System. It has a much lower density than Earth but has a much greater volume. Saturn's name comes from the Roman god of wealth and agriculture.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>Saturn’s largest moon, and Ganymede, the largest moon of JupiterJupiter is the largest planet in the solar system and the fifth planet from the sun. It is a gas giant with a mass greater then all of the other planets combined. Its name comes from the Roman god Jupiter.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>Jupiter.

“We are interested in studying shear deformation on icy moons because that type of faulting can facilitate the exchange of surface and subsurface materials through shear heating processes, potentially creating environments conducive for the emergence of life,” said Liliane Burkhard, lead author of the studies and research affiliate at the Hawai‘i Institute of Geophysics and Planetology in the UH Mānoa School of Ocean and Earth Science and Technology. 

When an icy moon moves around its parent planet, the gravity of the planet can cause tidal flexing of the surface of the moon, which can drive geologic activity such as strike-slip faulting. Tidal stresses vary as the moon changes distance from its planet because the moon’s orbit can be elliptical rather than circular.

Examples of strike-slip faults on (a) San Andreas Fault (Google Maps satellite image), (b) Ganymede (Galileo SSI), (c) and Titan (Titan Cassini SAR-HiSAR Global Mosaic). Credit: (a) San Andreas Fault (Google Maps satellite image), (b) Ganymede (Galileo SSI), (c) and Titan (Titan Cassini SAR-HiSAR Global Mosaic)

Titan, a frozen ocean world

The extremely cold temperatures on the surface of Titan mean that water ice acts as rock that can crack, fault, and deform. Evidence from the CassiniThe Cassini–Huygens Mission, generally called Cassini, was a joint mission between NASA, the European Space Agency and the Italian Space Agency to study the Saturn system. Launched in 1997, Cassin provided astronomers with a massive amount of data about Saturn and its rings, its magnetosphere, and its moons. Cassini reached the end of its journey in 2017 when it deliberately dived into Saturn's atmosphere, where it disintegrated like a meteor.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>Cassini spacecraft suggests that tens of miles below the frozen surface, there is a liquid water ocean. Further, Titan is the only moon in our solar system with a dense atmosphere, which, uniquely, supports an Earth-like hydrological cycle of methane clouds, rain, and liquid flowing across the surface to fill lakes and seas, placing it among a handful of worlds that could potentially contain habitable environments. 

The NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>NASA Dragonfly mission will launch in 2027, with a planned arrival on Titan in 2034. The novel rotorcraft lander will conduct several flights on the surface, exploring a variety of locations to search for the building blocks and signs of life. 

In their investigation of the Selk crater area on Titan, the designated initial landing site for the Dragonfly mission, Burkhard and her co-author explored the potential for shear deformations and strike-slip faulting. To do this, they calculated the stress that would be exerted on Titan’s surface due to tidal forces as the moon orbits Saturn and tested the possibility of faulting by examining various characteristics of the frozen ground.

This enhanced image of the Jovian moon Ganymede was obtained by the JunoCam imager aboard NASA’s Juno spacecraft during the mission’s June 7, 2021, flyby of the icy moon. Data from that pass has been used to detect the presence of salts and organics on Ganymede. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kalleheikki Kannisto © CC BY

“While our prior research indicated that certain areas on Titan might currently undergo deformation due to tidal stresses, the Selk crater area would need to host very high pore fluid pressures and a low crustal coefficient of friction for shear failure, which seems improbable,” said Burkhard. “Consequently, it’s safe to infer that Dragonfly won’t be landing in a strike-slip ditch!”

Ganymede, a moon with a checkered past

In a second publication, Burkhard and her co-authors investigated the geologic history of Ganymede, Jupiter’s largest moon, in the area of Nippur/Philus Sulci by examining high-resolution data available for this region and conducting a tidal stress investigation of Ganymede’s past.

Ganymede has documented strike-slip faults on the surface, but its current orbit is too circular, as opposed to elliptical, to cause any tidal stress deformation. 

The researchers found that several crosscutting bands of light terrain in the Nippur/Philus Sulci site show varying degrees of tectonic deformation, and the chronology of tectonic activity implied by mapped crosscutting relationships revealed three eras of distinct geologic activity: ancient, intermediate, and youngest.  

“I investigated strike-slip faulting features in intermediate-aged terrain, and they correspond in slip direction to the predictions from modeling stresses of a higher past eccentricity. Ganymede could have undergone a period where its orbit was much more elliptical than it is today,” said Burkhard. 

Other shear features found in younger geologic units in the same region do not align in slip direction with typical first-order shear indicators. 

“This suggests that these features might have formed through another process and not necessarily due to higher tidal stresses,” Burkhard added. “So, Ganymede has had a tidal ‘mid-life crisis’, but its youngest ‘crisis’ remains enigmatic.”

The recent studies along with space exploration missions create a positive feedback of knowledge. 

“Geologic investigations, such as these, prior to launch and arrival, inform and guide mission activities,” said Burkhard. “And missions such as Dragonfly, Europa Clipper, and ESA’s JUICE will further constrain our modeling approach and can help pinpoint the most interesting locations for lander exploration and possibly for gaining access to the interior ocean of icy moons.”

References: “Exploring the initial landing site area of Dragonfly on Titan: Insights into shear failure and strike-slip faulting at Selk crater” by Liliane M.L. Burkhard and Sarah A. Fagents, 23 August 2023, Icarus.
DOI: 10.1016/j.icarus.2023.115764

“Uncovering Ganymede’s past: Tectonics at Nippur/Philus Sulci” by Liliane M.L. Burkhard, Emily S. Costello, Bridget R. Smith-Konter, Marissa E. Cameron, Geoffrey C. Collins and Robert T. Pappalardo, 2 October 2023, Icarus.
DOI: 10.1016/j.icarus.2023.115823

The study was funded by NASA Astrobiology Institute.