The recent study also found that it’s more difficult to form fractures through the entire ice shell than previously thought. “The ocean is under pressure, so water is forced into tiny cracks at the base of the ice shell, which widens and propagates the cracks all the way up to the surface,” says Carolyn Porco, a planetary scientist and visiting scholar at the University of California, Berkeley, and former leader of the Cassini Imaging Team, who suggested this possibility with colleagues in 2014. But fractures that begin at the base of the ice shell have a better chance of piercing the surface, especially if they connect with cracks that originate from the top of the ice shell. This new research shows that fractures originating at the surface are unlikely to reach the subsurface ocean, even for thinner ice depths. “Our models show that tidal stresses can fracture the ice shell all the way through, but indirectly limit how thick the ice can be,” says Catherine Walker, a glaciologist from the Woods Hole Oceanographic Institution and lead author of a recent study published in The Planetary Science Journal. To understand exactly how the tiger stripes formed, researchers model ice shell fractures based on various thicknesses. These famous features are surrounded by 300-meter-high margins that form a valley-like trough up to several kilometers wide at the moon’s surface. Enceladus’ tiger stripes are unusual because they extend down to the ocean - and they present an enticing opportunity to search for evidence of life outside Earth. Tidal stresses can crack the ice shell, but it may be difficult for these fractures to travel all the way through. Scientists think that these tidal stresses generate enough heat to sustain the liquid water. These form when gravity from the planet they orbit stretches and squeezes their interior. For example, Jupiter has several of them. Icy moons that have (or are thought to have) subsurface oceans are common in the outer solar system. Some of the ice even escapes the moon’s gravity and forms Saturn’s E-ring. At the moon’s south pole, the subsurface ocean erupts from one hundred geysers located along four parallel fractures known as ‘tiger stripes.’ The towering jets of ice particles form a plume that snows back down to the surface. More broadly, we hope to shed light on the conditions under which degree-one convection and a hemispheric tectonic dichotomy can occur.Enceladus, Saturn’s sixth largest moon, is awash with liquid water beneath its icy shell. We determine the conditions under which convection can produce regional tectonic deformation patterns resembling the south polar terrains. The temperature structure and heat flux are calculated and compared with relevant observational constraints. Temperature-dependent viscosity, pseudo-plasticity, tidal heating, and enhanced shear heating along the tiger stripes are implemented in the simulations. We perform our simulations using the finite element codes ConMan in 2D Cartesian and CitcomS in 3D spherical geometries. We present numerical simulations of thermal convection in Enceladus' ice shell to understand the formation of the south polar tectonics. However, these models did not represent brittle deformation near the surface of the ice shell and shear heating along the tiger stripes in a realistic way. Several groups have shown that convection may occur in Enceladus' interior. It has been suggested that the source for Enceladus' tectonic activity is convection/diapirism in the ice shell coupled with tidal dissipation. The surface temperature and heat flux are strongly elevated along the tiger stripes. Enceladus' south polar region exhibits a diversity of heavily tectonized terrains, including a complex assortment of ridges, grooves, graben, and rifts.
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