by Spying on erupting volcanoes on Venus has dreamed of scientists for half a century. This unfathomably hot world is shrouded in toxic clouds, but previous missions have shown the surface is covered with volcanic features. And now, thanks to recorded memories of a long-dead spacecraft, scientists have struck scientific gold: they’ve seen a vent on Venus change shape, expand, and appear to overflow with molten rock.
“My bet is that a lava lake erupted,” says Robert Herrick, a planetary scientist at the University of Alaska Fairbanks and one of the two co-authors of the new study.
As reported today in the Journal ScienceHerrick and a colleague spotted the volcanic chasm — on the side of the colossal Maat Mons volcano — in radar images taken by NASA’s Magellan spacecraft in 1991.
“It’s some of the most compelling evidence we’ve seen,” says Stephen Kane, a planetary astrophysicist at the University of California, Riverside, who was not involved in the work.
The results have stunned the scientific community. Experts expected to find erupting volcanoes on Venus, but not until two spacecraft carrying cutting-edge, cloud-penetrating radar systems — NASA’s VERITAS and Europa’s EnVision — arrive sometime in the early 2030s.
Evidence of ongoing volcanic activity on Venus has existential implications. The planet is very similar to Earth in size and composition, but its considerable ancient water supplies – possibly in the form of oceans – were long ago evaporated when the planet was scorched during a mysterious cataclysm. Runaway climate change triggered by apocalyptic eruptions remains the prime suspect. By understanding Venus’s volcanism today, scientists can learn more about the divergent fates of Earth and its glowing sister world.
“If you want to understand the only other Earth-sized world we’ll ever reach anywhere in the universe, Venus is the only choice you have,” says Paul Byrne, a planetary scientist at Washington University in St. Louis, who doesn’t was part of the new study.
A hidden hellscape
Venus’ opaque atmosphere prevents its surface from being seen from Earth. Only a handful of spacecraft have taken in the landscape, either by plummeting through the clouds and surviving no more than an hour or two on the sweltering surface, or by circling the planet and peering through the clouds using technologies like radar.
A fleet of Soviet spacecraft revealed in the early 1980s that Venus was almost completely covered by volcanic structures – some Earth-like, some clearly extraterrestrial. NASA’s radar-equipped Magellan spacecraft arrived in 1990 hoping to map the planet’s features in unprecedented detail.
By repeatedly orbiting the planet and examining the same locations multiple times, scientists hoped to spot signs of volcanic activity. But there were complications. The low resolution of radar meant that any physical changes had to be large enough to show up in the images. And early in the mission, Magellan’s orbit began to deteriorate, causing the spacecraft to image less of the surface with each successive trip around the planet.
Despite these challenges, 43 percent of the planet has been mapped at least twice. But comparing multiple images of the same volcano to look for changes also proved problematic, as the angle of each image often differed between orbits.
In the decades following the mission, no one succeeded in finding a convulsive volcano.
A transforming volcanic chasm
Scientists have found much indirect evidence of active volcanism on Venus, including spikes in atmospheric gases associated with volcanic burps, suspiciously juvenile mineral specks, and unusual features on colossal circular structures called coronae that suggest underlying magmatic turbulence.
“We always seem to be teased by this indirect evidence,” says Kane. But the holy grail—a belching volcano or a flowing river of molten rock—remained elusive.
In 2021, EnVision and VERITAS were selected for launch, becoming the best choices to find active volcanism on Venus. But Herrick remained impatient.
“I’ve had a lot of Zoom meetings where I didn’t have to fully engage,” he says, referring to the peak of the pandemic. “Whenever I had an hour here or there, I just started” looking at the old Magellan data. He manually lined up images of Venus’ volcanoes, looking for anything unusual.
During a search Herrick Maat examined Mons forensically. Named after the Egyptian goddess of truth and justice, it is the tallest volcano on earth – and something changed on one of its flanks between February and October 1991. In those eight months, matter appears to have flooded into an open vent that grew from 0.8 to 1.5 square miles, and a fresh stream of material appeared to seep down the slope.
“I think that’s really something,” Herrick recalls. He directed it from his co-author Scott Hensely of NASA’s Jet Propulsion Laboratory, who agreed: Something volcanic had moved.
The substance filling the vent could be rocky debris from a landslide. It’s also possible that the stream-like feature was already present in the February images but could not be seen due to the angle of the images.
But the most likely scenario is that in 1991 a huge lava eruption filled the expanding vent and some of it overflowed the rim or bled through a fissure. “We can definitely say that it has changed shape,” says Herrick. And when a volcano on Earth changes shape so dramatically, the cause is always molten rock.
In search of the heartbeat of Venus
After so much circumstantial evidence, “For the first time, we’re seeing a change in something,” says Anna Gülcher, a planetary scientist at the California Institute of Technology who wasn’t involved in the work.
“I think what they saw is real,” says Byrne of Washington University. He suspects that the change in the vent may be more due to subterranean movements, such as e.g. B. Magma moving violently underground than an eruption.
Scientists hope to answer a fundamental question: “What’s the planet’s daily volcanic heartbeat doing?” asks Byrne.
The volcanoes of Earth and Jupiter’s moon Io keep erupting. Mars could erupt once every few million years. Where does Venus fall on this spectrum?
The discovery suggests the planet looks more like vigorous, Earth-like volcanism. VERITAS and EnVision will answer that question, but until then, this study will encourage scientists to study Magellan’s records in hopes of finding another erupting Venusian volcano.
