Deep beneath its icy crust, the dark waters of Enceladus can swirl.
According to a new analysis of the ice cover covering the global oceans of Saturn’s moon, it appears that there are currents very similar to Earth’s. If so, it means that Enceladus’ oceans may not be homogeneous after all.
Enceladus does not easily reveal its secrets. Our first good look at it came in 1981, when Voyager 2 was en route to the outer solar system. The probe images revealed a small ball of highly reflective ice, only 500 kilometers (310 miles) across, pockmarked with craters and marked by long cracks and mountain ranges, indicating geological activity.
Then, in 2010, a huge surprise: Saturn probe Cassini discovered liquid water geysers spraying from fractures in Enceladus’s icy shell – proof that the moon was not all the way down ice, but with a liquid salty ocean.
The combination of liquid water and cracks in the ice helped scientists understand how Enceladus works. As Enceladus makes its elliptical, 1.37-day orbit around Saturn, the shifting gravitational forces pull and extend the moonThis stress generates internal heating and geothermal activity, creating cracks in the surface ice.
The internal heating keeps the internal ocean liquid, and it sprays through the cracks like geysers, falling to the surface and freezing again. That internal heating would also generate vertical convection currents – similar to those on Earth – that send warmer water up, where it would cool before circulating back down.
Because Enceladus is so different from Earth, it’s unclear whether its oceans can be similar in other ways as well. Earth’s oceans are on average 3.7 kilometers deep. Enceladus’s is at least 30 kilometers deep and covered with 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 the ice at the poles is considerably thinner than at the equator, and much more at the South Pole, where the moonGeysers erupt. According to a team of researchers led by Caltech geophysicist Ana Lobo, this suggests there’s something more complicated than just vertical convection in the ocean below.
Thinner ice is – probably unsurprisingly – probably associated with more melting and thicker ice with more 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 causes the water under the ice to become denser so that it sinks to the bottom of the ocean.
The opposite happens in melting areas. The water is fresher and less dense, so it stays at the top. Here on Earth, this results in a sort of “assembly line” flow. Water freezes at the poles, and the denser, saltier water sinks to the bottom and flows in a current towards the equator, while warmer water flows from the equator to the poles where it is frozen, resulting in a denser, cold salt water that sinks, and so on.
The team developed a computer model of Enceladus, based in part on our understanding of these conveyor belt flows, and the team found that a similar flow contained the observed thicknesses in the moonis ice.
Now it is unclear whether there is life on Enceladus. It is very far from the sun, but due to its internal geothermal heating, it may have chemosynthetic food webs similar to those found around hydrothermal vents in Earth’s deep, dark oceans. If life is hidden deep in the oceans of Enceladus, the team’s findings could help us figure out where to find it.
We know that the waters of Enceladus are salty; the water that Cassini sampled from the geysers revealed just as much. If the team is right, the salinity levels in those geysers may well be at the bottom, as they are thrown out of the melting area and the water around the equator can be much saltier.
We also know that Earth’s ocean currents play a role in nutrient distribution. A deeper knowledge of the salinity and distribution of nutrients would help to highlight the regions of Enceladus that are probably the most habitable for life as we know it today.
At the time of writing, there are no special missions to Enceladus in the pipelines. The Dragonfly mission to Saturn’s moon Titan, the Europa Clipper sent to study Jupiter’s icy and (possibly) geyser-spouting moon Europa, and the JUpiter ICy moons Explorer (JUICE) could all shed more light on the global ocean circulation on this strange moon. , yellow worlds.
The team’s research is published in Nature Geoscience