When scientists recently took a closer look at archival images of the surface of Venus, they discovered something new: evidence of volcanic activity on Earth's "twin."
The NASA Magellan spacecraft captured the images in the early 1990s as it circled our closest planetary neighbor, which is similar in size and composition to Earth.
A new analysis of the orbiter's perspective of a region near the Venusian equator reveals a volcanic vent that changed shape and increased greatly in size over the span of eight months.
The images of the vent represent the first direct geological evidence of recent volcanic activity on the surface of Venus, according to the researchers. A study detailing the findings was published Wednesday in the journal Science, and it was presented at the 54th Lunar and Planetary Science Conference in The Woodlands, Texas.
The Magellan mission became the first one to image the entire surface of Venus before the spacecraft intentionally plunged into the planet's hot, toxic atmosphere in 1994 to collect a final set of data. But a fleet of new missions will head for Venus within a decade, including VERITAS, the Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy mission.
The orbiter will use its instruments to uncover the secrets behind why a planet similar in size to Earth became covered in volcanic plains and topped with an inhospitable atmosphere.
"NASA's selection of the VERITAS mission inspired me to look for recent volcanic activity in Magellan data," said lead study author Robert Herrick, a research professor at the University of Alaska Fairbanks and member of the VERITAS science team, 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."
Herrick spotted the changes in images of Atla Regio, a vast highland region home to two of Venus' largest volcanoes, called Ozza Mons and Maat Mons. Both are similar to Earth's largest volcanoes, but because they have lower slopes, the two Venusian volcanoes are more spread out, Herrick said.
He noticed that a volcanic vent on the north side of a domed volcano that was part of Maat Mons changed between February and October 1991.
Magellan's image of the vent from February showed a circular vent spanning less than 1 square mile (2.2 square kilometers) with steep interior sides and areas of drained lava on the slopes.
Eight months later, the spacecraft captured another image showcasing a drastically different vent that appeared misshapen, had nearly doubled in size and was filled nearly to the rim with a lava lake.
Although the differences sound obvious, both images were taken from opposite angles and perspectives and at much lower resolution than images taken by the cameras included on spacecraft today.
Herrick worked with Scott Hensley, project scientist for VERITAS at NASA's Jet Propulsion Laboratory in Pasadena, California, to create computer models of the vent to determine what might have caused the 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," Hensley said. "While this is just one data point for an entire planet, it confirms there is modern geological activity."
The researchers believe the lava flow that Magellan witnessed in 1991 was similar to what was released by the 2018 Kilauea eruption in Hawaii.
"This was a needle-in-a-haystack search with no guarantee that the needle exists," Herrick said. "Finding a change that could be clearly confirmed as real was absolutely a surprise. We were pretty certain that Venus is volcanically active, but we didn't know if eruptions occur every few months, years, once every 10,000 years, or longer. All options could have fit with existing data. Unless we got incredibly lucky, we now know the frequency is every few months or so, similar to the family of Earth's big basaltic intraplate volcanoes like Hawaii, the Galapagos Islands, Canary Islands, etc."
While it's possible that a quake might have triggered the collapse of the volcanic vent's walls, the researchers believe such activity would have also caused a volcanic eruption.
Volcanoes act like windows into a planet's interior, allowing scientists to understand more about what factors influence its ability to be a habitable world. Missions such as VERITAS will help scientists gain a better understanding of Venus, just as Magellan did decades ago.
The new mission will be outfitted with radar to create global 3D maps of Venus and capture details about its surface composition, gravitational field and what unfolded in the planet's past.
"Venus is an enigmatic world, and Magellan teased so many possibilities," said Jennifer Whitten, associate deputy principal investigator of VERITAS and assistant professor of Earth and environmental sciences at Tulane University in New Orleans, in a 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."
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