Deep beneath its icy crust, the dark waters of the Enceladus may swirl.
According to a new analysis of the ice sheet that covers the global oceans of Saturn’s moon, currents very similar to those of the Earth seem to flow there. If so, this means that Enceladus’ oceans may not be homogeneous after all.
Enceladus does not give up his secrets easily. Our first good look came in 1981, when Voyager 2 made its way to the outer solar system. The images of the probe revealed a small highly reflective ice ball, with a radius of only 500 kilometers, with craters and scars with long cracks and mountain ranges, suggestive of geological activity.
Then, in 2010, a huge surprise: the Saturn Cassini spacecraft discovered the geysers with liquid water spray from the fractures in the frozen shell of the Enceladus – proof that month it was not ice to the end, but a salt liquid ocean.
The combination of liquid water and cracks in the ice helped scientists understand how Enceladus works. As Enceladus makes its 1.37-day elliptical orbit around Saturn, the changing gravitational forces pull and stretch to month. This stress generates internal heating and geothermal activity and creates cracks in the ice on the surface.
Internal heating maintains the liquid of the inner ocean and spreads through cracks in the form of geysers, which fall to the surface and freeze. This internal heating would also generate vertical convection currents – similar to those observed on Earth – sending warmer water upwards, where it would cool before circulating backwards.
Because Enceladus is so different from Earth, it is unclear whether its oceans may be similar in other ways. The Earth’s oceans are, on average, 3.7 kilometers (2.3 miles) deep. Enceladus is at least 30 kilometers deep and is covered by 20 kilometers of ice.
We can’t really see what’s going on in that ocean, but there are clues in the ice. We know that ice is dramatically thinner at the poles than at the equator and much more at the south pole, where monththe geysers erupt. This, according to a team of researchers led by geophysicist Ana Lobo of Caltech, suggests that there is something more complex than just vertical convection happening in the ocean below.
Thinner ice is – probably surprisingly – probably associated with higher melting and thicker ice with higher freezing. This means that if the ice is thicker, the ocean is saltier because only the water freezes and most of the salts are released back into the water. This makes the water under the ice thicker, so it sinks to the bottom of the ocean.
In melting regions, the opposite happens. The water is fresher and less dense, so it stays on top. Here on Earth, a kind of “conveyor belt” current results. The water freezes at the poles, and the denser and saltier water sinks to the bottom and flows in a current towards the equator, while the warmer waters from the equator flow to the poles where they are frozen, resulting in the sinking of cold and denser salt water. Further.
The team developed a computerized model of Enceladus, partly based on our understanding of these conveyor belt currents, and the team found that a similar flow could reproduce the thicknesses observed in monthice.
Now, it is not clear if there is life on Enceladus. It is very far from the Sun, but due to internal geothermal heating, it may have chemosynthetic food webs similar to those found around hydrothermal vents in the deep and dark oceans of the Earth. If there is a life hidden deep in the oceans of Enceladus, the team’s discoveries can help us figure out where to find it.
We know that the waters of the Enceladus are salty; the water sampled by Cassini from the geysers revealed just as much. If the team is correct, the salt levels in those geysers may actually be on the bottom, as they are discharged from the molten region, and the waters around the equator may be much saltier.
We also know that ocean currents on Earth play a role in the distribution of nutrients. A deeper knowledge of salinity levels and nutrient distribution would help highlight the regions of Enceladus that could be most livable for life as we know it.
At the time of writing, there are no dedicated missions to Enceladus in the pipelines. However, the Dragonfly mission to Saturn’s moon, Titan, Europa Clipper has been sent to study Jupiter’s frozen moon and (possibly) Europa geyser, and JUpiter ICy’s Moon Explorer (JUICE) could shed more light on ocean circulation. world over these strange, icy worlds.
The team ‘s research was published in Geoscience of nature.