2021 has so far been an explosive year on our planet, but it’s not the only place in the Solar System where volcanoes have been making the news.
This week moon rocks returned to Earth on China’s Chang’e-5 mission revealed that the Moon was volcanically active a billion years more recently than previously thought. Last month scientists found evidence that Arabia Terra in northern Mars experienced thousands of “super eruptions” during a 500 million year period that could have changed the red planet’s climate.
Neither the Moon nor Mars are geologically active anymore, but there are plenty of places where “space volcanoes” can be found … though they’re not quite what you may expect.
“Our view of volcanoes is very much biased towards how they look on Earth—a conical shaped mountain, often with a snowy peak that erupts some kind of molten hot rock,” said Natalie Starkey, a geologist and cosmochemist and author of “Fire and Ice: The Volcanoes of the Solar System,” which published last week. “It was only from NASA’s Voyager missions that we found out that there were volcanic worlds elsewhere, but those volcanoes don’t look like those on Earth.” Starkey’s excellent book is the first to examine these extra-terrestrial volcanoes of our Solar System.
It’s an explosive read in more ways than one.
“There are some that are similar to Earth’s volcanoes in the inner Solar System—such as volcanoes on Venus and the 15 miles/25 kilometres high Olympus Mons on Mars, which looks very much like Mauna Kea in Hawaii,” said Starkey. “When we get to the icy moons we find volcanic behaviour, but not necessarily conical-shaped mountains.”
Volcanoes are a part of the efforts a planetary body makes to cool itself down, releasing excess heat into space. For geologists it’s instant evidence that a world is active. “The same thing happens even on icy worlds—they’re still warmer on the inside than on the outside and that heat wants to move,” said Starkey. “So it only takes a slight temperature change to turn frozen water, methane or ammonia into a liquid.” So on an icy world it’s liquid water/ammonia/methane rather than liquid rock that spews out of a warm core.
Yes, space volcanoes are pretty weird—and they get even weirder.
Here’s where you’ll find them in the Solar System—and they’re not where you think they are:
Venus: second planet from the Sun
Venus is the new Mars, with five missions due to visit in the next decade. But should it be on this list? “We don’t have any proper proof that it’s still erupting today,” said Starkey. “But there’s a lot of evidence to suggest that it does have active volcanoes on its surface.”
The weird thing about Venus is that its surface is all the same age—about 500 million years old—largely because it doesn’t have plate tectonics, as we have on Earth. “It’s got a similar amount of heat to lose as Earth because it’s about the same size, so it builds up and then there’s a huge event where all that heat is released over a few hundred million years,” said Starkey.
There are probably about 37 volcanoes that could still be active and may have erupted lava and gases recently, but the atmosphere is hard to see through—hence the bevy of imminent exploration missions, like DAVINCI+, which will include a lander.
Io: moon of Jupiter
The most volcanically active world in the Solar System, Io is the innermost Galilean moon of Jupiter and thought to be home to an underground ocean of magma. “It’s got a constant heat source because of the tidal heating from Jupiter,” said Starkey. Io is in a constant gravitational tug-of-war with Jupiter and the other big moons, so much so that it changes shape during its 42-hour orbit.
It’s that constant friction and energy that makes Io so hot—and therefore so volcanic—so much so that an ocean of magma exists beneath its surface. Io features eruptions many orders of magnitude bigger than what happens on Earth today. “It should continue being so volcanic for as long as it is next to Jupiter and the other Galilean moons.”
Europa: moon of Jupiter
Europa—the fourth largest of Jupiter’s 79 moons—has fractures in its icy surface that make it look like a “veiny eyeball.” That’s a clue to its volcanism. “Europa is almost certainly volcanically active,” said Starkey. “The easiest way to tell is its surface—if it’s covered by craters that indicates that it’s not been resurfaced.” There are a few crater visible on Europe, but not many. “It’s geologically interesting do it must have been active recently,” she said.
Enceladus: moon of Saturn
“Enceladus has a hot rocky core, just like Earth, but it’s got huge ocean of salty water that’s capped with ice,” said Starkey. That ice cap is, effectively, its crust, which salty water erupts through from the ocean underneath as geysers—but not like those found on Earth, which are related to volcanic activity, but are not produced by a volcano.
“On Enceladus, these geysers or plumes are literally that body’s magma coming out of the inside,” said Starkey.
Titan: moon of Saturn
Saturn’s largest moon has rain and flash floods, lakes and oceans, an atmosphere and humidity. It’s got ice comprised not of water, but of liquid ethane and methane. Titan is the most similar place in the Solar System to Earth despite its chemistry being very different. But volcanoes?
“It’s definitely got volcanoes, which are probably releasing methane, and it could also have a subsurface ocean where heat meets salty water,” said Starkey. Microbes? It’s possible. “That’s exactly how we think life started on Earth,” said Starkey. “Titan is certainly an active world—and that’s what we’re looking for.”
Miranda and Titania: moons of Uranus
The smallest and innermost of Uranus and the the eighth largest moon in the Solar System, respectively, are something of a volcanic enigma. Miranda was passed by NASA’s Voyager 2 spacecraft in 1986. “These two look like evil worlds from a sci-fi movie, but they’re very geologically interesting,” said Starkey. “We don’t know much about these icy worlds and we need to go back.”
Miranda (which has a canyon 12 miles deep) is about half ice and half rock, with terraced layers that indicate both older and new surfaces coexisting. One theory is that partly melted ice is forced upwards to create new surfaces. Titania also has canyons and there’s some evidence for both tectonic activity and ice volcanoes.
It’s reckoned that Miranda, Titania and three other moons of Uranus—Ariel, Umbriel and Oberon—could have, or did have, liquid water below their icy surfaces.
Triton: moon of Neptune
“Triton was the first outer Solar System world that we found to be cryo-volcanically active,” said Starkey. Most of what we know about Triton came from a flyby in 1089 by Voyager 2, the spacecraft’s final target in its mission. “We saw streaks and plumes across the surface that looks like little fires burning—some kind of plume or volcanic activity but we have a lot of questions about Triton,” said Starkey. “It’s probably a captured moon and it’s probably being pulled and pushed about by Neptune.” Cue tidal heating as found on Io at Jupiter … but with an ocean, too.
Triton was identified as the highest priority candidate ocean world in January’s paper “The NASA Roadmap to Ocean Worlds”.
Pluto: dwarf planet in the Kuiper Belt
Triton is known as Pluto’s twin, so it’s no surprise that everyone’s favourite ex-planet may also be home to cry-volcanic activity. How do we know? New Horizons’ flyby in 2015 showed us a smooth surface with no craters and detected ammonia, which lowers the temperature that ice water melts and creates a sludge—a kind of lava.
It also found what could be an ice volcano called Wright Mons, which could be the largest volcano discovered in the outer Solar System. It’s home to only one impact crater.
Wishing you clear skies and wide eyes.