by New research has shown the side-to-side sliding motion along the distinctive “tiger stripes” on Saturn’s moon Enceladus linked to jets of ice crystals erupting from its icy shell. The results could help determine the characteristics of this icy moon’s Saturnian subsurface ocean and, therefore, if Enceladus is favorable for life.
Enceladus’ tiger stripes are four parallel lines of fractures in the moon’s south pole first observed by NASA’s Cassini spacecraft in 2005. “Cryovolcanism” in this region destroys ice crystals believed to have come from Enceladus’ buried ocean from these fractures , causing a wide plume of material to collect over the south pole of the Saturnian moon.
The brightness of this plume and the jets that create it appear to change in a pattern that matches the nearly 33-hour orbit of Enceladus around Saturn, the second largest planet in the solar system. As a result, scientists theorize that the activity of the jets increases as tidal stress acts on the tiger stripes.
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However, this theory cannot explain why Enceladus’ jets peak in bright hours after tidal stress is at their maximum or why a second, smaller peak appears shortly after closest approach. Enceladus’s closest approach to Saturn. A new numerical simulation of Enceladus’ tidal stresses and the movement of its tiger stripe fractures identifies a phenomenon similar to that seen on the San Andreas fault, which corresponds to the pattern of jet activity.
“We developed a sophisticated numerical model to simulate the movement of tidally-driven slip along Enceladus’ faults. These models consider the role of friction, which makes the amount of slip on the faults sensitive to compressive and shear stresses,” Alexander Said Berne, the team leader behind the simulation and a PhD Candidate at the California Institute of Technology (Caltech), told Space.com.
“The numerical model was able to simulate slip along Enceladus’ faults in a way that matches observed variations in plume brightness and spatial variations in surface temperature, suggesting that the jets and plume brightness variations are controlled by orbital slip motion Enceladus. .”
The fault in San Andreas in space
Berne and her colleagues discovered that frictional mechanics governs movement at interfaces along Enceladus’ tiger stripes where the two sides of the fractures meet. This means that during Enceladus’ orbital cycle, the tiger stripes periodically slip and lock. This side-to-side motion, or “strike slip,” is consistent with jet action.
Because of the correlation between strike-slip activity and the brightness of the jets in the simulation, the team hypothesized that variations in strike-slip activity are controlled by the presence of ‘pull apart’ along the faults. These are bent sections of the fractures that open under a wide sliding motion, allowing water to rise from the subsurface ocean through the ice sheet to feed the cryovolcanic jets.
“A close earth analogy is motion along a pull-apart basin structure over large strike-slip faults subject to tectonic stresses. One example of such motion occurs over the Salton Basin – a large pull-apart located on the San Andreas fault, a strike-slip fault , in Southern California,” Berne said. “Regional strike-slip motion causes local rift extension as well as volcanism over the Balkan Basin. This process is similar to tidally driven extension along the flats at Enceladus, which may control the moon’s cryovolcanic activity.
“Before we did the research, we did not expect a high correlation between the movement of modeled slip and jet activity.”
The team’s research suggests that Enceladus’ tiger stripes open in a different way than previously modelled.
“This finding was surprising since most past studies on the subject call for a wide opening along the tiger stripes, similar to the opening and closing of an elevator door, as the main mechanism controlling the brightness variations of plumes ,” Berne said.
The Caltech researcher added that the team’s models suggest that tides play a fundamental role in the evolution of Enceladus and its oceans on different time scales.
“On the orbital time scale, tides appear to control the amount of material that flows from the subsurface ocean through the tiger stripe,” Berne said. “At longer timescales, tides may cause frictional tiger stripes to break in a purely right-lateral sense.”
He went on to suggest that this long-term right lateral motion may have driven the formation of the geological features observed around Enceladus’ south pole terrain. This includes a fracture that radiates from the South Pole on Enceladus’ follow-on Hemisphere.
Scientists have suggested that Enceladus, with its underground global ocean, could be a prime target for the search for life elsewhere in the solar system. This research and the team model could provide additional support for that hypothesis.
“Understanding subsurface material transport pathways through pull-apart zones or wide rift zones is critical to determining whether ice grains in Enceladus’ jets are representative of the Moon’s habitable global ocean. Our study provides a framework for such transport pathways. and understand their evolution over time,” Berne said.
“Evidence for the long-term influence of tides on the evolution of Enceladus, which is also heated in the interior, suggests that the moon’s ocean is long-lived, which has implications for the potential evolution of life in the interior.”
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At the moment, the team’s conclusion is based on a computer simulation and therefore needs to be confirmed with actual observations.
“Geophysical measurements at Enceladus have enabled us to confirm or refute the hypotheses outlined in our paper. More broadly, such observations of the movement of Enceladus’ surface over time can provide key constraints on the dynamics of the core and crust. as well as the extent to which these processes have been active over time,” concluded Berne. “Our aim is to continue to explore ways in which we can use geophysical measurements to better understand the conditions that could enable life on Enceladus to form and evolve.”
The team’s research was published on Monday (April 29) in the journal Nature Geoscience.
