Seismic Ripples Hint at Subsurface Ocean
Subtle movements on the surface of an alien world could be evidence of a life-supporting ocean. Scientists at the California Institute of Technology (Caltech) have revealed that subtle sliding motions along distinctive "tiger stripes" on Saturn's moon Enceladus could be a telltale sign of a thriving subsurface world.
The "Tiger Stripe" Enigma
The "tiger stripes" are four roughly parallel fractures near the south pole of Enceladus, first observed by NASA's Cassini spacecraft in 2005. "Ice volcanoes" in this region spew out icy crystals thought to originate from a subsurface ocean through these fractures, creating vast plumes that erupt near the south pole.
Tides Tug at Eruptions
The brightness of these plumes and the strength of individual jets within them vary throughout Enceladus' 33-hour orbit around Saturn. This led scientists to hypothesize that the jets' activity is influenced by tidal forces.
That's a welcome sign, as the presence of tides suggests that the subsurface ocean beneath the icy shell of the moon could be heated and may possess the chemical ingredients necessary to support life.
However, this theory couldn't explain why Enceladus' jets peak in brightness a few hours after tidal stresses are at their strongest or why there is a second, slightly weaker burst of eruptions shortly after Enceladus makes its closest approach to Saturn.
Tidal Stress and Fault Dynamics
Caltech's numerical simulations of Enceladus' tidal stresses and the motion of its tiger stripe fractures identified a phenomenon similar to one seen in California's San Andreas Fault. The authors found that frictional mechanics control movement in contact zones along Enceladus' tiger stripes where the two sides of the fracture come together.
Fault Slip and Jet Brightness
The correlation between lateral sliding motion and jet brightness in the simulations led the team to propose that the variation in jet flow is controlled by the presence of "dilatant zones" along the faults. These are kinked portions of the fractures that open under extensional sliding motion, allowing water from the underlying ocean to ascend through the icy crust and feed the icy plumes.
The model also suggests that this lateral sliding movement is driven by the immense tidal stresses in the subsurface.
Implications for Life
"Understanding the pathways for subsurface material transport through dilatancy zones or fractures is critical for assessing whether the icy grains within Enceladus' jets are representative of a potentially habitable global ocean," lead researcher Dr. Alexander Berne told Live Science.
The evidence for long-term tidal influence on the evolution of Enceladus, which also warms its interior, implies that the moon's ocean has been around for a substantial period. This means that life, if it exists, has had ample opportunity to take root and potentially thrive within this intriguing world.
Of course, definitive confirmation of life's presence awaits future direct exploration. NASA, which is confident that Enceladus hosts life, is developing a snake-like robot that will one day venture to the moon and plunge into its fractures in search of evidence of life within the hidden ocean.
Summary
Subtle movements on Enceladus' tiger stripes reveal evidence of tidal influence on the moon's subsurface ocean. This implies a long-lived, potentially habitable environment where life may have had ample time to evolve. Numerical simulations suggest that sliding motions along faults control the flow of icy jets that erupt from the ocean, offering a potential pathway for subsurface materials to reach the surface. This finding adds to the growing evidence that Enceladus is a prime target for future astrobiology missions.