Scientists have discovered slip faults similar to California's San Andreas fault, which occur when fault walls slide against each other, on the solar system's icy moons. New research from the University of Hawai'ia at Mānoa, led by Earth and space scientists, explores and explains the origin of these geological features on Saturn's largest moon Titan and Jupiter's largest moon Ganymede.
"We are interested in studying shear deformation on icy moons because this type of faulting can facilitate the exchange of surface and subsurface material through shear heating processes, potentially creating an environment conducive to the emergence of life," said Liliane Burkhard, lead author of the study and a researcher at the Hawaii Institute of Geophysics and Planetology in the College of Ocean and Earth Science and Technology at the University of Hawaii at Manoa.
As the icy moon orbits its parent planet, the planet's gravity causes tidal flexing of the moon's surface, triggering geological activity such as sliding faults. Because the Moon's orbit is likely to be elliptical rather than circular, tidal stresses vary as the Moon's distance from its planet changes.
Titan, a frozen ocean world
The extremely cold temperatures on Titan's surface mean that water ice, like rock, can crack, fault and deform. The Cassini spacecraft has provided evidence that there is an ocean of liquid water dozens of miles beneath the frozen surface. In addition, Titan is the only moon in the solar system with a dense atmosphere, which is unique in that it supports an Earth-like hydrological cycle, in which methane clouds, rainfall, and liquids flow across the surface to form lakes and oceans, making it one of the few worlds that may contain a habitable environment.
NASA's Dragonfly mission will launch in 2027 and is scheduled to arrive at Titan in 2034. The novel rotary-wing lander will make several flights across Titan's surface, exploring various locations in search of building blocks and signs of life.
In their investigation of the Selke Crater region on Titan, the designated initial landing site for the Dragonfly mission, Burkhard and her co-authors explored the possibility of shear deformation and strike-slip faulting. To do this, they calculated the stresses exerted on Titan's surface by tidal forces as it orbits Saturn, and tested the possibility of faulting by studying various features of the frozen ground.
"While our previous studies have shown that some areas on Titan may currently be deformed by tidal stress," Burkhard said, "the Selke crater region would need to withstand very high pore fluid pressures and low crustal friction coefficients for shear failure to occur, and this does not appear to be possible. So, it is a safe bet that the dragonfly will not land in a trench that is sliding!"
Ganymede, a moon with a checkered past
In the second paper, Burkhard and her co-authors examined the geological history of the region by studying high-resolution data from the Nippur/Pheleus-Sulsi region of Jupiter's largest moon, Ganymede, and conducting tidal stress investigations into Ganymede's past.
Ganymede has records of strike-slip faults on its surface, but its current orbit is too rounded rather than elliptical to cause any tidal stress deformation.
The researchers found that several light terrain cross-cutting zones at the Nippur/Pheles-Sulsi site showed varying degrees of tectonic deformation, and the chronology of tectonic activity implied by the drawn cross-cutting relationships showed three different eras of geological activity: the Ancient Era, the Medieval Era and the Youngest Era.
"I investigated strike-slip fault signatures in the Mesozoic terrain, and they slid in directions consistent with modeling stress predictions of higher eccentricities in the past," Burkhard said. "Ganymede may have experienced a period when its orbit was much more elliptical than it is today."
Other shear features found in younger geological units in the same area are not consistent in slip direction with typical first-order shear indicators.
"This suggests that these features may have formed through another process, not necessarily due to higher tidal stress," Burkhard added. "Thus, Ganymede experienced a tidal 'midlife crisis,' but its youngest 'crisis' remains a mystery."
Recent research and space exploration missions create a positive feedback loop of knowledge.
Burkhard said geological surveys conducted before launch and arrival provided information and guidance for mission activities. Missions such as Dragonfly, Europa and ESA's JUICE will further constrain our modeling approach and help identify locations of greatest interest for landers to explore and potentially access the inner oceans of icy moons.
Compiled source: ScitechDaily