Planetary scientists have found groundbreaking evidence of recent volcanic activity on Venus. Archives from NASA's Magellan mission show telltale signs that Maat Mons, a 5-mile-high (8 kilometers) volcano on Earth's hellish twin, was active in 1991.

Magellan, launched in May 1989, was the first spacecraft to map the entire surface of Venus. The mission’s radar images revealed that Venus is peppered with volcanoes, but at the time scientists couldn't tell whether any of them were still active.

Now, a new analysis of these 30-year-old archives has detected a volcanic vent swelling with lava in the Atla Regio region, near the planet's equator.

The discovery was inspired by NASA's next mission to our sister planet, which will launch within a decade. VERITAS (Venus Emissivity, Radio science, InSAR, Topography And Spectroscopy) led by the agency's Jet Propulsion Laboratory in Southern California, will scan Venus from surface to core to understand how a rocky planet so similar to ours became a scorching hell-hole.

"NASA's selection of the VERITAS mission inspired me to look for recent volcanic activity in Magellan data," Robert Herrick, a research professor at the University of Alaska Fairbanks and member of the VERITAS team, who led the search of the archival data, said in a statement. "I didn't really expect to be successful, but after about 200 hours of manually comparing the images of different Magellan orbits, I saw two images of the same region taken eight months apart exhibiting telltale geological changes caused by an eruption."

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Researchers described the two images in a study, published Wednesday (March 15) in the journal Science. They also presented their results at the 54th Lunar and Planetary Science Conference in The Woodlands, Texas, on Wednesday.

Maat Mons is the tallest volcano on Venus, towering 26,250 feet (8,000 meters) above the barren volcanic plains and deformed terrain of the planet's surface. In a picture taken in February 1991, a volcanic vent associated with Maat Mons appears nearly circular, with signs of drained lava on its exterior slopes, and covers an area of less than 1 square mile (2.2 square kilometers). In October, Magellan captured the same vent brimming with a lake of bubbling lava; it was misshapen and had doubled in size.

But the orbiter photographed the vent from different orbits and with poor resolution, making it difficult for the scientists to compare the images. They managed to line them up manually, however, and build computer models of the vents, which helped them determine what caused the geological changes.

"Only a couple of the simulations matched the imagery, and the most likely scenario is that volcanic activity occurred on Venus' surface during Magellan's mission," Scott Hensley, a senior research scientist at NASA's Jet Propulsion Laboratory who worked on the Magellan radar mission, said in the statement. "While this is just one data point for an entire planet, it confirms there is modern geological activity."

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The gush of lava from Maat Mons’ crater would have been similar in size to the eruption of Hawaii's Kilauea volcano in 2018, the researchers said in the statement.

This finding gives scientists a taste of the discoveries NASA’s upcoming mission will likely reveal. VERITAS is the first spacecraft to return to Venus since the 1990s. Its mission is to create 3D models of the planet to reveal its innermost secrets.

"Venus is an enigmatic world, and Magellan teased so many possibilities," Jennifer Whitten, an assistant professor at Tulane University in New Orleans and a member of the VERITAS team, said in the statement. "Now that we're very sure the planet experienced a volcanic eruption only 30 years ago, this is a small preview for the incredible discoveries VERITAS will make."