Ancient images reveal volcanic eruption on Venus – 03/15/2023 – Science
It is true that these are low-resolution radar images produced by an old spacecraft more than 30 years ago. But a new look at them has revealed what may be the first evidence of ongoing volcanic activity on the surface of Venus.
The work was carried out by Robert Herrick of the University of Alaska at Fairbanks and Scott Hensley of NASA’s Jet Propulsion Laboratory, both in the US. The conclusions were presented during the 54th Lunar and Planetary Science Conference, in The Woodlands, Texas, and appear in an article to be published in this week’s edition of the journal Science.
The finding is important because it gives some guidelines to the strong existing discussion about the dynamics of Venusian volcanism and may even inform recent questions raised about the planet, such as the presence of phosphine in the upper atmosphere, a molecule that may (or may not) be evidence of life in the clouds of that world.
Venus is generally recognized as an Earth twin—more precisely as an “evil” twin. It’s our closest planetary neighbor, and it’s practically the same size and mass as Earth (just a tiny bit less). It is the solar world that receives the level of irradiation closest to the terrestrial one. And yet, there are marked differences.
Most notable for us living creatures is the ultra-dense atmosphere dominated by carbon dioxide, capable of generating such a powerful greenhouse effect that the surface temperature exceeds 460°C, comparable to that of a pizza oven. Nothing we mean by life can live there.
The upper atmosphere is more pleasant, with temperature and pressure similar to what we find on Earth at sea level, but still extremely dry. If there’s any chance of biology on Venus, it’s only in the clouds, and most scientists think that’s pretty unlikely anyway.
Another important contrast is rotation: while the Earth rotates around its own axis every 23h56min, Venus takes 243 days (more than the Venusian year itself, 224 days) to do the same thing.
In 1989, NASA launched the Magellan mission. Named after the navigator Fernão de Magalhães, who was the first to circumnavigate the Earth, it would circle Venus multiple times to map the neighboring planet as precisely as possible.
It is not a trivial challenge, since the Venusian surface is completely covered by dense clouds all the time. To collect the images, Magellan used radar, making many sweeps in narrow bands of the planet, until it covered the entire planet. The resolution wasn’t great: between 100 and 300 meters per pixel.
It was with these data, collected between 1990 and 1992, that the pair of researchers made their discovery. They pored over regions that were imaged at least twice by the spacecraft and that were likely to be more likely to exhibit volcanic activity, looking for differences between a “before” and an “after.”
The automated analysis of this material is counterproductive, because the change in the angle of observation in each of the images makes the work of the machine more difficult. The trained eye of a geologist is even more powerful.
And that’s how the duo found in Atla Regio, the region where the largest Venusian volcanoes are located, possible evidence of eruption in two images taken between February and October 1991.
Herrick and Hensley focused on a volcanic vent located near the large Maat Mons volcano, which appears to have expanded and changed shape in the nine months between one image and the next. “In the cycle 1 image, the chimney appears almost circular (1.5 x 1.8 km, area of 2.2 kmtwo), with steep inner slopes,” the two wrote. “In the cycle 2 image, the chimney got bigger (4 kmtwo) and irregularly shaped.”
Additionally, the researchers found another nearby region that appeared to contain new flows not apparent in the first image.
To make sure this wasn’t an illusion caused by the different angles at which the two images were produced, the pair conducted a computer simulation of how the image would change from angle to angle, based on the initial appearance of the chimney. With that, they found that it wasn’t really an optical illusion — the chimney seems to have changed shape.
As for the flows, it was not possible to make this corroboration by simulation. Still, scientists feel safe saying that there is evidence that an eruption took place between February and October 1991 and that the level of activity is comparable to what you see in, say, Hawaii.
THE VENUSIAN VOLCANISM DEBATE
It is not surprising that there are active volcanoes there. In contrast to Mars, a smaller planet that appears to be geologically almost completely inactive at this point, Venus is more similar to Earth in its internal composition and in the presence of radioactive elements that can generate heat and maintain active volcanism on the planet.
Furthermore, the Venusian surface appears geologically recent (renewed between hundreds and tens of millions of years ago), with few impact craters, which is more Earth-like than Mars-like.
But Venus does not have a system of tectonic plates like Earth’s, which here dictates how and where volcanoes arise and remain active. This should produce marked differences in the level of volcanic activity on the two planets.
Planetary scientists have already conceived many possible models of the geological dynamics of Venus, ranging from an intensity well below that of Earth to an intensity much higher – but only direct observations of the level of activity will be able to discriminate between these different models.
The finding of the US duo is a first step, but with a single occurrence it is still difficult to make an estimate. Researchers are already comfortable saying that Venus is less active than Io, Jupiter’s volcano-speckled moon. But then even the Earth falls behind.
“Our results make it unlikely that volcanism on Venus has dropped to a small fraction of that on Earth in the last few hundred million years, but there is a wide range of possible activity scenarios that are consistent with Hawaiian-like levels of volcanism on Atla. Regal.”
Depending on the level of activity, it is possible that the recent detection of phosphine in the atmosphere of Venus (in itself controversial) is explainable by purely geological mechanisms, eliminating any action of microorganisms in the Venusian clouds.
All this will be a full plate for the next two missions planned by NASA to Venus. Called DaVinci+ and Veritas, they are scheduled for launches in 2029 and 2031, and will aim to analyze the atmosphere and perform high-resolution mapping of the planet. They will be the first American spacecraft to focus on studying Venus since the end of the Magellan mission.