Enceladus could have a porous core that would allow to have an ocean of liquid water for billions of years

Scheme of Enceladus interior (Image Surface: NASA/JPL-Caltech/Space Science Institute; interior: LPG-CNRS/U. Nantes/U. Angers. Graphic composition: ESA)
Scheme of Enceladus interior (Image Surface: NASA/JPL-Caltech/Space Science Institute; interior: LPG-CNRS/U. Nantes/U. Angers. Graphic composition: ESA)

An article published in the journal “Nature Astronomy” describes a research that presents a possible explanation for the long-term existence of hydrothermal activities and an underground ocean of liquid water on Enceladus, one of Saturn’s moons. A team of researchers led by Gaël Choblet of the University of Nantes in France analyzed data collected by the Cassini space probe concluding that a porous core can be a key factor in generating heat for billions of years supporting an environment potentially favorable to life.

The mission of the Cassini space probe ended on September 15, 2017 leaving a huge legacy of information. Among the great discoveries made thanks to Cassini there’s the existence of an ocean beneath Enceladus’ frozen surface. The data collected are extremely interesting but also show some problems with the possibility to sustain the environment for a long time without it freezing.

At the origin of everything there’s the gravity of the planet Saturn that literally deforms Enceladus as it approaches and moves away to it in its elliptical orbit. The friction generated in the moon’s core by that deformation warms the underground ice however according to calculations the heat lost due to the geysers that eject water and other materials at Enceladus’ south pole should lead to freezing that ocean within about 30 millions of years. In short, the activity would’ve ended over 4 billion years ago.

According to the authors of this new research, the explanation could be in the porous nature of Enceladus’ core. That type of structure would allow the water to infiltrate inside it and gradually warm up thanks to the heat generated by the friction generated by Saturn’s gravity.

The water inside the core becomes very hot and the detection of very small rock grains ejected with the geysers indicates chemical reactions occurring at temperatures of at least 90° Celsius (194° Fahrenheit). The water hotter than the surrounding environment starts rising until its heat starts being transmitted to the seafloor.

The Enceladus ocean could be dotted with hotspots where hot water rises from the depths and also brings minerals. In the south pole that “dirty” water is ejected in the geysers but in the other ocean areas the minerals could enrich the environment. According to the researchers, the process is very slow but over the course of millions of years all the water in the Enceladus’ ocean could pass through its core.

The presence of hydrothermal sources is considered one of the possible nurseries in which the first life forms on Earth were born and something like that could have happened on Enceladus. That’s why this environment is considered so interesting and has been at the center of a growing number of studies.

During the Cassini mission the characteristics of Enceladus and its ocean were detected with more and more details. According to the authors of this research, their conclusions explain the presence of an underground ocean, the fact that the ice crust is thinner at the south pole and hydrothermal activities.

Not all has been explained: for example, it’s not yet clear why Enceladus’ north pole is dotted with ancient craters while the south pole is characterized by a relatively new crust. The study of the data collected by the Cassini space probe continues and many scientists hope for a new mission with more advanced instruments that could provide more accurate details but those are long-term projects that are being discussed.

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