Alleged phosphine on Venus is more likely to be regular sulfur dioxide, new study finds

In September, a team led by astronomers in the UK announced that it had detected the chemical phosphine in the thick clouds of Venus. The detection the team reported, based on observations from two terrestrial radio telescopes, surprised many Venus experts. The Earth’s atmosphere contains small amounts of phosphine, which can be produced by life. The phosphine on Venus generated a buzz that the planet, often succinctly presented as a “landscape of hell”, could somehow shelter life in its acid clouds.

Since this initial assertion, other scientific teams have questioned the reliability of the detection of phosphine. Now, a team led by researchers at the University of Washington has used a robust model of conditions in the atmosphere of Venus to fully review and reinterpret the radio telescope observations underlying the original phosphine claim. As they report in an accepted document of The astrophysical journal and posted Jan. 25 to the arXiv pre-print site, the UK-led group was probably not detecting phosphine at all.

“Instead of phosphine in the clouds of Venus, the data is consistent with an alternative hypothesis: they detected sulfur dioxide,” said co-author Victoria Meadows, professor of astronomy at UW. “Sulfur dioxide is the third most common chemical compound in the atmosphere of Venus, and it is not considered a sign of life.”

The team behind the new study also includes scientists from NASA’s Caltech-based Jet Propulsion Laboratory, NASA Goddard Space Flight Center, Georgia Institute of Technology, NASA Ames Research Center and the University. from California to Riverside.

The UW-led team shows that sulfur dioxide, at plausible levels for Venus, can not only explain the observations, but is also more consistent with what astronomers know about the planet’s atmosphere and its chemical environment. punitive, which includes clouds of sulfuric acid. In addition, the researchers show that the initial signal did not come from the cloud layer of the planet, but well above, in an upper layer of the atmosphere of Venus where the phosphine molecules would be destroyed in seconds. This further supports the hypothesis that sulfur dioxide produced the signal.

The alleged phosphine signal and this new interpretation of the Radio Astronomy Data Center. Each chemical compound absorbs unique wavelengths of the electromagnetic spectrum, which includes radio waves, x-rays, and visible light. Astronomers use radio waves, light, and other emissions from the planets to learn about their chemical makeup, among other properties.

In 2017, using the James Clerk Maxwell Telescope, or JCMT, the UK-led team discovered a characteristic in Venus’ radio broadcasts at 266.94 gigahertz. Phosphine and sulfur dioxide absorb radio waves near this frequency. To differentiate the two, in 2019 the same team obtained tracking observations of Venus using the Atacama Large Millimeter / submillimeter Array, or ALMA. Their analysis of ALMA observations at frequencies where only sulfur dioxide absorbs led the team to conclude that the sulfur dioxide levels in Venus were too low to account for the signal at 266.94 gigahertz, and that rather, it must have come from phosphine.

In this new study led by the group led by UW, the researchers began by modeling the conditions in the atmosphere of Venus, and using them as the basis for comprehensively interpreting the features that were seen – and not seen – in them. JCMT and ALMA datasets.

“It’s called a radiative transfer model, and it integrates data from decades of Venus observations from a number of sources, including observatories here on Earth and space missions like Venus Express.” said lead author Andrew Lincowski, a researcher with the Department of Astronomy at UW.

The team used this model to simulate the phosphine and sulfur dioxide signals for different levels of the atmosphere of Venus, and how these signals would be picked up by the JCMT and ALMA in their 2017 and 2019 setups. Based on the shape of the 266.94 gigahertz signal picked up by the JCMT, absorption was not coming from the cloud layer of Venus, the team reports. Instead, most of the observed signal came from about 50 miles or more above the surface, in the mesosphere of Venus. At this altitude, harsh chemicals and ultraviolet radiation would tear apart the phosphine molecules in seconds.

“The phosphine in the mesosphere is even more fragile than the phosphine in the clouds of Venus,” Meadows said. “If the JCMT signal was from phosphine in the mesosphere, then to account for the signal strength and the sub-second lifetime of the compound at that altitude, the phosphine would have to be delivered to the mesosphere about 100 times. the oxygen level. pumped into the earth’s atmosphere by photosynthesis. “

The researchers also found that the ALMA data likely significantly underestimated the amount of sulfur dioxide in Venus’ atmosphere, an observation the UK-led team used to claim that most of the signal from 266.94 gigahertz was from phosphine.

“The configuration of ALMA’s antenna at the time of the 2019 observations has an unwanted side effect: Signals from gases found almost anywhere in Venus’ atmosphere – like sulfur dioxide – emit signals weaker than gases distributed on a smaller scale, ”said co-author Alex Akins, researcher at the Jet Propulsion Laboratory.

This phenomenon, known as spectral line dilution, would not have affected the JCMT observations, leading to an underestimation of the amount of sulfur dioxide observed by the JCMT.

“They inferred a weak detection of sulfur dioxide due to this artificially weak signal from ALMA,” Lincowski said. “But our modeling suggests that the diluted online ALMA data would still have been consistent with typical or even significant amounts of sulfur dioxide from Venus, which could fully explain the observed JCMT signal.”

“When this new discovery was announced, the reported low sulfur dioxide abundance was at odds with what we already know about Venus and its clouds,” Meadows said. “Our new work provides a comprehensive framework that shows how typical amounts of sulfur dioxide in the mesosphere of Venus can explain both signal detections, and non-detections, in JCMT and ALMA data, without the need for phosphine. “

With scientific teams around the world following new observations of Earth’s cloud-shrouded neighbor, this new study provides an alternative explanation for the claim that something geologically, chemically, or biologically must generate phosphine in them. clouds. But while this signal appears to have a simpler explanation – with a poisonous atmosphere, overwhelming pressure, and some of the hottest temperatures in our solar system outside of the sun – Venus remains a world of mysteries, with a lot to explore.