Earth's moon might look like it's made of cheese,
but Jupiter's moon Io seems a lot more delicious.
I mean, look at this thing. It's like a giant pizza with all kinds of crazy toppings.
Io has all those blobs for a good reason. It's full of active volcanoes.
So many that it's the most volcanically active body in the solar system.
We're talking more than 150 active volcanoes -- some with 400 kilometer high eruptions.
But those weird looking spots are also a kind of mystery
because the volcanoes on Io aren't where astronomers expected to find them
which might mean that the moon has an underground magma ocean.
The mystery comes from how Io's volcanoes are thought to form
which has to do with the gravitational pull of Jupiter and two other moons: Europa and Ganymede.
As Io orbits Jupiter, the gravity from each of these worlds tugs its insides in a particular way.
It's called Tidal Flexing and it stretches the moon, deforming its surface by up to 100 meters at a time.
Io's insides are getting stretched and squeezed
and the friction from all that rock moving around produces a lot of heat.
Like, enough heat to melt the rock into magma in some spots.
So, for a long time, astronomers have been using what we know about the way Jupiter and its moons orbit
to predict exactly where the hot spots should be.
And you would think that Io's volcanoes would be right on top of those hot spots.
It would make sense for the magma to be erupting from the places that have the most of it,
but it turns out that's not where the volcanoes are.
In 2013, a group of researchers led by an astronomer named Christopher Hamilton, modelled Io's tidal flexing
to map out the warmer spots.
When they compared that map to the actual locations of the moon's volcanoes
they found that the volcanoes were shifted much farther east by 30 to 60 degrees.
They came with two main reasons why that could be.
The first possibility is that we're wrong about how fast Io rotates.
If it spins faster, then its insides might be heating up more and messing with the volcanic plumbing.
The hot spots could be in totally different places -- shifted east, for example.
Or, the model for Io might have been off
because of the magma ocean astronomers think is hiding below Io's surface.
Scientists have found evidence for an ocean like this before.
Back in 2011, a separate team of researchers predicted
that Io had a magma ocean 30 to 50 kilometres beneath the crust
which would help explain some unexpected measurements the Galileo probe detected
in Jupiter's magnetic field
In a paper published in the Astrophysical Journal Supplement Series in June, 2015
a third group, which included Hamilton, modelled how an underground magma ocean like that would affect
the flow of heat inside Io.
The ocean in their model would cover the entire moon and it would be kind of sponge-like, slowly moving
around below the surface, thanks to the tidal pull caused by Jupiter, Ganymede and Europa.
The researchers found that this flowing magma could explain the shift in the volcanoes' locations
by generating even more friction and heat as it moves.
Which means that the mystery of Io's misplaced volcanoes might just be
another piece of supporting evidence for the idea that there is a hidden layer of magma ocean
sloshing around inside the moon.
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