The work was based on data collected by the NASA/ESA Cassini mission to Saturn. “Our model explains the regular spacing of the cracks,” Rudolph said.
ENCELADUS TIGER STRIPES TIDAL HEATING CRACK
That causes the ice sheet to flex, the researchers calculate, just enough to set off a parallel crack about 20 miles away. But at the same time, water vented from the crack falls back as ice, building up the edges of the fissure and weighing it down a bit. The release of pressure from the fissures stops new cracks from forming elsewhere on the moon, such as at the north pole. That’s because liquid water within the fissure is sloshed around by tidal forces produced by Saturn’s gravity, releasing energy as heat, Rudolph said. Yet the south polar fissures remain open, and in fact reach all the way to the liquid ocean below. As liquid water solidifies into ice under the outer ice shell, it expands in volume, putting pressure on the ice until it cracks.Įnceladus’ surface temperature is about negative 200 degrees Celsius, so if a crack formed in the ice, you would expect it to freeze shut pretty quickly. Plotted is a polar stereographic projection of Enceladus tiger stripes and related structures south of 64uS. Saturn’s gravity exerts tidal forces on Enceladus, which cause heating and cooling of the tiny world. Figure 3 Predicted tiger-stripe stresses. Rudolph, Hemingway and Manga used numerical modeling to understand the forces acting on Enceladus’ icy shell. 9 in Nature Astronomy and will presented at the fall meeting of the American Geophysical Union in San Francisco Dec. Rudolph and colleagues Douglas Hemingway of the Carnegie Institution for Science, Washington D.C., and Michael Manga of UC Berkeley now think they have a good explanation for Enceladus’ erupting stripes.
“We want to know why the eruptions are located at the south pole as opposed to some other place on Enceladus, how these eruptions can be sustained over long periods of time and finally why these eruptions are emanating from regularly spaced cracks,” said Max Rudolph, assistant professor of earth and planetary sciences at the University of California, Davis. These fissures aren’t quite like anything else in the solar system. Slashed across Enceladus’ south pole are four straight, parallel fissures or “tiger stripes” from which water erupts. Just 300 miles across, the moon is thought to have an outer shell of ice covering a global ocean 20 miles deep, encasing a rocky core. More broadly, we hope to shed light on the conditions under which degree-one convection and a hemispheric tectonic dichotomy can occur.Saturn’s tiny, frozen moon Enceladus is a strange place. 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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