NASA’s Magellan spacecraft spent four years mapping Venus with radar, and what it found was unsettling: over 1,600 major volcanoes dotting a planet that’s basically Earth’s evil twin. That was back in the early 1990s, and we’re still parsing what it means.
When You Can’t Exactly Walk Up to the Volcano With a Thermometer
Here’s the thing about studying extraterrestrial volcanoes—you can’t just plant seismometers and wait. Mars’s Olympus Mons stands 21 kilometers tall, making it nearly three times the height of Mount Everest, and we’ve never felt it rumble. Not once. Because getting instruments onto another planet is hideously expensive, and keeping them alive is even harder.
So we improvise.
Planetary scientists have become masters of detective work, piecing together volcanic histories from orbital photographs, spectroscopy data, and mathematical models that would make your calculus teacher weep. When the Mars Reconnaissance Orbiter spotted relatively fresh lava flows on the flanks of Arsia Mons in 2017—flows that were only about 50 million years old—it rewrote our understanding of Martian geological timescales. Fifty million years is practically yesterday in geological terms, suggesting Mars might not be the dead world we assumed.
Turns out, studying volcanoes on other planets is less about watching eruptions and more about reading epitaphs.
The Galileo spacecraft flew past Jupiter’s moon Io in 1996 and caught something extraordinary: active volcanic plumes shooting 300 kilometers into space. Io has somewhere around 400 active volcanoes, making it the most volcanically active body in the solar system, and it’s all because Jupiter’s gravity is literally kneading the moon like dough, generating enough friction to melt its insides. That’s tidal heating, and it’s as violent as it sounds.
The Weird Chemistry of Volcanoes That Don’t Erupt Rock
Wait—maybe calling them all “volcanoes” is the first mistake. Saturn’s moon Enceladus shoots geysers of water ice from its south pole, fountains that spray hundreds of kilometers high. The Cassini spacecraft flew through these plumes between 2005 and 2017, tasting their chemistry (yes, spacecraft can taste), and found organic molecules, salt, and silica particles. These aren’t lava flows; they’re cryovolcanic, erupting substances that would be frozen solid on Earth.
Neptune’s moon Triton probably has nitrogen geysers. Nitrogen! We detected dark streaks on its surface during Voyager 2’s flyby in 1989, likely caused by subsurface nitrogen erupting through ice, carrying dark material with it. The whole concept breaks your brain a little—imagining a geyser made of something that’s already a gas at room temperature on Earth.
The chemistry gets weirder the farther out you go.
Reading Volcanic Tea Leaves From Millions of Kilometers Away
Spectroscopy is the secret weapon here. Different materials absorb and reflect light at specific wavelengths, creating distinctive signatures that instruments can detect from orbit. When scientists analyzed data from the VIRTIS instrument on ESA’s Venus Express mission, they found infrared hotspots on Venus’s surface that fluctuated between 2008 and 2013, suggesting recent volcanic activity. Not ancient flows—recent ones, as in possibly still happening.
The technique works like this: you point a spectrometer at a planetary surface, collect the light bouncing back, split it into its component wavelenghts, and look for the fingerprints of specific minerals or gases. Fresh basalt looks different from weathered basalt. Sulfur dioxide concentrations spike when volcanoes erupt. It’s forensics at planetary scale.
But here’s where it gets frustrating: we’re making educated guesses based on incomplete data. Mars has deposits of olivine, a mineral that weathers quickly in water, sitting exposed on the surface in places like Nili Fossae. That tells us those regions have been dry for a long time, which tells us something about when volcanic activity might have stopped bringing water to the surface through hydrothermal systems. See how many logical leaps that requires?
Sometimes the evidence is more direct. In 2013, scientists analyzing data from Mars’s InSight lander detected what appeared to be marsquakes originating from Cerberus Fossae, a region with relatively young volcanic features. The seismic activity suggested magma might still be moving underground, even if it’s not erupting anymore. That’s about as close as we get to catching a Martian volcano in the act.
The whole enterprise feels like trying to diagnose a patient through a keyhole while wearing oven mitts. Yet somehow, it works—slowly, expensively, but it works. We’ve mapped volcanic provinces on Mercury, Venus, Mars, and multiple moons, building a comparative planetology that helps us understand how rocky bodies evolve. Every new mission adds pixels to the picture, refining our models of how planets live and die through their volcanic phases.
And ocasionally, we get lucky enough to watch something actually explode in real-time, like when the New Horizons probe photographed active plumes on Io during its 2007 Jupiter flyby, catching Tvashtar volcano mid-eruption with a plume reaching 330 kilometers high.
