The global ocean of Enceladus does not sit still under its ice shell. Instead, it could potentially host massive ocean currents caused by changes in salinity.
Ocean world
The tiny world of Enceladus, Saturn’s sixth largest moon, should by no means be that interesting. It’s no more than 1/7 the width of our own moon and has a surface completely covered with water ice – nothing out of the ordinary. But in 2014 the NASA Cassini mission discovered something surprising: plumes of water sprayed through cracks in the ice.
Further studies revealed that the icy crust of Enceladus hides a fascinating secret: a global ocean of liquid water. In fact, the little moon could have more liquid water than the earth.
But this ocean is almost completely different from the one we see on earth. The oceans on our planet are relatively shallow – only a handful of kilometers deep. They don’t even completely cover the planet. And they are heated from above (via sunlight), with temperatures falling the lower the deeper you go.
The ocean of Enceladus is warmed from below by the molten interior of the moon and is likely more than 30 kilometers deep.
Salty currents
But the two oceans may have something in common: massive currents that move large amounts of water over great distances. On earth, these currents are mainly driven by temperature fluctuations. Equatorial water tends to be warmer than the poles due to the increased sunlight, and currents come in to try to equalize these temperatures.
The currents on Enceladus would work differently, however, according to a new study by CalTech PhD student Ana Lobo. Observations with Cassini showed that the ice shell is thinner at the poles and thicker at the equator. It is likely that the ice at the poles will melt while the ice at the equator freezes.
The ocean under all the ice could be churned due to varying degrees of saltiness. Photo credit: NASA / JPL / Space Science Institute
When the ice melts and freezes, it can change the local salt concentration. For example, when salt water freezes, the salt is left behind and the remaining water becomes heavier. The heavy water sinks in this region and rises where the ice melts.
“If we know how the ice is distributed, we can restrict the circulation patterns,” explains Lobo.
With a computer model in hand, Lobo and her colleagues discovered that Enceladus may host a large pole-to-equator system of ocean currents that could hold potential nutrients for life.
According to co-author Andrew Thompson, “Understanding which regions of the subterranean ocean might be most hospitable to life as we know it could one day influence efforts to find signs of life.”
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