EUROPA has more water than Earth.
But the frozen moon of Jupiter is just one quarter its size.
Now astrophysicists have discovered Europa has something else we do: tectonic activity.
And that could be a major boost in the likelihood of life evolving in the oceans between its firey core and icy crust.
It’s tectonic activity. But not as we know it.
Europa spins about Jupiter on a slightly elliptical orbit. This means it swings close to the gas giant before looping somewhat further away.
The slight differences in gravity this produces flexes the moon’s core — creating the friction necessary to create a molten heart.
This warms the ice from below — likely creating a vast subsurface ocean of liquid water.
But is there any chance this ocean can harbour life, being some 100 kilometres under rock-hard ice and so far of our own warmth-giving Sun?
New simulations reported by the American Geophysical Union have just solved one of the many challenges such life would face.
A nutrient flow.
Essential minerals and compounds must circulate in a planet’s — or moon’s — ecosystem to maintain any cycle of life.
On Earth, that is done through tectonic activity.
Here, tectonic plates of rock are constantly pushing against each other.
The result is often subduction — where the old Earth’s crust gradually slips into the molten mantle below. Elsewhere, new rock cools as it rises — taking the place of that which has been swallowed up.
It’s a process that refreshes the supply of vital nutrients on our planet’s surface. Otherwise, it would all be eroded — and consumed — away.
Turns out a similar process is likely to be happening on Europa.
Except the refreshing nutrients aren’t coming from below.
They’re coming from above.
Plate tectonic activity may be happening in Europa’s icy shell. Simulations show plates of rock-hard-ice could be grinding into each other, forcing the surface layer down to later melt in the liquid ocean below.
“We have this evidence of extension and spreading, so the question becomes where does that material go?” said Brandon Johnson, an assistant professor at Brown University’s Department of Earth, Environmental and Planetary Sciences.
“On Earth, the answer is subduction zones. What we show is that under reasonable assumptions for conditions on Europa, subduction could be happening there as well, which is really exciting.”
INGREDIENTS FOR LIFE
As the ice is forced downward, it would carry dust and compounds that have been falling on Europa’s surface into the potentially life-giving liquid water.
This rich ‘seasoning’ of oxidants and other chemicals are the building blocks — and foods — of life.
“If indeed there’s life in that ocean, subduction offers a way to supply the nutrients it would need,” Professor Johnson says.
It all depends on the behaviour of Europa’s ice.
There is evidence Europa’s shell is made up of two layers of ice.
One is a thin outer casing that is intensely cold (and dirty, as the moon’s orange markings betray). This sits on a layer of slightly warmer, convecting ice.
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The warmer ice is less dense than the crust, allowing the crust to sink until it cools to the temperature of the ice below.
But the new simulation shows that the presence of salts in Europa’s ice shell add enough difference in densities for it to subduct in the same manner as tectonic plates.
“Adding salt to an ice slab would be like adding little weights to it because salt is denser than ice,” Professor Johnson says. “So rather than temperature, we show that differences in the salt content of the ice could enable subduction to happen on Europa.”
This could all contribute to a cycle similar to that produced by the magma under Earth’s mantle. One such sign is cryovolcanism, where the salty contents of Europa’s ocean are sprayed out on its icy surface.