New research, led by planetary scientists from the Mānoa School of Ocean and Earth Science and Technology, University of Hawai’i, suggests that strike-slip faulting, the type of motion common along the well-known San Andreas Fault, California, Earth, possibly occurs also on Titan, Saturn’s largest moon.
On Earth, the motion along faults is driven by plate tectonics, powered by convection of the planet’s partially molten interior. As most rocky bodies in our solar system are too small to retain enough heath, tectonic movements there are very limited. Researchers believe the motion along the faults on Titan is driven by variations in diurnal tidal stresses—the push and pull caused by the relative motion of a moon and its planet.
Due to the dense atmosphere, it is not possible to directly observe Titan’s surface. In 2005, NASA’s Cassini space probe mapped Titan’s terrain thanks to RADAR and sent ESA’s Huygens lander to the surface, providing a few color images from beneath the cloud cover.
Titan has a thick crust made of rock-hard water ice. And Titan is the only place besides Earth known to have a dense atmosphere and liquids in the form of lakes and seas on its surface. However, Titan’s liquids are hydrocarbons, such as methane and ethane.
With limited observational data available, Liliane Burkhard, doctoral candidate and graduate student researcher in the Department of Earth Sciences, and co-authors of the study published in the journal Icarus, examined the possibility for strike-slip tectonics using physics-based faulting models. The model calculations take into account the tidal stress on Titan, the orientations of candidate faults, crustal properties (including pore fluid pressure), and the stress needed to cause the surface material to fail or crack.
“Titan is unique because it is the only known satellite to have stable liquids on the surface,” said Burkhard. “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 scientists found that a combination of diurnal tidal stresses and pore fluid pressures promotes shear failure for shallow faults on Titan. Further, faults near the equator that strike near east-west are optimally oriented for potential failure.
“This is an exciting revelation,” said Burkhard. “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 researchers found some direct evidence of strike-slip faulting happening now on Titan. Some river channels on Titan show an offset in their path along shear planes in a similar manner as “beheaded channels“- river channels in the desert that looked like they were once part of the original canyon before earthquakes shoved them aside – occurring along the active San Andreas Fault.
In the future, Burkhard hopes to conduct more research on the deformation of not only Titan but also other icy moons to uncover their tectonic history and astrobiological implications. The Moon Europa, orbiting Jupiter, is also believed to possess similar tectonics. It is, however, not clear whether the faults are still active.