For the last few weeks, we’ve been touring the moons of Jupiter and learning about some of the scientific terms used to describe the weird geological features we’ve found there. Today, we conclude this Jovian moons series with the term:
Meet Io, Jupiter’s fifth moon and the inner-most of the Galilean moons. Io, say hello to the nice blog readers.
Oh jeez. I’m sorry you had to see that. Io is sort of caught in a gravitational tug of war between Jupiter and the other Galilean moons. You’d feel queasy too if you were constantly being yanked back and forth by all that gravity.
The result is that Io is the most volcanically active object in the Solar System. Just about any time you look at Io, its sulfur volcanoes are erupting.
A Caldera by Any Other Name…
Astronomers use the word patera (plural, paterae) when discussing Io’s volcanoes. The term comes from the Latin word for flat dish, and the name is appropriate.
Paterae don’t look much like the kind of volcanoes we typically imagine. They aren’t raised, mountain-like features but rather flattened, crater-like depressions. If you know what a caldera is, a patera is basically the same thing.
How Calderas… I Mean, Paterae… Form
Picture this: somewhere on Io, we find an underground chamber full of a nasty, sulfur-rich brew. The temperature in this chamber rises, and the pressure builds up. Suddenly, an eruption occurs, and Io spews that sulfur mixture all over its surface.
As that subterranean chamber empties, the ground above it starts to sink. The resulting pit-like surface feature is a patera. Or a caldera. They really are the exact same thing. (Here’s a short video demonstrating the caldera/patera formation process).
Paterae are not unique to Io. They’ve also been observed on Mars, Venus, and Titan, among other places. They’re also found on Earth, except you’re not supposed to call it a patera if it’s on Earth.
Patera vs. Caldera: What’s the Difference?
If you really want to, you can use the word caldera when referring to Io’s volcanoes, or similar volcanoes on other worlds. That usage seems to be acceptable. But it is unlikely that you will ever see the word patera used for such features here on Earth.
I think there’s a bit of geocentrism at work here. A lot of planetary features have one name on Earth and some other name everywhere else. You’ll sometimes find Earthly terminology used off-world, because Earth terms are more familiar to the average reader; the reverse is rarely if ever true.
Which is fine. I’m not judging. A little linguistic geocentrism makes sense to me, at least at present. In some distant Sci-Fi future where humanity has spread across the Solar System and beyond… at that point, things like the caldera/patera distinction might seem a bit silly.