A volcanic vent on Venus that changed shape over a period of eight months is the first direct evidence that our neighbouring planet is volcanically active.

Venus has many prominent volcanic features, such as vents and the dry beds of lava lakes, but it was unclear whether these were remnants of a distant volcanic past or signs of current activity.

Between 1990 and 1994, NASA’s Magellan satellite used radar to map Venus’s surface in detail, including its volcanic features. Until recently, however, computers were ill-equipped to properly analyse the vast amount of data it generated.

The way in which Magellan mapped Venus’s surface, taking photos every eight months at different viewing angles, also made it impossible to automatically search for changes in surface features. The only way to identify differences was to look through the images by eye.

“The daunting aspect of this is it’s a needle-in-a-haystack search, where there’s no guarantee that the needle exists,” says Robert Herrick at the University of Alaska Fairbanks, who, along with Scott Hensley at NASA’s Jet Propulsion Laboratory in California, presented the findings at the Lunar and Planetary Science Conference in Houston, Texas, on 15 March.

By combing through areas of Venus’s surface in which they thought volcanic activity was more likely, the pair found the vent, which is in the Maat Mons volcano system, home to the planet’s highest volcano.

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Between February and October 1991, the vent changed from a circular, 2-square-kilometre hole to a more shallow, irregular hole with an area almost twice as big. In the later images, there were also features downhill from the vent that looked like active lava flows, but the images weren’t clear enough to fully make them out. “A reasonable interpretation is that a lava lake formed over those eight months, and that volcanism occurred downhill,” says Herrick.

While the finding validates many predictions and hypotheses about active volcanism on Venus, it tells us little about the frequency of volcanic eruptions on the planet because it is the only sample we have – but the fact that we saw it at all could tell us something.

“There’s the possibility that we observed the only thing that’s happened on Venus in the last 1000 years and got incredibly lucky, but the odds are that if we saw something change over a short, eight-month period, then at least volcanic eruptions occur on Venus at a similar sort of level to the intraplate volcanism on Earth, in the every-few-months time frame,” says Herrick.

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“We know Venus must be active, but demonstrating it from Magellan data has, until now, proven elusive,” says Philippa Mason at Imperial College London.

Confirming that Venus is volcanically active is especially useful given upcoming missions to Venus, says Mason, such as the European Space Agency’s EnVision and NASA’s VERITAS satellites. These missions will use radar – like Magellan did, but in a more advanced form – to map the planet’s surface and interior, as well as spectroscopy to analyse gases in its atmosphere. These methods will teach us more about the extent and nature of Venus’s volcanism.

Journal reference:

Science DOI: 10.1126/science.abm7735