It is alleged that phosphine on Venus is more likely to be ordinary sulfur dioxide, new study shows

In September, a team led by astronomers in the UK announced that they had detected the chemical phosphine in the clouds of Venus. The report’s discovery, based on observations by two radio telescopes on Earth, surprised many Venus experts. The Earth’s atmosphere contains small amounts of phosphine that can be produced by life. Phosphine on Venus has buzzes that could somehow house the planet, often referred to briefly as a ‘hellscape’, in life in its acid clouds.

Since the initial claim, other science teams have questioned the reliability of phosphine detection. Now a team led by researchers at the University of Washington has used a robust model of the conditions in the atmosphere of Venus to revisit and fully reinterpret the radio telescope observations underlying the initial phosphine claim. As they report in a paper accepted to The Astrophysical Journal and posted on the preprint website arXiv on January 25, the British group probably did not detect phosphine.

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

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

The team led by UW shows that sulfur dioxide, at levels credible to Venus, can not only explain the observations, but also more in line with what astronomers know about the planet’s atmosphere and its chemical environment, which includes sulfuric acid clouds. . In addition, the researchers show that the initial signal did not originate in the cloud layer of the planet, but far above it, in an upper layer of Venus’ atmosphere where phosphine molecules would be destroyed within seconds. This supports the hypothesis that sulfur dioxide produces the signal.

Both the putative phosphine signal and this new interpretation of the data center on radio astronomy. Each chemical compound absorbs unique wavelengths of the electromagnetic spectrum, which include radio waves, X-rays and visible light. Astronomers use radio waves, light and other emissions from planets to learn about their chemical composition, among other things.

In 2017, using the James Clerk Maxwell Telescope, or JCMT, the British leader discovered a function in the radio emission of Venus at 266.94 gigahertz. Both phosphine and sulfur dioxide absorb radio waves near the frequency. To distinguish between the two, the same team obtained follow-up observations from Venus in 2019 using the Atacama Large Millimeter / submillimeter Array, or ALMA. Their analysis of ALMA observations at frequencies where only sulfur dioxide is taken up led the team to conclude that the sulfur dioxide levels in Venus were too low to offset the signal at 266.94 gigahertz, and that it was rather phosphine had to come.

In this new study by the UW-led group, the researchers began modeling conditions within Venus’ atmosphere and used them as a basis to fully understand the features seen – and not seen – in the JCMT and ALMA datasets. to interpret.

“This is what is known as a radiation transfer model, and it contains data from observations of Venus from several decades from various sources, including observatories here on Earth and spacecraft missions such as Venus Express,” said lead author Andrew Lincowski, a researcher at the YOUR Department of Astronomy.

The team used the model to simulate signals of phosphine and sulfur dioxide for different levels of Venus’ atmosphere, and how the signals would be picked up by the JCMT and ALMA in their 2017 and 2019 configurations. Based on the shape of the 266.94-gigahertz signal picked up by the JCMT, the absorption does not come from Venus’ cloud cover, the team reports. Instead, most of the observed signal originated about 50 or more kilometers above the surface in Venus’ mesosphere. At that height, harsh chemicals and ultraviolet radiation will shatter phosphine molecules within seconds.

“Phosphine in the mesosphere is even more brittle than phosphine in Venus’ clouds,” Meadows said. “If the JCMT signal is derived from phosphine in the mesosphere, then the phosphine must be delivered about 100 times as fast as the oxygen in the mesosphere to offset the strength of the signal and the compound’s second lifetime at that height by. the photosynthesis pumped into the earth’s atmosphere. ‘

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

“The antenna configuration of ALMA at the time of the 2019 observations has an undesirable side effect: the signals of gases that occur almost everywhere in Venus’ atmosphere – such as sulfur dioxide – emit weaker signals than gases that are distributed on a smaller scale , “said co-author Alex Akins, a researcher at the Jet Propulsion Laboratory.

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

“They were derived from a low detection of sulfur dioxide due to the artificially weak signal from ALMA,” Lincowski said. “But our modeling suggests that the ALMA data diluted by the line would still be consistent with typical or even large amounts of Venus sulfur dioxide, which could fully explain the observed JCMT signal.”

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

With science teams around the world following up on new observations from Earth’s cloud-covered neighbor, this new study provides an alternative explanation for the claim that something geologically, chemically or biologically must be producing phosphine in the clouds. But while this signal seems to have a more straightforward explanation – with a toxic atmosphere, bone pressure and the hottest temperatures outside the sun of our solar system – Venus remains a world of mysteries, with much left to do explore.