Volcanic activity on Venus tracked in Magellan radar images

Venus is a fiery hell. 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 most durable metal objects. Sulfuric acid rain falls from noxious clouds in its atmosphere that drown out even the slightest glimpse of the sky.

In a typical hellscape, one would expect to find lava — but that element seems to be missing from Venus today. Astronomers are certain that our twin planet has had volcanic activity in the past, but they have never agreed whether volcanoes still erupt and reshape the surface of Venus as they do on Earth.

Now, two planetary scientists may have found the first evidence of an active volcano on Venus hidden in 30-year-old radar scans by NASA’s Magellan spacecraft. Robert Herrick of the University of Alaska Fairbanks and Scott Hensley of NASA’s Jet Propulsion Laboratory published their discovery in the journal Science on March 15. The new analysis has excited planetary scientists, many of whom are now awaiting future missions to continue hunting the volcano.

“This [study] it’s the first evidence of active volcanism on another planet,” says Darby Dyar, an astronomer at Mount Holyoke College in Massachusetts, who was not an author on the paper.

The dense clouds of Venus would hide any volcanic activity from an orbiting spacecraft. Specially honed instruments can certainly dip below the clouds, but the planet’s capricious weather tends to make the lives of probes too short to fully explore the spaces. Of the Soviet Venera aircraft 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 could offer, Magellan mapped much of Venus with the resolution of a plot. In the probe’s maps, scientists found evidence of giant volcanoes, past lava flows and domes made of lava — but no smoking gun (or smoking caldera) of live volcanic activity.

Before NASA’s crash into Venus’ atmosphere, Magellan made three separate passes mapping the planet between 1990 and 1993, covering a different part each time. In the process, the probe scanned about 40 percent of the planet more than once. If Venus’ terrain had shifted in the months between passes, scientists today could find it by comparing different radar images and spotting the difference.

But researchers in the early 1990s did not have the sophisticated software and image analysis tools that their counterparts have today. If they wanted to compare Magellan’s maps back then, they would have to do it manually, comparing prints with the naked eye. So Herrick and Hensley re-examined the Magellan data with more advanced computers. They found that in addition to blurriness, the detector often scanned the same feature from different angles, making it difficult to discern real changes other than, say, shadows.

“To detect surface changes, we need a fairly large event, something that disturbs roughly more than a square kilometer of area,” says Hensley.

Finally, Herrick and Hensley found their smoking gun: a vent, just over a mile wide, in 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 pouring onto nearby slopes.

To double check, Herrick and Hensley built simulations of volcanic vents based on the shape of the feature Magellan had spotted. Their results matched what Magellan saw: a possible volcano in the process of flowing lava onto the surface of Venus.

There is other evidence to support their radical results In 2012, ESA’s Venus Express mission detected a spike in sulfur dioxide in the planet’s atmosphere, which some scientists attributed to volcanic eruptions. In 2020, geologists identified 37 places where magma plumes from Venus’ mantle could still be touching its surface. But evidence has so far been sporadic, and astronomers have never actually seen a volcano in action on the Morning Star.

Fortunately for Venus fans, there may 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 launch in 2028, 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 attractions.

“We will search [volcanoes] in two different ways,” says Dyar, who is also deputy principal investigator at VERITAS. The spacecraft will make multiple flybys to remap the entire surface of Venus, with radar that has 100 times the resolution of Magellan’s instruments (such as zooming from a city block to a single building). If there are volcanoes erupting across the planet, VERITAS can help scientists spot the changes they’re carving into the landscape.

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

In addition, VERITAS will scan Venus’ atmosphere for liquids, which scientists call volatiles, that volcanoes spew as they erupt. Water vapor, for example, is one of the most important volcanic volatiles. The phosphines that sparked whispers of life on Venus in 2020 also fall into this class of molecules. (Indeed, some experts have tried to explain their presence through volcanoes).

VERITAS is not the only mission set to reach Earth’s infernal twin in the next decade. The European Space Agency’s EnVision — scheduled for launch in 2031 — will map the planet just like VERITAS, only at an even higher resolution.

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

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

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