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The search for life beyond Earth has largely revolved around our rocky red neighbor. NASA has launched several rovers over the years, with a new one currently en route, to examine the dusty surface of Mars for signs of water and other indications of habitability.
Now, in a surprising twist, scientists at MIT, Cardiff University and elsewhere have observed what may be signs of life in the clouds of our other, even closer planetary neighbor, Venus. While they have found no direct evidence of living organisms there, if their observation is truly associated with life, it must be some kind of “aerial” life form in the clouds of Venus, the only habitable portion of what is otherwise. a scorched and inhospitable terrain. world. Their discovery and analysis is published today in the journal Nature astronomy.
The astronomers, led by Jane Greaves of Cardiff University, detected a spectral fingerprint, or light-based signature, of phosphine in Venus’s atmosphere.. MIT scientists have previously shown that if this stinky, poisonous gas were ever detected on a rocky terrestrial planet, it could only be produced by a living organism there. The researchers conducted the detection using the James Clerk Maxwell Telescope (JCMT) in Hawaii and the Atacama Large Millimeter Array (ALMA) observatory in Chile.
The MIT team followed up the new observation with a comprehensive analysis to see if something other than life could have produced phosphine in the harsh sulfuric environment of Venus. Based on the many scenarios they considered, the team concludes that there is no explanation for the phosphine detected in the clouds of Venus, other than the presence of life.
“It’s very difficult to prove something negative,” says Clara Sousa-Silva, a research scientist in the Department of Earth, Atmospheric and Planetary Sciences (EAPS) at MIT. “Now, astronomers will think of all the ways to justify lifeless phosphine, and I like that. Please do so, because we are at the end of our ability to show abiotic processes that can produce phosphine. “
“This means this is life or some kind of physical or chemical process that we don’t expect to occur on rocky planets,” adds EAPS co-author and research scientist Janusz Petkowski.
Other MIT co-authors include William Bains, Sukrit Ranjan, Zhuchang Zhan, and Sara Seager, who is a Class of 1941 Professor of Planetary Sciences with appointments to the Departments of Physics and Aeronautics and Astronautics, along with collaborators from the University of Cardiff. the University of Manchester, the University of Cambridge, the MRC Molecular Biology Laboratory, Kyoto Sangyo University, Imperial College, the Royal Greenwich Observatory, the Open University and the East Asian Observatory.
A search for exotic things
Venus is often referred to as Earth’s twin, as neighboring planets are similar in size, mass, and rock composition. They also have significant atmospheres, although that’s where their similarities end. Where Earth is a habitable world of temperate oceans and lakes, the surface of Venus is a seething landscape, with temperatures reaching 900 degrees Fahrenheit and suffocating air that is drier than the driest places on Earth.
Much of the planet’s atmosphere is also quite inhospitable, permeated with thick clouds of sulfuric acid and cloud droplets that are billions of times more acidic than the most acidic environment on Earth. The atmosphere also lacks nutrients that exist in abundance on the surface of a planet.
“Venus is a very challenging environment for life of any kind,” says Seager.
However, there is a narrow, warm band within Venus’s atmosphere, 30 to 60 kilometers above the surface, where temperatures range from 30 to 200 degrees Fahrenheit. Scientists have speculated, with much controversy, that if life exists on Venus, this layer of the atmosphere, or cloud cover, is probably the only place where it would survive. And it just so happens that this cloud layer is where the team observed phosphine signals.
“This phosphine signal is perfectly positioned where others have conjectured that the area could be habitable,” says Petkowski.
The detection was first made by Greaves and his team, who used the JCMT to focus on Venus’s atmosphere in search of light patterns that could indicate the presence of unexpected molecules and possible signatures of life. When she detected a pattern indicating the presence of phosphine, she contacted Sousa-Silva, who has spent most of her career characterizing the toxic and stinky molecule.
Sousa-Silva initially assumed that astronomers could search for phosphine as a biological signature on much more distant planets. “I was thinking really far away, many parsecs away, and I wasn’t really thinking literally about the planet closest to us.”
The team followed up the initial observation of Greaves using the more sensitive ALMA observatory, with the help of Anita Richards of the ALMA Regional Center at the University of Manchester. Those observations confirmed that what Greaves observed was in fact a pattern of light that matched the phosphine gas it would emit inside the clouds of Venus.
The researchers then used a model of the Venusian atmosphere, developed by Hideo Sagawa of Kyoto Sangyo University, to interpret the data. They discovered that phosphine on Venus is a minor gas, existing in a concentration of about 20 out of every billion molecules in the atmosphere. Although that concentration is low, the researchers note that the phosphine produced by life on Earth can be found in even lower concentrations in the atmosphere.
The MIT team, led by Bains and Petkowski, used computer modeling to explore all possible chemical and physical pathways not associated with life that could produce phosphine in the harsh environment of Venus. Bains considered several scenarios that could produce phosphine, such as sunlight, surface minerals, volcanic activity, a meteorite, and lightning. Ranjan, together with Paul Rimmer of the University of Cambridge, modeled how phosphine produced through these mechanisms could accumulate in Venusian clouds. In all the scenarios they considered, the phosphine produced would only equal a small fraction of what the new observations suggest is present in clouds on Venus.
“We really went through every possible pathway that could produce phosphine on a rocky planet,” says Petkowski. “If this is not life, then our understanding of rocky planets is very poor.”
A life in the clouds
If there is indeed life in the clouds of Venus, the researchers believe it is an aerial form, existing only in the temperate cloud cover of Venus, well above the boiling volcanic surface.
“A long time ago, Venus was thought to have oceans and was probably habitable like Earth,” says Sousa-Silva. “As Venus became less hospitable, life would have had to adapt, and now they could be in this tight envelope of the atmosphere where they can still survive. This could show that even a planet at the edge of the habitable zone could have an atmosphere with a local habitable air envelope. “
In a separate line of research, Seager and Petkowski have explored the possibility that the lower layers of Venus’s atmosphere, just below the cloud cover, could be crucial to the survival of a hypothetical Venusian biosphere.
“In principle, it can have a life cycle that sustains life in the clouds in perpetuity,” says Petkowski, who envisions that any Venusian aerial life is fundamentally different from life on Earth. “The liquid medium on Venus is not water, as it is on Earth.”
Sousa-Silva is now leading an effort with Jason Dittman at MIT to further confirm phosphine detection with other telescopes. They also hope to map the presence of the molecule in the atmosphere of Venus, to see if there are daily or seasonal variations in the signal that suggest activity associated with life.
“Technically, biomolecules have been found in the atmosphere of Venus before, but these molecules are also associated with thousands of things other than life,” says Sousa-Silva. “The reason phosphine is special is that without life it is very difficult to produce phosphine on rocky planets. Earth has been the only terrestrial planet where we have found phosphine, because there is life here. Until now.”
This research was supported, in part, by the Science and Technology Facilities Council, the European Southern Observatory, the Japan Society for the Promotion of Science, the Heising-Simons Foundation, the Change Happens Foundation, the Simons Foundation and Horizon de the European Union. Research and innovation program 2020.
