What I Learned Today

This just in: Europa, the moon of many mysteries, has been declared to have the icy equivalent of plate tectonics.

It’s been known for decades that Europa’s icy surface moves around, because we see bands that cut across pre-existing features. These are dubbed “spreading” or “dilational” bands because if you roll back time by removing them, the earlier features line up in their (presumed) prior orientation like puzzle pieces. For example:

(from Prockter et al., 2002, JGR, 107(E5), 10.1029/2000JE001458)

But if there are areas where the ice is spreading apart, then one of two things must be true:

1. There are other areas that consume ice so the total surface area is constant.
2. Europa is expanding.

On the Earth, new crust is created at the mid-ocean ridges. It moves outward and then is consumed at subduction zones (like the coast of California). But to date, no one has seen anything like that on Europa.

At this year’s Lunar and Planetary Science conference, Simon Kattenhorn and Louise Prockter presented the first evidence for a subduction zone on Europa. It’s curiously curved, and they’ve only found one so far, but it could provide the missing part of the story of how Europa’s surface changes over time. There are some remaining details to work out (ice can’t subduct exactly the way crust does on Earth), but it’s certainly intriguing!

You can read Kattenhorn and Prockter’s two-page abstract here: Subduction on Europa: The case for plate tectonics in the ice shell. For a very nice, accessible discussion of the context and importance of this work, I recommend Emily Lakdawalla’s discussion (and images).