Like Earth, Enceladus could have ocean currents

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According to a new study, the global ocean of the moon Enceladus is not homogeneous. Currents very similar to those of the Earth could circulate there under twenty kilometers of ice.

Enceladus, Saturn’s sixth largest moon, is a small ball of ice 500 kilometers in diameter. Despite its size, the object has attracted the attention of researchers since 2014. We know, in fact, thanks to the American Cassini probe that jets of steam emanate from its depths, suggesting the presence of a global ocean below the surface.

Differences and similarities

The ocean of Enceladus remains quite different from those of Earth. Our oceans are relatively shallow (an average of 3.6 km deep), cover about three-quarters of the surface, are warmer at the top thanks to the sun’s rays and cooler at the depths.

Enceladus, for its part, displays an a priori global ocean about thirty kilometers deep nestled under several kilometers of ice. This mass of water is therefore cooled at the top, near the ice shell, and warmed at the bottom by the core heat of the moon.

Despite these differences, the moon’s ocean and those of Earth also show some similarities. We know for example that they are savory. A few months ago, a study also revealed to us similarities in pH. Finally, according to a new analysis, the oceans of Enceladus could also have currents similar to those of Earth.

This new work, led by Caltech graduate student Ana Lobo, builds on Cassini’s measurements as well as Andrew Thompson’s research. A professor of environmental science and engineering, the latter has studied how ice and water interact to cause the oceans to mix around Antarctica.

Illustration of the Cassini probe flying through plumes of Enceladus in October 2015. Credits: NASA / JPL-Caltech

Both different and similar

As said above, the oceans of Enceladus and Earth share an important characteristic: they are salty. And as these results published in Geoscience of nature, changes in salinity could act as engines for Enceladus’ ocean circulation, just as they do in the Earth’s Southern Ocean around Antarctica.

Cassini’s gravitational measurements and heat calculations have indeed already revealed that the frozen shell of the moon is thinner at the poles than at the equator. As Andrew Thompson points out, there would therefore be more melting at the level of the polar regions and more freezing at the level of the equator.

However, salt water that freezes tends to release salts into the environment, which makes the surrounding water heavier, causing it to flow. The opposite effect occurs at the poles.

Knowing the distribution of the ice allows us to impose constraints on traffic patterns.“, Summarizes Ana Lobo. “Our computer model suggests that the regions of freezing and melting, identified by the structure of the ice, would be connected by ocean currents. This would create a circulation from the pole to the equator which influences the distribution of heat and nutrients“.

Enceladus (foreground) drifts past Saturn’s rings as Titan looms behind. Image: NASA / JPL-Caltech / Space Science Institute

A prime target for life

Remember that a few months ago, a study announced the presence of ammonia (a potential source of fuel for life) in this ocean. Of works Recent people have also pointed out that the Enceladus Ocean may be old enough to allow organisms to thrive, but not “too old” to be able to sustain it.

We also know that this moon offers hydrothermal activity located near the core-mantle boundary. However, microorganisms evolve in similar environments at the bottom of the Earth’s oceans.

Add to that ocean currents that can distribute heat and nutrients, and you’ve got a prime target for astrobiologists looking for signs of life.

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