There are plumes aplenty on Io, Jupiter’s volcanic satellite and one of its Galilean moons. Where Ganymede has an introverted warm core sandwiched with ice, Io is its extroverted sibling, expelling eruptions of colors from its yellowish, animated surface. But perhaps the most fascinating aspect of Io, aside from its resemblance to pizza, is its crust’s capacity to rise.
Io is locked in Jupiter’s orbit, but as the innermost moon, gravitational forces from nearby Ganymede and Europa jostle her on an irregular path. The tidal stresses are so powerful that Io can bloat or shrink up to about 330 feet (or 100 meters). The phenomenon is similar to the heat that’s emitted from a wire that’s bent back and forth rapidly, as scientists the Hawaiian Volcano Observatory explain. Earth bulges, too, which also coincides with our ocean tides, but it’s infinitesimal compared to Io’s swelling and can only be measured using very sensitive tools.
As Io’s rocky crust expands, the friction generates a lot of heat, and that’s what fuels the moon’s molten innards. It’s big part of Io’s charisma; she’s expressive and regularly changes her appearance — at least on the face we can see, since she always keeps one side facing away from Jupiter. The frequency of lava spillovers wipes the surface clean of craters, and those that do form don’t last too long.
The lava isn’t your standard burble, either: It can rocket up to 250 miles (about 400 km) high. The most renowned plume comes from a volcano named Prometheus, an eruption that wandered nearly 50 miles (75 to 95 km) between images taken by Voyager flybys in the 1970s and Galileo two decades later.
It’s not the first time Io’s volcanoes seem to have picked up and moved. Using computer models, researchers noticed volcanoes shifted to where they shouldn’t be, and they would have written it off as an anomaly if it wasn’t a distinctive pattern. A study published last year suggests a hybrid model of gravitational smooshing and friction from an underground magma ocean. Best of all, that points to possible life, a potential that pops up in oceans all over the solar system.