Venus – planet earth's planetary next-door neighbor – may seem peaceful in photos, yet a fresh analysis of radar images obtained over three decades ago has yielded new evidence indicating that the second planet from the Sun is currently volcanically active, hosting a dynamic world with eruptions and lava flows.
Researchers said radar images taken by NASA's Magellan spacecraft showed that a volcanic vent about 1.6 kilometers (1 mile) wide on the Venusian surface expanded and changed shape over an eight-month span in 1991. The vent is situated on Maat Mons, which at about nine kilometers tall, and is the planet's highest volcano and second-highest mountain.
A February 1991 image showed the vent as a circular formation covering about 2.6 square kilometers (1 square mile). An image from October 1991 showed the vent with an irregular shape covering about 3.9 square kilometers.
"What we definitively can demonstrate is that a volcanic vent got larger and looks to have gone from conical and hundreds of meters deep in its interior to a flat, nearly filled interior," said Prof. Robert Herrick, a University of Alaska Fairbanks Geophysical Institute research professor and lead author of the study published in the journal Science.
"Our interpretation is that there is a new influx of magma into a chamber underneath the vent, and that results in the formation of a broader, irregular caldera (a large depression created when a volcano erupts and collapses) that still has an active lava lake in it when the second image was taken," professor Herrick said.
The vent is located on the northern side of a larger volcanic structure just off the main summit of Maat Mons.
"Although it is possible, the vent collapse was not associated with active volcanism, on Earth this large a collapse is usually associated with some sort of magmatic movement, and hence we think it is likely to be the case here," said study co-author Scott Hensley, a senior research scientist specializing in radar remote sensing at NASA's Jet Propulsion Laboratory in California.
Venus is covered with craters, volcanoes, mountains and lava plains. Magellan imaged portions of Venus up to three times spanning 24 months from 1990 to 1992. Advances in computing capability have made analyzing this data easier in recent years.
The new findings suggest there are eruptions on Venus about every few months, similar to some Earth volcanoes in places like Hawaii, the Canary Islands and Iceland, Herrick said.
This is the latest evidence that Venus, lacking the plate tectonics that gradually reshapes Earth's surface, is not the geologically dormant world some scientists had once considered it to be. Another study published in 2020 identified 37 volcanic structures apparently active in the past 2-3 million years.
Venus, with a diameter of about 12,000 kilometers, is slightly smaller than Earth. Its thick atmosphere – mainly carbon dioxide – traps in heat in a runaway greenhouse effect, rendering Venus the solar system's hottest planet.
In our solar system, earth resides comfortably within the "habitable zone" around the sun – the distance considered not too close and not too far from a star to be able to host life, with Venus near the inner boundary and Mars close to the outer edge.
"As we continue to discover new solar systems around other stars, understanding how Venus and Earth came to end up so different now is important to understanding what the conditions are for making a planet habitable," professor Herrick said.
"For instance, there are a lot of scientists who think Venus might have been habitable for a large fraction of its history, which would mean that the concept of a 'habitable zone' of a fixed distance around a star is an outdated concept. Maybe the distance is just one contributing factor and there is a bunch of other factors equally important," professor Herrick noted.