Welcome to a special A to Z Challenge edition of Sciency Words! Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms. In today’s post, Y is for:
Imagine a nice, smooth, clean sheet of asphalt: a parking lot, maybe, with no cracks or potholes or blemishes of any kind. Just looking at it, you would know, with a reasonable degree of certainty, that this asphalt had been laid down recently. It’s new. It is, in effect, a young surface.
In much the same way, planetary scientists can look at the surface of a planet or moon and infer, with a reasonable degree of certainty, how young or old that surface must be. Look at the Moon or Mercury; they’re covered in craters, showing that their surfaces must be very, very old. Or look at Mars, where some regions are more heavily cratered than others, implying (intriguingly) that some surfaces are relatively old and some are relatively young.
And then there’s Europa, one of Jupiter’s moons. Europa may be covered in weird, orangey-red cracks, and it may have a few other orangey-red blemishes, but overall it’s surprisingly smooth, and there are very few craters. This makes Europa look a whole lot younger than it actually is. In fact, Europa is said to have the youngest-looking surface in the whole Solar System.
Europa’s surface is made of ice, specifically water ice. This is not so uncommon for a moon in the outer Solar System. It’s so cold out there that water behaves like a kind of rock.
But unlike most other icy moons, Europa must be doing something to get rid of old, crater-y surface ice and replace it with new, clean, smooth ice. And once you really start thinking of water as a kind of rock, you might be able to guess what Europa’s doing. As stated in this paper from Nature Geoscience: “[…] Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics.”
Except unlike Earth’s techtonic plates, which float atop a layer of magma (liquid rock), Europa’s plates would be floating atop “magma” that is actually liquid water—twice as much liquid water as we have here on Earth, according to some calculations.
And while liquid water may or may not be necessary for life, we do have good reason to suspect that any place that has liquid water might also have life. Personally, based on everything else I’ve learned about Europa, I’d be more surprised if we didn’t find something living there.
Next time on Sciency Words A to Z, I have a prediction for the future.