Astrobiological implications of chaos terrains on Europa to help targeting future missions

Kereszturi, Á. and Keszthelyi, Zs. (2013) Astrobiological implications of chaos terrains on Europa to help targeting future missions. Planetary and Space Science, 77. pp. 79-90.

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Abstract

Reviewing the results from different authors on the ice crust and supposed the presence of an internal ocean inside Europa, chaos terrains and various lenticulae features might be in connection with submarine geothermal centers while pull-apart terrains and other linear features are probably in connection with tidal processes. Ranking the surface features according to the possibility how much are they connected to deep submarine processes, the above mentioned first group is more important than tidal related linear features. Surveying the size and height of blocks at the example terrain of Conamara Chaos we found that the thickness of the ice crust during its formation could be around 2 km at the rafts and 0.5 km at the matrix in agreement with some other authors’ estimated values. Calculating the hydrostatic pressure at the bottom of the about 25 km thick ice crust 10 000-20 000 kPa was estimated, and at the bottom of a 100 km deep ocean at the order of 150 000 kPa was found. At such pressure and assumed temperature, volcanic gases became solved in the water – although clathrates might also form, and could be released later as gas bubbles. This process was enhanced during the formation of chaos terrains if the ice crust thickness is only 2 km at the active phase and the pressure is around 2400-3100 kPa at its base, or inside a subsurface brine lens still roughly 100 times smaller than at the bottom of the ocean. Calthrate decomposition and bubble formation might be the most intensive at chaos regions and bubbles may be trapped between ice grains (McCord et al. 1999) or inside clathrate structure (Prieto-Ballesteros et al. 2004). Using terrestrial analog observations we conclude that trapped bubbles might be detectable remotely by the difference in the infrared and visual albedo, and by other scattering properties. The rationality of such observations is the highest at those units of the chaos regions’ low level matrix, where the smallest linear structures are present suggesting the strongest disruption, but they are not covered by debris aprons. The possibility of the detection of gas bubbles or other material floating upward in the warm rising plume is of high interest at chaos terrains, and development of detecting methods for the next Europa mission is useful.

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