NASA Scientists –“Vast Ocean of Saturn’s Moon Enceladus Could Be the Site of a Second Genesis”

 

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Chris McKay, an astrobiologist with NASA  says: “I’ve been interested in the search for life in the Solar System for decades and I’m still flabbergasted by what we’re seeing on Enceladus. It’s such a small world so far from Earth, putting out such a wealth of organics and water and indications of habitability – it’s astounding, and the samples are right there, free for the taking.”


With enormous jets of icy particles and water vapor shooting tens of thousands of kilometers into space, and an vast, global ocean covered by an ice shell, Saturn’s moon Enceladus is one of the most fascinating objects in our Solar System. NASA’s Carolyn Porco, director of flight operations and imaging team leader for the Cassini spacecraft in orbit around Saturn, has described findings of the jets and elevated temperatures at the moon’s South Pole as “the mother lode of all discoveries.” The findings, noted Porco, point to the possibility of “an environment where life itself might be stirring.”

 

Complex organic molecules, whose precise composition remains unknown, have been detected in Enceladus’s jets, creating conditions appear to be favorable to the emergence of life. The relative thinness of the ice shell at the south pole could also allow a future space exploration mission to gather data, in particular using radar, which would be far more reliable and easy to obtain than with the 40 kilometers thick ice shell initially calculated. It looks as if Enceladus still has many secrets in store!

“Should we ever discover that a second genesis had occurred in our solar system, independently outside the Earth,” Porco added, “then I think at that point the spell is broken. The existence theorem has been proven, and we could safely infer from it that life was not a bug but a feature of the universe in which we live, that it’s commonplace and has occurred a staggering number of times.”

 

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An international team including researchers recently proposed a new model that reconciles different data sets and shows that the ice shell at Enceladus’s south pole may be only a few kilometers thick. This suggests that there is a strong heat source in the interior of Enceladus, an additional factor supporting the possible emergence of life in its ocean.

 

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Initial interpretations of data from Cassini flybys of Enceladus estimated that the thickness of its ice shell ranged from 30 to 40 km at the south pole to 60 km at the equator. These models were unable to settle the question of whether or not its ocean extended beneath the entire ice shell.

However, the discovery in 2015 of an oscillation in Enceladus’s rotation known as a libration, which is linked to tidal effects, suggests that it has a global ocean and a much thinner ice shell than predicted, with a mean thickness of around 20 km. Nonetheless, this thickness appeared to be inconsistent with other gravity and topography data.

The image below shows the thickness of Enceladus’s ice shell, which reaches 35 kilometers in the cratered equatorial regions (shown in yellow) and less than 5 kilometers in the active south polar region (shown in blue).

In order to reconcile the different constraints, the researchers from the Laboratoire de Planétologie Géodynamique de Nantes (CNRS/Université de Nantes/Université d’Angers), Charles University in Prague, and the Royal Observatory of Belgium1 proposed a new model in which the top two hundred meters of the ice shell acts like an elastic shell.

According to this study, Enceladus is made up successively of a rocky core with a radius of 185 kilometers, and an internal ocean approximately 45 kilometers deep, isolated from the surface by an ice shell with a mean thickness of around 20 kilometers, except at the south pole where it is thought to be less than 5 kilometers thick. In this model, the ocean beneath the ice makes up 40% of the total volume of the moon, while its salt content is estimated to be similar to that of Earth’s oceans.

Since a thinner ice shell retains less heat, the tidal effects caused by Saturn on the large fractures in the ice at the south pole are no longer enough to explain the strong heat flow affecting this region. The model therefore reinforces the idea that there is strong heat production in Enceladus’s deep interior that may power the hydrothermal vents on the ocean floor.

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The Daily Galaxy via NASA, bbc.com and www2.cnrs.fr

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