A probe sweeps through space. Roughly 4.2 million kilometers (2.6 million miles) away, you sit and watch images of another world appear. You notice a mottled surface, and on its horizon, jetting an incredible 260km (162mi) above its surface, a plume.
This is the first volcano ever seen erupting outside your planet.
This is a world where volcanic plumes are sulfur dioxide snow, and are so large they can be seen from Earth orbit by the Hubble Space Telescope, and from Earth-based telescopes as outbursts of infrared. Tectonics are driven by tides rather than internal heat; volcanoes vent ultramafic lavas hotter than anything seen on Earth in billions of years. 425 volcanic centers, 70 of them currently active, rework the surface at a remarkable rate of 1 centimeter (over a third of an inch) per year. This world is 25 times as volcanically active as Earth, bumping us to second place for geologic activity, but is barely larger than our own Moon. It’s the only other planet in the solar system we know of that has active volcanoes. It claims the prize for longest lava flows. And if folks before the 20th century had known that, they might have named it Vulcan. Galileo called it Medician Planet I, then Jupiter I when he realized it was a moon. Scientists in the 19th century named it Io.
Isn’t she a beauty?
She was a bit of a surprise, but even before Voyager snapped that famous image of the first volcano caught erupting outside Earth, scientists suspected they’d find active volcanoes there. Io, you see, is caught between Jupiter’s enormous bulk and two other substantial moons, Europa and Ganymede. We’ve got tides up to 18 meters (60 feet) high, caused by the tug of our one moon: Io’s tides are more than 100 meters (328 feet) high – and mind you, that’s 100 meters of rock. It takes a tremendous amount of force to move that much solid stuff, and the solid stuff heats up to remarkable temperatures. It’s how a world far tinier than ours can sustain eruptions Earth hasn’t been hot enough to experience in billions of years.
This is a world that’s undeniably alien, and yet eerily familiar. Visit Hawaii’s volcanoes, and you can get a sense of what’s going on with Io. Yes, her explosive eruptions are driven more by sulfur dioxide than water and carbon dioxide like ours are, and her lavas average a scorching 1,600°C (2,900°F) compared to our chillier lavas (1200-1300°C/2200-2400°F). Yes, outside of the searing-hot areas of active volcanism, the surface is a frigid -150°C (-300°F). And, of course, things go higher in that thin atmosphere and low gravity – Old Faithful, for instance, would jet a whopping 37 kilometers (23 miles) high there. But outside of all that, the volcanoes aren’t so different. They erupt lavas composed of chemicals we’re familiar with here: sulfur dioxide, silicon, oxygen, iron, magnesium, potassium, sodium, calcium. They erupt in patterns that are quite familiar.
For instance, we can watch a curtain of fire emerge from a fissure at Tvashtar Catena:
We can see lava tubes, complete with skylights:
We can see calderas, some complete with lava lakes:
We’ve mapped lava fields, volcanic domes, pyroclastic deposits, mountains and plains – oh, and did I mention, we’ve done a geologic map of the place? That’s right. A whole geologic map of a whole other world, created by the USGS.
That map showed us another fascinating fact about Io: there aren’t any impact craters on it. Every other body in the solar system has got one, but Io doesn’t. Its volcanoes busily erase every single one. Amazing, am I right?
There’s more to be said about this beautiful, brilliant moon. Far more. And I will say it someday, after I’ve had a chance to read up a bit further (and after we’ve finished with Mount St. Helens, which we have not – not by a long shot). Consider this a mere introduction, and a promise, and a reminder that geology happens in far more places than we typically consider. The Earth sciences can be quite unearthly.
Not to mention, heartbreakingly beautiful.
References:
ASU News: “Geologic map of Jupiter’s moon Io details an otherworldly volcanic surface.” Last accessed 9/7/2012.
How Volcanoes Work: “Volcanism on Io.” Last accessed 9/7/2012.
NASA Science: “Io’s Alien Volcanoes.” Last accessed 9/7/2012.
NASA Solar System Exploration: “Volcanism on Io.” Last accessed 9/7/2012.
USGS Hawaiian Volcano Observatory: “An Eye on Io’s Volcanism.” Last accessed 9/7/2012.
USGS: “Geologic Map of Io.” Last accessed 9/7/2012.
This is really cool, Dana! OTOH, I’m wondering if, strictly speaking, we can refer to it as ‘geology.’
The term ‘iology’ works for me.
Although, if we think of ‘geology’ as the study of processes involving rocks, tectonic plates, and the surface of a planet, then that works, too. I don’t think the term was meant to be as specific as people make it out to be.
This is awesome, Dana.
thanks. Great fun to catch up on our own secondary solar system around the brown dwarf (Jupiter)
Great stuff. I always learn something here.
On one of the geeky science shows I’ve seen, Linda Morabito describes how she was in the lab (JPL?) alone, late at night watching that image of Io slowly being scanned a line at a time. At first, she thought the plume was another Jovian moon or perhaps a star. After eliminating those possibilities, it dawns on her what she is seeing and she describes the joy and wonder of being the only human on the planet who knows that volcanoes erupt on other worlds.
Thanx so much, Dana Hunter.
cope, it was a BBC Horizon documentary about the Voyager spacecraft missions. Linda Morabito was working as an optical-navigation technician, identifying moons and stars on deliberately overexposed pictures so that their directions can be inputs for improving estimates of the spacecrafts’ positions. But when she saw that odd shape, she tried to find out what it was. Was it some known moon? No known one was in that direction. Was it some unknown one? It would have been too big to escape discovery from the Earth. Was it some camera artifact? No known one looked like that. So it must be something on Io itself. She found the latitude and longitude of that shape, and it matched the latitude and longitude of a feature that looked volcanic. But despite the remarkable youth of Io’s surface, nobody was willing to claim that any of Io’s volcanoes were active.
There were hints of Io volcanism observed before that discovery, but there were alternate hypotheses for most of them, like sputtering from evaporite deposits. That Io had active volcanoes had likely seemed too far-fetched to most planetary scientists. As one of their number had memorably noted, extraordinary claims require extraordinary evidence.
What heats up Io? It’s in an orbital resonance with two of the three other big moons of Jupiter: for every 4 orbits Io makes, Europa makes close to 2 and Ganymede close to 1. Europa gives Io a forced orbital eccentricity, making it alternately go closer to and farther from Jupiter. This makes Jupiter’s tides alternately stronger and weaker, thus kneading Io and heating it.