Hello, friends, and welcome back to Sciency Words! That’s right, Sciency Words is back! I’m going to handle this series a little differently than I did before. I could explain what those differences are, but I think it’s better if we just dive right in so you can see for yourselves.
Since this is officially Europa Month here on Planet Pailly, we’re going to turn our attention to Europa, the sixth moon of Jupiter. When exploring alien worlds, scientists sometimes discover geological features that are not found here on Earth. When that happens, scientists need to invent new words to describe what they’re seeing. Here are a few of the terms used to describe geological surface features seen on Europa.
Chaos Terrain: For the most part, Europa’s surface is made of very smooth, very fresh-looking ice. But in some regions, we find these big, broken chunks of ice in a state of chaotic disarray. Imagine a bunch of icebergs breaking loose from a glacier. Now imagine that, before the icebergs drift too far, the water around them freezes, locking those icebergs in place. That’s basically what chaos terrain looks like. Oh, and chaos terrain tends to be discolored with some sort of reddish-brown substance. Click here to see some chaos terrain on Europa.
Linea (plural, lineae): From the Latin word for line, linea means… line. Reddish-brown lineae crisscross the surface of Europa. They appear to be cracks in Europa’s icy surface, cracks which have been filled in by a mixture of freshly frozen ice and more of that reddish-brown substance. Click here to see a color enhanced view of Europa’s lineae.
Lenticula (plural, lenticulae): From the Latin word for freckles, lenticulae are small, reddish-brown spots scattered all over the surface of Europa. They tend to be round, but they don’t appear to be impact craters, which means they’re probably caused by something happening beneath Europa’s surface. Click here to see a cluster of lenticulae on Europa’s surface.
Macula (plural, maculae): From the Latin word for spot, maculae are spots of discoloration on the surface of a planet or moon. Europa’s maculae are irregularly shaped blotches of reddish-brown color. At least one macula (known as Thera Macula) has been identified as a possible region of active chaos terrain formation. Click here for a closer look at Thera Macula.
It’s extremely cold in the outer Solar System, so cold that water behaves almost like a kind of rock. When thinking about icy worlds like Europa, it can be helpful to conceptualize water in that way. Water is a kind of rock. With that in mind, Europa’s icy surface is much like the rocky crust we have here on Earth, and Europa’s subsurface ocean of liquid water is sort of like the layer of molten rock that lies beneath Earth’s crust. And thus the surface features we see on Europa might be caused by processes similar to the tectonic and volcanic activity we experience here on Earth.
There are, of course, other geological terms associated with Europa, but for this post I wanted to focus on just these four. Europa’s chaos terrain, lineae, lenticulae, and maculae all have something important in common: that reddish-brown discoloration. Next time on Planet Pailly, we’ll try to figure out what, exactly, that reddish-brown stuff on Europa is.
Planet Pailly 
The Lenticula sounds really interesting, and I’d love for Europa Clipper to explain that phenomenon! And the chaotic parts, like chaos terrain, it sounds like Europa had to have been more liquid in the past. It sort of gives me a gut feeling that the moon froze rather suddenly, I mean the surface looks so crystalline!
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I think that’s a possibility. But the surface could also be continuously recycling itself, like Earth’s tectonic plates. That could also explain why it looks so smooth and fresh.
I do hope Europa Clipper and JUICE can give us more information on how the surface formed and how old it really is. That will tell us a lot about what’s going on beneath the surface, too.
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