New research has suggested that the core of Saturn’s moon Enceladus is similar to that of meteorites – specifically chondrites, non-metallic rocks formed from dust coalescing in the early Solar System. The research suggests not only that Enceladus formed earlier than thought, but also raises new questions about the possible habitability of the moon beneath its frozen surface.
Enceladus is thought to have a vast global ocean below its icy crust, and intermittently material is spewed out as plumes. In this study, published in the journal Nature Communications, Yasuhito Sekine of the University of Tokyo and his colleagues attempted to replicate the known composition of the liquids in the plumes.
Their results suggest evidence for serpentinization occurring in the ocean, a process through which primitive minerals are altered by hydration, indicating that the interior of Enceladus is similar to primitive meteorites from the early Solar System. Earth's core, too, is thought to be like a chondrite.
A previous study by Sekine and his colleagues found silica nanoparticles in the plumes erupting from the ocean of Enceladus, based on flybys by the Cassini spacecraft through the plumes. “The experiments performed in the present study show that in order to produce silica nanoparticles within Enceladus, hydrothermal reactions need to occur in a porous core made of rocks similar to chondrites,” Sekine told IFLScience.
This presents somewhat of a dilemma though. A chondritic core would suggest that Enceladus did not experience any melting of its rocks when it first formed, something dubbed a “hot start,” because if this were the case the rocks would not still be in this primitive state. This should also mean there isn’t the same level of hydrothermal activity, as evidenced by the plumes we see today, indicating that a recent heating event such as a large impact event may be the cause of the activity. This in turn creates complications for the possibilities of life on Enceladus.
“If the current hydrothermal activity was triggered by a relatively recent heating event, habitable environments within Enceladus would not continue as long as that of Earth,” said Sekine. “On the other hand, hydrothermal reactions within a chondritic core would be favorable for sustaining primitive life by providing a lot of hydrogen in terms of energy.”
This production of hydrogen would be caused by the presence of iron, which reacts with water to produce hydrogen, an energy source for primitive, life-like microbes called methanogens. The other main components of the core of Enceladus are silicon, oxygen, and magnesium.
Thus, while providing insight into the possible composition of Enceladus, this research also poses new questions about the habitability of Enceladus. The presence of hydrogen is key, but if it does turn out there was a relatively large recent impact, it could dampen any such hopes of habitability.
On October 28, the Cassini spacecraft is due to fly through the plumes of Enceladus again, and researchers will be hoping for new data on what is taking place in the interior of this intriguing icy moon.
Image in text: A cutaway view of the interior of Enceladus and its plumes. NASA/JPL-Caltech