Venus volcanic activity tracked in Magellan radar images

Venus is a burning inferno. The surface temperatures are high enough to melt lead. Its surface pressure, 75 times that of Earth at sea level, is enough to crush even the most hardened metal objects. Sulfuric acid rain falls from noxious clouds in the atmosphere choking even the tiniest glimpse of the sky.

You would expect lava in a typical hellish landscape, but that element seems to be missing on Venus today. Astronomers are sure that our twin planet has had volcanic activity in the past, but they’ve never agreed on whether volcanoes still erupt and reshape Venus’s surface like 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 of the University of Alaska Fairbanks and Scott Hensley of 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 now await future missions to continue the volcano hunt.

“This [study] is the first-ever reported evidence of active volcanism on another planet,” said Darby Dyar, an astronomer at Mount Holyoke College in Massachusetts who was not an author of the paper.

The dense Venusian clouds would hide any volcanic activity from a spacecraft in orbit. Specially sharpened instruments can certainly dig beneath the clouds, but the planet’s erratic weather tends to shorten the life of probes to fully explore the terrain. Of the Soviet Venera landers of the 1960s, 1970s and 1980s, none survived more than about two hours.

[Related: The hellish Venus surface in 5 vintage photos]

Magellan changed that. Launched in 1989 and equipped with the best radar technology of its time had to offer, Magellan mapped much of Venus with the resolution of a city block. In the probe’s maps, scientists found evidence of giant volcanoes, past lava flows and lava-built domes — but no smoking gun (or smoking caldera) of living volcanic activity.

Before NASA crashed it into Venus’s atmosphere, Magellan made three different passes mapping the planet between 1990 and 1993, each time covering a different part. In doing so, 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 could find that out by comparing different radar images and spotting the difference.

But researchers in the early 1990s didn’t have the sophisticated image analysis software and tools that their counterparts have today. Back then, if they wanted to compare Magellan’s maps, they would have had to do it manually and compare the prints 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 distinguish actual changes from, say, shadows.

“To detect changes on the surface, we need a pretty big event, something that roughly disrupts more than a square kilometer of area,” says Hensley.

Finally, Herrick and Hensley found their smoking gun: an opening, just over a mile wide, on a formerly known mountain called Maat Mons. Between a Magellan radar image taken in February 1991 and another image taken about eight months later, this vent appeared to have changed shape, with lava seeping into nearby slopes.

As a check, Herrick and Hensley constructed simulations of volcanic vents based on the shape of the feature Magellan had seen. Their results matched what Magellan saw: a potential volcano in the process of belching lava onto the surface of Venus.

There is other evidence supporting their radical results. In 2012, ESA’s Venus Express mission detected a spike in sulfur dioxide in the planet’s atmosphere, which some scientists attribute to volcanic eruptions. In 2020, geologists identified 37 spots where magma plumes from the Venusian mantle could still touch the surface. But the evidence so far is circumstantial and astronomers have never seen a volcano in action on the “Morning Star.”

Fortunately for Venus enthusiasts, there may soon be heaps of new data to play with. The VERITAS space probe, part of NASA’s Magellan successor, was originally slated for a 2028 launch, but is now being pushed back to the early 2030s due to funding issues. When it finally reaches Venus, volcanoes will be near the top of the list of sights.

‘We’ll search [volcanoes] in two different ways,” said Dyar, who is also a deputy principal investigator at VERITAS. The spacecraft will perform multiple flybys to remap the entire surface of Venus, with a radar that has 100 times the resolution of Magellan’s instruments (like zooming in from a city block to a single building). As volcanoes erupt all over the planet, VERITAS can help scientists discover the changes they are etching into the landscape.

[Related: These scientists spent decades pushing NASA to go back to Venus]

In addition, VERITAS will probe Venus’ atmosphere for fluids, which scientists call volatiles, that volcanoes emit when they erupt. For example, water vapor is one of the most prominent volcanic volatiles. The phosphines that sparked 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 to arrive at Earth’s infernal twin in the next decade. The European Space Agency’s EnVision – scheduled for a launch in 2031 – will map the planet, just like VERITAS, only at an even higher resolution.

VERITAS and EnVision “will be much, much better able to see changes over time in different ways during their missions,” says Herrick, who is also involved in both missions. Not only will the two produce multiple higher-resolution scans for scientists to compare, the results can also be confirmed with Magellan’s antique maps, which will be 40 years into the past by the time they arrive.

“If we get high-resolution images,” says Dyar, “I think we’ll find active volcanism all over Venus.”

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