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By The Washington Post 
9h ago
Marisa Iati and Joel Achenbach
An international team of astronomers has detected a rare molecule in Venus’s atmosphere that could be produced by living organisms, according to a study published Monday.
The discovery instantly brings the brightest planet in the night sky back into the conversation about where to look for extraterrestrial life.
The researchers made it clear that this is not a direct detection of life on Venus.
But astronomical observations confirmed the highly intriguing presence of the chemical phosphine near the top of the acidic clouds that cover the planet.
Phosphine is a simple molecule produced on Earth by bacteria and through industrial processes. As a result, it is on the list of molecules (oxygen is another) that scientists consider possible “biosignatures” of life on planets the size of Earth, whose atmospheres can be seen through telescopes.
The researchers said they do not know of a non-biological explanation for the relatively high abundance of the molecule in Venus’ atmosphere.
“We did everything we could to show what else could cause phosphine in the abundance we found on Venus. And we didn’t find anything. We didn’t find anything close,” said Clara Sousa-Silva, molecular astrophysicist at the Massachusetts Institute of Technology and co-author of the published paper. Monday in the journal Nature Astronomy.
Venus burns on the surface, but there are layers of the atmosphere where temperatures and pressures are moderate and where solar radiation is not too intense. For decades, some planetary scientists have speculated that microbes could be circulating in the atmosphere, which is dominated by sulfuric acid and carbon dioxide and has only tiny traces of water vapor.
Venus has long been eclipsed by Mars as a possible abode of life, because the planet’s dense atmosphere and proximity to the sun have led to a runaway greenhouse effect, leading to hellish surface temperatures and crushing atmospheric pressures. Robotic probes have revealed a landscape that appears inhospitable to any imaginable form of life.
Mars has always seemed more compatible with life and potential human exploration, and has been the target of multiple robotic missions, including the most recent one from NASA’s Mars 2020 rover, Perseverance. NASA is considering proposals for two relatively low-cost robotic missions to Venus, but they have not been approved. Monday’s announcement could prompt NASA and other space agencies to take a closer look at Venus.
“For something this big, we need follow-up confirmations, we need to have a strong scientific debate,” said Casey Dreier, senior adviser for space policy at the Planetary Society, a pro-space nonprofit organization that was not involved in the new research. “Ultimately, we are going to need missions to Venus, and maybe even bring samples back to Earth.”
Sarah Stewart Johnson, a planetary scientist at Georgetown University who was also not involved in the new study, echoed that sentiment in an email: “This is exactly the kind of anomalous finding we should follow. There may be things missing. Photochemically, which we just don’t understand, but it is possible that phosphine is the result of a biotic process, and its detection surely increases the chances of life. “
Sousa-Silva said he had spent years studying phosphine as a possible biological signature in the atmospheres of exoplanets, the planets that orbit distant stars. But she hadn’t considered looking for phosphine within our own solar system.
Then, just over a year ago, she received an email from Cardiff University astronomer Jane Greaves and lead author of the new paper, who said her telescopic observations within the solar system had revealed signs of phosphine on Venus.
Follow-up observations with another telescope confirmed that initial detection.
Phosphine is a toxic, smelly gas that is extremely poisonous and has been used in chemical weapons. The molecule is made up of one phosphorus atom and three hydrogen atoms, and is shaped like a pyramid with phosphorus on top. These atoms do not favor each other, and therefore the molecule is generally rare in nature. To create a phosphine molecule, Sousa-Silva said, an unusual force or mechanism is required.
Living things can create the molecule through a metabolic pathway that is not fully understood, he said. And the extreme forces of nature can produce the molecule. For example, phosphine has been detected in the atmospheres of Jupiter and Saturn, the two gas giants of the solar system, where gravity creates extreme environments.
But Venus, like Earth, is a relatively small rocky planet. The researchers considered many possible mechanisms for the creation of phosphine, including volcanoes and meteorite impacts, but couldn’t get the numbers correct.
“On Venus, we don’t know of any mechanism that can produce phosphine spontaneously, because it is very difficult to produce,” Sousa-Silva said.
The scientists involved in this new detection were careful not to exaggerate their findings. For example, while there is no known non-biological source of phosphine on Venus, that doesn’t mean there isn’t, Sousa-Silva said.
Any claim of detection of life beyond Earth carries a heavy burden of proof. The search for alien life has had a long history of exciting hypotheses, spiteful debates, and crushing disappointments. To date, no extraterrestrial life has been found anywhere.
Mars has periodically generated a great deal of excitement, only for the claims to erode in the harsh light of further research. In several high-profile cases, something that seemed irrefutably biological resulted in closer examination to be potentially explainable through more prosaic processes.
“My first reaction, as always, is skepticism,” said Bruce Jakosky, a planetary scientist at the University of Colorado, when asked about the new report. “One of the things I’ve seen is that when people discover cool new things, their first thought is life, and then they can come up with plausible alternative explanations for what they saw.”
Still, he said, the phosphine discovery is “intriguing.”
A similar situation has arisen on Mars, where methane has been detected in the atmosphere. That prompted speculation that it was produced by Martian organisms. But this remains unsolved, because there are non-biological explanations for the gas’s presence, according to NASA. An international mission specifically designed to search for it, the ExoMars Trace Gas Orbiter, couldn’t find it at all.
Monday’s announcement suggests that perhaps scientists should spend more time looking elsewhere, at the second rock from the Sun.
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