Deep beneath its icy crust, the dark waters of Enceladus can swirl.
According to a new analysis of the layer of ice that covers the global oceans of Saturn’s moon, it seems that currents flowing there are very similar to those of Earth. If so, this means that the oceans of Enceladus may not be homogeneous after all.
Enceladus does not give up his secrets easily. Our first good look was in 1981, when Voyager 2 went on its way to the outer solar system. Images from the probe revealed a small ball of highly reflective ice, only 500 kilometers in diameter, crowded with craters and scarred by long cracks and ridges, suggesting geological activity.
Then, in 2010, a huge surprise: Saturn Cassini’s probe discovered liquid water geysers spraying fractures on the icy shell of Enceladus, evidence that the moon it was not ice all the way, but it housed a salty 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 stretch and stretch. the moon. This stress generates internal heating and geothermal activity and creates cracks in the surface ice.
Internal heating keeps the inner ocean liquid and spreads through cracks like geysers that fall to the surface and freeze. That internal heating would also generate vertical convection currents, similar to those seen on Earth, sending warmer water upward, where it would cool before circulating downward again.
Because Enceladus is so different from Earth, it is unclear whether its oceans may also be similar in other ways. Earth’s oceans are, on average, 3.7 kilometers deep. The 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 to the ice. We know that ice is dramatically thinner at the poles than at the equator and much thinner at the south pole, where the moonthe geysers explode. This, according to a team of researchers led by geophysicist Ana Lobo of Caltech, suggests that there is something more complex than simple vertical convection happening in the lower ocean.
Not surprisingly, thinner ice is associated with larger melting and thicker ice with greater freezing. This means that where the ice is thicker, the ocean is saltier, as only the water freezes and most of the salts are released back into the water. This makes the water below the ice denser, so it sinks to the bottom of the ocean.
In the merging regions, the opposite happens. The water is cooler and less dense, so it stays on top. Here on Earth, it translates into a kind of “conveyor belt” current. The water freezes at the poles and the denser, saltier water sinks to the bottom and flows in a stream toward the equator, while the warmer waters of the equator flow toward the poles where they are frozen, which causes colder and denser salt water to sink. etc.
The team developed an Enceladus computer model, based in part on our understanding of these conveyor belt currents, and the team found that a similar flow could reproduce the thicknesses observed in the moonthe ice.
Now, it is not clear if there is life in Enceladus. It is very far from the Sun, but due to internal geothermal warming, it may have chemosynthetic food webs similar to those found around hydrothermal vents in the deep, dark oceans of the Earth. If there is life hidden deep in the oceans of Enceladus, the team’s findings can help us figure out where to find it.
We know that the waters of Enceladus are salty; the water shown by Cassini of the geysers was revealed so much. If the team is right, the salt levels of these geysers can be really at the bottom, as they are expelled from the melting region and the waters around the equator can 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 are likely to be the most livable in life as we know it.
There is, at this time, no mission dedicated to Enceladus in the pipes. However, the Dragonfly mission to Saturn’s moon, Titan, the Europa Clipper dispatcher to study the frost and (possibly) Jupiter Europe’s icy moon, and the JUpiter ICy Moon Explorer (JUICE) could provide more light on world ocean circulation over these strangers. , icy monster.
The team’s research has been published in Geoscience of nature.