Evidence of active volcanoes—finally

Venus: Evidence of Active Volcanoes—Finally

Perspective view across Ma’at Mons on Venus, based on Magellan’s radar data. credit: NASA/JPL

Venus is roughly the same size, mass, and density as Earth. Therefore it must generate heat in its interior (by the decay of radioactive elements) at the same rate as that of the Earth. On Earth, one of the main ways this heat escapes is through volcanic eruptions. During an average year, at least 50 volcanoes erupt.

But despite decades of searching, we haven’t seen clear signs of volcanic eruptions on Venus — until now. A new study of the geophysicist Robert Herrick from the University of Alaska, Fairbanks, which he reported this week at the Planetary and Lunar Science Conference in Houston and Published in the journal Scienceshas finally caught one of the planet’s volcanoes red-handed.

The surface of Venus is not easy to study because it has a dense atmosphere including an unbroken cloud layer at an altitude of 45-65 kilometers and is opaque to most wavelengths of radiation, including visible light. The only way to get a detailed view of the Earth from above the clouds is with radar pointing down from an orbiting spacecraft.

A technique known as aperture superimposition is used to create an image of a surface. This combines the variable power of radar echoes returned from the ground – incl time delay between transmitting and receiving, as well as slight frequency shifts corresponding to whether the spacecraft is approaching or moving away from a particular echo origin. The resulting image looks somewhat like a black and white photograph, except that brighter areas usually correspond to rough surfaces, and darker areas to smoother surfaces.

Venus: Evidence of Active Volcanoes—Finally

Venus seen in ultraviolet light by the Japanese spacecraft Akatsuki in December 2016. The surface cannot be seen. Credit: ISAS/JAXA

NASA’s Magellan probe orbited Venus from August 1990 to October 1994 and used this type of radar technology to map the planet’s surface with a spatial resolution of about a hundred meters at best. Show that more than 80% of the surface is covered lava flowbut how the youngest of them recently exploded, and whether any eruptions continue today, remained a mystery for the next three decades.

it was there Various hints of activity Provided by spacecraft that peer into and sometimes through the clouds—suggesting that the rocks there are so young that their minerals have not yet been altered by interaction with the acidic atmosphere, and thus the lava has been freshly erupted. Thermal anomalies that could correspond to active pyroclastic flows, temporary local hiccups have also been detected in The concentration of sulfur dioxide in the atmosphere—another possible sign of volcanic eruptions. But none of these things were entirely convincing.

Spotted a volcanic vent

Venus: Evidence of Active Volcanoes—Finally

A 140-km-wide Magellan radar image of Venus shows pyroclastic flows (bright because they are jagged) that have begun to encroach on an ancient impact crater. Credit: NASA/JPL

Now the new study seems to have settled the matter, by revealing changes to the surface that must really be the result of volcanic activity. The authors spent hundreds of hours comparing Magellan’s radar images of parts of Venus that had been imaged more than once, looking for new or changed features on the surface.

They focused on promising volcanic regions, and eventually discovered an example in which the details of the image recorded in October 1991 differed from those on an image from February of the same year. The changes they saw are best explained by a volcanic eruption during that time window.

Using radar images to verify surface changes is challenging because the appearance of an unchanging surface can vary depending on the surface slopes and direction of view. However, the researchers ran simulations to verify that the observed changes could not be caused by these objects.

Venus: Evidence of Active Volcanoes—Finally

Close-ups of the active volcanic vent north of the summit of Maat Mons in February and October 1991. Between these two dates, the vent widened and changed shape, and new lava flows seemed to appear. Credit: NASA/JPL

The twin images show an initially circular crater about 1.5 kilometers across that between February and October doubled in size by expanding eastward. It also became shallow, and the authors suggest that the crater is a partially collapsed volcanic vent that largely filled with fresh lava during October.

New lava flows extending several kilometers downhill, north of the crater, are also likely, which either flooded over the crater rim or seeped from the associated fissure. The active crater is located high above Maat Mons, one of the largest volcanoes on Venus whose summit rises 5 kilometers above the surrounding plains.

future missions

Most planetary scientists had already predicted Venus to be volcanically active. The focus of attention will now certainly shift to how often and in what number of locations volcanic eruptions occur on Venus. The biggest surprise in all of this was that it took so long for someone to find the evidence Surface Changes that have been dormant in Magellan’s data for 30 years.

Venus: Evidence of Active Volcanoes—Finally

Maat Mons. The arrow indicates the location of the volcanic vent that erupted in 1991, which is too small to appear at this scale. Credit: NASA/JPL

The prospect of finding and studying ongoing volcanic activity is one of the main motivations for NASA Truth, honesty Mission and Jesus Imagine Mission (both approved in 2021). Each would carry better imaging radar than Magellan. EnVision aims to reach orbit around Venus in 2034. Originally Veritas was supposed to be around several years ago, but there was delays in the schedule.

with NASA Da Vinci With the mission likely arriving a year or two earlier, and providing visual images from below the clouds as it descends, we’re in for an exciting time about ten years from now.

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