Scientists have long considered Venus, which has a thick, acidic atmosphere, unfit for life.Credit: Datlav van Ravensway / Science Photo Library
Signs of gas phosphine in Venus’s atmosphere have diminished slightly – but according to new data analysis, they are still there.
In September, they made headlines when an international team of astronomers reported finding a possible marker of life – phosphine – in the planet’s atmosphere... Some studies quickly followed, questioning their observations and findings. Now the same team has re-analyzed some of its data, citing a processing error in the original data used. The researchers confirmed the phosphine signal, but say it is more obscure than before.
The work is an important step in resolving the most exciting Venus debate in decades. “I’ve been waiting my whole life for this,” says Sanjay Limaye, a planetary scientist at the University of Wisconsin in Madison.
A re-analysis based on radio telescope observations in the Attackma Large Millimeter / Submillimeter Array (ALMA) in Chile, concludes that the average phosphin level in Venus is about 1 part per billion – about one-seventh of the previous estimate. Contrary to their original report, scientists now describe their discovery of phosphine on Venus as “temporary”.2.
This is the team’s first public response to the criticism leveled against him in the last two months. “The scientific process is working,” says Bob Grimm, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who is not involved in any phosphine studies. Researchers pursue large claims with great effort to gather evidence and prove or disprove them.
Another look
In its September report, the team used data from the ALMA and the James Clark Maxwell Telescope (JCMT) in Hawaii to find it. Jane Greaves, team leader and astronomer at Cardiff University in the UK, said she and her colleagues worked again because they knew there was a strong signal in the original ALMA data that could affect the results. Alma posted the revised data on November 16, and Greaves’ team ran a new analysis and sent it to the printprint server archive.rg before conducting a peer review that night. Posted on “We’re acting like crazy,” he told a meeting of NASA’s community forum, Venus Exploration Analysis Group, on November 17.
According to Greaves and his colleagues, the ALMA data show a spectrum signature of phosphine, a molecule composed of one phosphorus and three hydrogen atoms. They say no other compound will be able to explain the data. Be careful to find phosphine on Venus as microorganisms produce gas on Earth. If the signal is real and indeed due to phosphine, it is possible that microbes living and flowing between the clouds of the planet could produce gas.4,3 – But it is also possible that there may be inanimate sources for phosphine that scientists have yet to identify. To determine whether any of these scenarios are true, researchers first need to confirm the presence of phosphine.
In a review of the original study, the researchers suggested that the signal referred to as phosphine may actually come from sulfur dioxide, a gas that is common in Venus clouds but is not produced by life there.5. Greaves and his team responded in their recent report that this may not be the case, based on how the phosphine fingerprint appears in the data collected by another telescope they used, JCMT. Other critics have focused on the difficulty of signaling phosphine signals from complex data.
The re-analysis showed the concentration of phosphine in the atmosphere of Venus which is often in the billions. This means that gas levels in different places on Earth can rise and fall over time, Greaves said – a condition similar to the methane spikes seen on Mars.
Another new amount of evidence supports phosphine on Venus. Inspired by Greaves’ report, a team led by Rakesh Mogul, a biochemist at California State Polytechnic University in Pomona, California, recently dug up decades-old data from NASA’s 1978 Pioneer-Venus mission. The spacecraft dropped a probe from Earth’s atmosphere that measured the chemistry of the clouds as they fell. Find a phosphorus compound that can be a phosphin or other phosphorus based molecule6. “We believe that the easiest gas to match the data is phosphine,” Mogul said at a meeting on November 17.
Still working ahead
Where phosphine comes from remains a mystery. Even at a fraction-billion level, it was greatly explained by volcanic eruptions on the planet’s surface or by lightning strikes in the atmosphere, several scientists said at the meeting. But phosphorus-based compounds can be produced by geological processes and then converted into other chemicals, such as phosphine, which grows in clouds, Mogul said.
Japan’s Akatsuki, the only spacecraft currently orbiting Venus, will not be able to carry an instrument that could help settle the debate. The Indian Space Research Organization is planning a Venus mission that will begin in 2025 and could potentially take devices capable of exploring phosphine. Meanwhile, Greaves and other researchers are applying for more time on Earth-based telescopes, including ALMA.
David Greenspan, an astrobiologist at the Washington DC-based Planetary Science Institute, says researchers are investigating many other aspects of Venus other than phosphine. “There are 1,001 reasons to go back to Venus, and if phosphine is ‘removed’ by further observations and analysis, there are still 1,000 reasons left.”
