Old data show new evidence for Venusian volcanism

There are volcanoes on Venus, more than any other planet in the solar system. A lot of what’s known about the planet’s volcanism comes from NASA’s Magellan spacecraft, which orbited Venus and collected surface images with synthetic aperture radar from 1990 to 1992. The mission’s first three orbits focused on the Venusian surface, and the orbital paths allowed for a few locations to be imaged multiple times. But despite Magellan and subsequent uncrewed expeditions to Venus, researchers don’t know whether any of those volcanoes are active.

Searching for noteworthy geological features in the Magellan image library has been impractical because of the different angles at which the images were taken. But with software advances akin to Google Earth over the past decade, a viewer can now easily pan and zoom through mosaics composed of hundreds of images.

Robert Herrick (University of Alaska Fairbanks) and Scott Hensley (NASA Jet Propulsion Laboratory) used that kind of software to review Magellan images. Their search focused on a previously identified volcanic vent. They find that the vent may be active, on the basis of a change in its shape that must have occurred sometime during the eight months between when a pair of images were taken.

Even with the updated software, Herrick and Hensley couldn’t sift through the images in the Magellan database with a simple, automated image-analysis algorithm. Instead, they had to look through the images one by one. When they found what looked like a change in a relevant geologic feature between two images, they applied a stereo radargrammetry technique. In simple terms, it exploits the difference in the relative position of topographical features in each image to derive their actual height.

The pair of images shown below—from the north side of the Maat Mons shield volcano—appear to show modern volcanic activity. The first image, from Magellan‘s first mapping cycle, shows a circular, steep-walled vent on the volcano, at the lower center of the image. In the second image, the vent has expanded to an irregular shape and appears to have been made more shallow by lava partially filling it. The researchers also identified possible new volcanic flows—the region bounded by the dashed yellow line—north of the expanded vent.

The finding of just one changed geologic feature doesn’t say much about how common modern volcanism is on the surface of Venus. But if the planet has active volcanoes that modify the surface, it could mean that the average surface age is as young as a few tens of millions of years, rather than a few hundred million years according to an estimate based on the number of impact craters. Determining a definitive age for the surface of Venus would require more evidence. Herrick and Hensley estimate that their search of the Magellan data accounts for just 1.5% of the planet’s surface. (R. R. Herrick, S. Hensley, Science 379, 1205, 2023 .)