Active volcanoes on Venus

It’s official: Volcanoes rumble on Venus! The surface of this telluric planet is dotted with many volcanoes, but so far there has been no indication that they are still active. It is now being done thanks to geophysicists Robert Herrick, of the University of Alaska in Fairbanks, and Scott Hensley, of the Jet Propulsion Laboratory, who re-analyzed images taken by the probe thirty years ago. Magellan. With this discovery, Venus becomes, after Earth and Io, the third body in the solar system to show volcanic activity.

The surface of Venus has more volcanoes than any other body in the solar system. It consists mainly of basalt, which indicates that volcanism played a major role in the history of the planet: researchers believe that its surface was almost completely renewed between 300 and 500 million years ago. But no active volcano was known until recently.

By 2010, signs of recent volcanic activity began to accumulate. Three hot spots are detected In data collected from the probe’s Virtis infrared instrument Venus Express, particularly at the level of Idon Mons volcano. In 2012, “we discovered a great deal of significance Differences in sulfur dioxide concentration above the clouds of Venus, ”says Emmanuel Marc, a researcher at the University of Versailles Saint-Quentin-en-Yvelines, in the origin of the discovery. Then, in 2014, Ephemeral bright spots have been detected in the Janice Chasma area by analyzing data from 2008. Finally, in 2015, at the adjacent Janice Chasma Trench, A local increase in temperature has been demonstrated.

But none of these clues completely convinced researchers of the existence of active volcanism on Venus. It is already difficult to directly observe the planet. Its atmosphere is made up mostly of carbon dioxide, a powerful greenhouse gas that blocks out much of the infrared radiation. Added to this are clouds of sulfuric acid, which reflect 75% of visible light.

In contrast, the atmosphere and clouds are transparent to radio waves. So it is possible to “see” the surface of Venus using radar. This is what the probe did Magellanwho surveyed Venus between 1990 and 1994. “Rough surfaces on radio wavelengths appear dull,” explains Emmanuel Marck, while smooth surfaces appear shiny. »

They are in these investigative archives Magellan Thirty-year-olds Robert Herrick and Scott Hensley were diving, searching for an area whose appearance would have changed between two segments of the probe. For this, they focused their efforts on the volcanic region of Atla Reggio, in the northern hemisphere of Venus. After hundreds of hours of searching with the naked eye! Magellan. This would be a sign of the current volcanic activity. Below this building also appeared what could be a lava flow.

But everything is not so simple. “ X-ray images are difficult to interpret. Depending on how the radar is pointed, the images from the same surface can be very different. Emmanuel Mark confirms. The researchers ran numerical simulations to ensure that these “geometric” effects did not explain the differences observed between the two radar images. Verdict: If not completely ruled out that a lava flow could be a coarseness-related artifact from the surface, Double the extent of the crater, for its part, is unmistakable. “It can only be explained by active volcanoes!” says Emmanuel Marc. So Venus is not a dead planet after all.