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For almost a year, scientists have been locked in a debate over whether or not Venus has signs of life hidden in its clouds – the theory is based on traces of phosphine gas in its upper atmosphere, a sign of biological activity.
Jonathan Lunine, chairman of the Department of Astronomy at Cornell University, and his graduate student Ngoc Truong are among those who are not convinced of the habitability of this scorching planet. Instead, they suggest that phosphine from Venus may have reached the planet’s upper atmosphere through volcanic eruptions. And in a new newspaper, they want to sort things out once and for all.
“That’s really why we went ahead and pursued this,” Lunine said. Reverse.
“We have estimated that this is the most plausible source of phosphine, it is volcanism and not biology.
In the study, published Monday in the Proceedings of the National Academy of Sciences, the team suggests that rather than being habitable, Venus is actually a geologically active world. Specifically, they find evidence of volcanism occurring today or in the recent past of the planet – this would explain phosphine gas.
While the latest twist in the phosphine debate puts a slight damper on the case for life on Venus, it will help scientists in their search for other Earth-like planets – which may harbor life – orbiting around different stars.
WHAT’S UP – Following a landmark discovery made last year that scientists said was clear evidence that Venus could harbor life because it had phosphine in its clouds, Lunine and her team began exploring a alternative explanation for developer gas.
Using observations from the James Clerk Maxwell Ground Telescope in Hawaii and the Atacama Large Millimeter Array (ALMA) in northern Chile, Lunine and her team created a model of Venus, in which the planet was active. volcanic.
The model suggests that some phosphorus-containing compounds could be lurking in Venus’ mantle, which lies beneath the planet’s surface. These compounds – called phosphites – could apparently find their way to the surface and then be ejected by explosive volcanism into the stratosphere of Venus.
This is a layer of the planet’s upper atmosphere where phosphites would react with other chemicals in the atmosphere, such as sulfuric acid and water. If this happened, the phosphites would be converted to phosphine.
“The initial hypothesis was that the phosphine discovered indicated life,” says Lunine. “We don’t think so, we think of points of volcanism.”
HERE IS THE CONTEXT – In September 2020, a team of scientists claimed to have detected traces of phosphine gas in the atmosphere of Venus.
Phosphine is considered a biosignature gas on Earth, which means that it is usually produced by a living organism. When looking for signs of life on other planets, scientists typically look for traces of a “bio-signature” gas to help them identify if a planet could possibly harbor life – phosphine is on the list.
The first results were met with as much enthusiasm as skepticism, as some scientists doubt that Venus can harbor life now or ever. It has to do with Venus itself.
The surface of Venus displays temperatures of up to 900 degrees Fahrenheit due to a dense atmosphere of carbon dioxide that retains heat. At the same time, the scorching world is spinning slowly and in the opposite direction of most planets, but its winds blow as fast as hurricanes, sending the acid clouds of Venus circling the planet once every five days.
Basically, on the list of habitable worlds, Venus rarely makes the cut.
Dig into the details – Since the September 2020 article, other scientists have suggested alternative reasons for the presence of phosphine on Venus, including that it is not phosphine at all, but possibly sulfur dioxide.
But the new study bases its alternative theory on both new findings and past evidence that Venus harbors volcanic activity.
“There has been a lot of circumstantial evidence over the years,” says Lunine.
In 1978, NASA’s Pioneer Venus orbiter mission discovered variations in sulfur dioxide in the upper atmosphere of Venus. Sulfur dioxide is released from volcanoes, and the amount discovered at the time would put the magnitude of volcanic activity on Venus similar to that of the catastrophic Krakatoa volcanic eruption of 1883 in Indonesia. This eruption was so powerful that it changed the Earth’s climate for several years after it occurred.
Meanwhile, radar images from the Magellan spacecraft in the 1990s showed geological features on Venus that were also indicative of recent volcanic activity.
“Much of the surface of Venus appears to be relatively young,” says Lunine.
“It has a few impact craters, but there appears to have been an episode of large-scale volcanism recently.”
Venus is similar to Earth in many ways, with similar size, density, and composition. It makes sense that Venus gets rid of its heat the same way Earth does, through volcanoes.
WHY IS IT IMPORTANT – While the recent study does not point to further evidence of Venus’ potential habitability, it does give scientists a rare opportunity to study a planet much like Earth but at a different stage in its evolution.
Venus’s atmosphere is made up mostly of carbon dioxide and traps heat in the same way greenhouse gases do here on Earth. This is why Venus is often used as a strange view of the future of Earth.
Scientists believe that Venus may have started out like Earth early in its history with water flowing on its surface. However, as the planet warmed, the oceans evaporated and its surface temperature grew so high that all life would have been destroyed.
“This allows us to study a planet the size of Earth, where the geology is extremely different,” says Lunine. “It also gives us some ground truth to look at Earth-sized planets around other stars.”
AND AFTER – With so much attention on Mars, Venus has been neglected in the search for life off Earth for over 30 years. But everything is about to change soon.
NASA is currently preparing two missions to Venus to study the atmosphere and geological history of the planet.
The VERITAS mission, which stands for Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy, will map the geological features of Venus.
The spacecraft will create 3D topographic maps of the planet’s surface and measure its gravitational pull. The purpose of understanding the geological history of Venus is to find out why the planet, which started out very similar to Earth, developed very differently over time.
Abstract: We hypothesize that trace phosphides formed in the mantle are a plausible abiotic source of Venusian phosphine observed by Greaves et al. [Nat. Astron., https://doi.org/10.1038/ s41550-020-1174-4 (2020)]. In this hypothesis, small quantities of phosphides (P3− bound to metals such as iron), coming from a deep mantle, are brought to the surface by volcanism. They are then ejected into the atmosphere as volcanic dust by explosive volcanic eruptions, which have been cited by others to explain the episodic changes in sulfur dioxide observed in the atmosphere. [Esposito, Science 223, 1072–1074 (1984)]. There they react with sulfuric acid in the aerosol layer to form phosphine (2 P3− + 3H2SO4 = 2PH3 + 3SO4 2-). We dispute the conclusion of Bains et al. [arXiv:2009.06499 (2020)] that the volcanic rates for such a mechanism would be implausibly high. We consider a mantle with a redox state similar to that of Earth, magma from the depths of the mantle – a likely scenario for the origin of plume volcanism on Venus – and episodically high but plausible rates of volcanism on a devoid of Venus. of plate tectonics. We conclude that volcanism could provide a sufficient amount of phosphide to produce phosphine. Our conclusion is supported by remote sensing observations of the Venusian atmosphere and surface which have been interpreted to indicate currently active volcanism.
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