Astrophile is our weekly column on curious cosmic objects, from the solar system to the far reaches of the multiverse
Object: Europa鈥檚 subsurface ocean
Interesting property: Intense turbulence
As moons go, Europa is doing pretty well in the looks department. While other wrinkled and pockmarked planetary bodies look their age, Jupiter鈥檚 moon, despite being billions of years old, is one of the smoothest objects in our solar system.
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However, this moon is far from flawless. Europa is suspected to have a perpetually dark, liquid water ocean enclosed beneath a thick shell of water ice 鈥� around 40 per cent of which is covered with long, dark scratches and scars.
The prospect of liquid water places Europa near the top of the list of places in our solar system that might host alien life. However, it is hard to know what鈥檚 actually going on in the sub-surface ocean. Does it teem with alien microbes 鈥� perhaps even bigger creatures 鈥� or is it a vast, inky, sterile wasteland?
The only window we have on the ocean is its icy surface, so scientists try to read its criss-cross scars for clues. But whether this so-called chaos terrain can tell us about what鈥檚 going on underneath such a thick layer of ice is hotly disputed.
Oceanic chaos
The criss-cross pattern is likely to be caused by warmer and thinner regions of ice breaking and refreezing. It is much more abundant around the moon鈥檚 equatorial regions than at its poles 鈥� but why should this be the case?
Unlike on Earth, the temperature difference between the equator and poles cannot be explained by the effects of the sun because its light is too faint and Europa鈥檚 surface too reflective.
Another theory involves Jupiter鈥檚 gravitational pull, which would produce tectonic forces and heat up Europa鈥檚 ocean 鈥� but models have shown that this would heat the poles more than the equator.
The latest study suggests that turbulence in Europa鈥檚 ocean sculpts the chaos terrain on the icy surface. It was previously assumed that an effect caused by the moon鈥檚 rotation 鈥� known as the Coriolis force 鈥� dominates the ocean鈥檚 flow, funnelling heat to high latitudes. The new model instead relies on ocean currents caused by convection of the moon鈥檚 internal heat.
Mix for life
The team found that this produces a chaos terrain very similar to the one seen on Europa. 鈥淭he resulting flow is less organised, but more vigorous in the equatorial region,鈥� says researcher of the Max Planck Institute for Solar System Research in Lindau, Germany. 鈥淭his correlates nicely with the distribution of chaos terrain.鈥�
The model suggests that the ocean is extremely turbulent, with three strong ocean jets. So despite the thickness of Europa鈥檚 icy shell, it seems that properties of its ocean are writ in the ice. 鈥淲e may be able to understand Europa鈥檚 ocean just by looking at the surface,鈥� says Wicht鈥檚 colleague of the Georgia Institute of Technology in Atlanta.
A turbulent ocean would be beneficial for any life there because it would help shift nutrients from the sea floor into the rest of the ocean, says Schmidt鈥檚 other colleague, of the University of Texas at Austin. Microbes can live in stagnant water, but knowing the ocean is turbulent makes life much more likely.
Upcoming missions such as the European Space Agency鈥檚 , will map Europa鈥檚 chaos terrain via fly-bys in 2030, and potentially , will find out more 鈥� although it is just a concept at the moment.
Studies of Europa鈥檚 chaos terrain may have relevance beyond Jupiter鈥檚 moon. 鈥淚cy subsurface oceans may be commonplace in the outer solar system,鈥� says of the University of Oxford, a member of the ESA Science Working Team for JUICE. 鈥淛UICE will also search for any active plumes and vents, just like on Saturn鈥檚 moon Enceladus, to offer a glimpse into this icy ocean. This will be a great test of this sort of model for the icy worlds of our solar system.鈥�
Journal reference: Nature Geoscience Letters,
