Journal Article

Active formation of ‘chaos terrain’ over shallow subsurface water on Europa

Schmidt, B. E., Schenk, P. M., Patterson, G. W., Blankenship, D. D.

2011

Overview

The great lakes of Europa The Galileo spacecraft revealed a number of 'chaos' regions on Jupiter's moon Europa, where the surface terrain appears to have been disrupted from below. In many places, the surface contains sharp-edged blocks or rafts of ice that have at some point been flipped or rotated. Some characteristics of these regions have been hard to explain, such as the fact that the archetypal Conamara Chaos stands above its surroundings and contains matrix domes. Schmidt et al . apply lessons learned from analogous processes within Earth's subglacial volcanoes and ice shelves to an analysis of archival data that suggests chaos terrain forms above liquid water 'lenses' that are perched only 3 kilometres deep within the ice shell. The data suggest that ice–water interactions and freeze-out give rise to the varied morphology of chaos terrains, implying that more water is involved than has been previously appreciated — for instance, the sunken topography of Thera Macula, a large chaos area, may indicate that Europa is actively resurfacing over a lens comparable in volume to North America's Great Lakes. Europa, the innermost icy satellite of Jupiter, has a tortured young surface 1 , 2 , 3 , 4 and sustains a liquid water ocean 1 , 2 , 3 , 4 , 5 , 6 below an ice shell of highly debated thickness 1 , 2 , 3 , 4 , 5 , 7 , 8 , 9 , 10 . Quasi-circular areas of ice disruption called chaos terrains are unique to Europa, and both their formation and the ice-shell thickness depend on Europa's thermal state 1 , 2 , 3 , 4 , 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 . No model so far has been able to explain why features such as Conamara Chaos stand above surrounding terrain and contain matrix domes 10 , 18 . Melt-through of a thin (few-kilometre) shell 3 , 7 , 8 is thermodynamically improbable and cannot raise the ice 10 , 18 . The buoyancy of material rising as either plumes of warm, pure ice called diapirs 1 , 9 , 10 , 11 , 12 , 13 , 14 , 15 or convective cells 16 , 17 in a thick (>10 kilometres) shell is insufficient to produce the observed chaos heights, and no single plume can create matrix domes 10 , 18 . Here we report an analysis of archival data from Europa, guided by processes observed within Earth's subglacial volcanoes and ice shelves. The data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres. Our results suggest that ice–water interactions and freeze-out give rise to the diverse morphologies and topography of chaos terrains. The sunken topography of Thera Macula indicates that Europa is actively resurfacing over a lens comparable in volume to the Great Lakes in North America.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/33/445 / 704/2151/210 / Astronomy / Chaos theory / Cracks / Diapirs / Earth, ocean, space / Europa / Europa (Satellite) / Exact sciences and technology / Freshwater / Humanities and Social Sciences / Hydraulics / Ice / Ice shelves / Jupiter / Jupiter (planet) / Jupiter satellites / letter / Marine / multidisciplinary / Natural history / Observations / Planetary, asteroid, and satellite characteristics and properties / Planets, their satellites and rings. Asteroids / Science / Science (multidisciplinary) / Shells / Solar system / Subsurface water / Surface features, cratering, and topography / Terrain / Thera / Topography / Volcanoes / Water / Water, Underground