Venus is a searing inferno. Its surface temperatures are hot enough to melt lead. Its surface pressures, 75 times that of Earth at sea level, are enough to crush even the hardiest of metal objects. Sulfuric acid rain falls from noxious clouds in its atmosphere that choke out even the slightest glimpse of the sky.
In a typical infernal hellscape, you’d expect to find lava—but that element seems to be missing from Venus today. Astronomers are sure that our twin planet had volcanic activity in the past, but they’ve never agreed if volcanoes still erupt and reshape the Venusian surface as they do Earth’s.
Now, two planetary scientists may have found the first evidence of an active Venusian volcano hiding in 30-year-old radar scans from NASA’s Magellan spacecraft. Robert Herrick from the University of Alaska Fairbanks and Scott Hensley from NASA’s Jet Propulsion Laboratory published their breakthrough in the journal Science on March 15. The new analysis has excited planetary scientists, many of whom are now waiting for future missions to carry on the volcano hunt.
“This [study] is the first-ever reported evidence for active volcanism on another planet,” says Darby Dyar, an astronomer at Mount Holyoke College in Massachusetts, who wasn’t an author on the paper.
The dense Venusian clouds would hide any volcanic activity from a spacecraft in orbit. Specially honed instruments can certainly delve under the clouds, but the planet’s capricious weather tends to make probes’ lives too short to fully explore the grounds. Of the Soviet Venera landers of the 1960s, 1970s, and 1980s, none survived longer than around two hours.
Magellan changed that. Launched in 1989 and equipped with the finest radar that the technology of its time could offer, Magellan mapped much of Venus to the resolution of a city block. In the probe’s charts, scientists found evidence of giant volcanoes, past lava flows, and lava-built domes—but no smoking gun (or smoking caldera) of live volcanic activity.
Before NASA crashed it into the Venusian atmosphere, Magellan made three different passes at mapping the planet between 1990 and 1993, covering a different chunk each time. In the process, the probe scanned about 40 percent of the planet more than once. If the Venusian terrain had shifted in the months between passes, scientists today might find it by comparing different radar images and spotting the difference.
But researchers in the early 1990s didn’t have the sophisticated software and image-analysis tools that their counterparts have today. If they wanted to compare Magellan’s maps then, they’d have had to do it manually, comparing printouts with the naked eye. So, Herrick and Hensley revisited Magellan’s data with more advanced computers. They found that in addition to blurriness, the probe often scanned the same feature from different angles, making it difficult to tell actual changes apart from, say, shadows.
“To detect changes on the surface, we need a pretty big event, something that disturbs roughly more than a square kilometer of area,” Hensley says.
Eventually, Herrick and Hensley found their smoking gun: a vent, just more than a mile wide, on a previously known mountain named Maat Mons. Between a Magellan radar image taken in February 1991 and another taken about eight months later, this vent appeared to have changed shape, with lava oozing out onto the nearby slopes.
To double-check, Herrick and Hensley constructed simulations of volcanic vents based on the shape of the feature that Magellan had spotted. Their results matched what Magellan saw: a potential volcano in the process of burping lava out onto Venus’s surface.
There is other evidence that backs up their radical results In 2012, ESA’s Venus Express mission spotted a spike in sulfur dioxide in the planet’s atmosphere, which some scientists ascribe to volcanic eruptions. In 2020, geologists identified 37 spots where magma plumes from the Venusian mantle might still touch its surface. But the evidence has so far been circumstantial, and astronomers have never actually seen a volcano in action on the “Morning Star.”
Fortunately for Venus enthusiasts, there might soon be heaps of fresh data to play with. The VERITAS space probe, part of NASA’s follow-up to Magellan, was originally scheduled for a 2028 launch, but is now pushed back to the early 2030s due to funding issues. When it does finally reach Venus, volcanoes will be near the top of its sightseeing list.
“We’ll be looking for [volcanoes] in two different ways,” says Dyar, who is also deputy principal investigator on VERITAS. The spacecraft will conduct multiple flybys to map the entire Venusian surface again, with radar that has 100 times the resolution of Magellan’s instruments (like zooming in from a city block to a single building). If there are volcanoes erupting across the planet, VERITAS might help scientists spot the changes that they etch into the landscape.
Additionally, VERITAS will examine the Venusian atmosphere in search of fluids, which scientists call volatiles, that volcanoes belch out as they erupt. Water vapor, for example, is one of the most prominent volcanic volatiles. The phosphines that elicited whispers about life on Venus in 2020 also fall into this category of molecules. (Indeed, some experts tried to explain their presence via volcanoes).
VERITAS isn’t the only mission set to arrive at Earth’s infernal twin in the next decade. The European Space Agency’s EnVision—scheduled for a 2031 launch—will map the planet just like VERITAS, only with even higher resolution.
VERITAS and EnVision “will have far, far better capability to see changes with time in a variety of ways during their missions,” says Herrick, who is also involved with both missions. Not only will the two produce multiple higher-resolution scans for scientists to compare against each other, the results can also be corroborated with Magellan’s antique maps, which will be 40 years in the past by the time they arrive.
“When we get high-resolution imagery,” Dyar says, “I think that we’re going to find active volcanism all over Venus.”