If life doesn’t exist on Mars, then how about on Venus?
Astronomers find chemical phosphine above planet, suggesting microbes exist
High in the toxic atmosphere of the planet Venus, astronomers on Earth have discovered signs of what might be life.
If the discovery is confirmed by additional telescope observations and future space missions, it could turn the gaze of scientists toward one of the brightest objects in the night sky. Venus, named after the Roman goddess of beauty, roasts at temperatures of hundreds of degrees and is cloaked by clouds that contain droplets of corrosive sulfuric acid. Few have focused on the rocky planet as a habitat for something living.
Instead, for decades, scientists have sought signs of life elsewhere, usually peering outward to Mars and more recently at Europa, Enceladus and other icy moons of the giant planets.
The astronomers, who reported the finding Monday in a pair of papers, have not collected specimens of Venusian microbes, nor have they snapped any pictures of them. But with powerful telescopes, they have detected a chemical — phosphine — in the thick Venus atmosphere. After much analysis, the scientists assert that something now alive is the only explanation for the chemical’s source.
Some researchers question this hypothesis, and they suggest instead that the gas could result
from unexplained atmospheric or geologic processes on a planet that remains mysterious.
“This is an astonishing and ‘out of the blue’ finding,” said Sara Seager, a planetary scientist at the Massachusetts Institute of Technology.
“We know that it is an extraordinary discovery,” said Clara Sousa-Silva, a molecular astrophysicist at Harvard University whose research has focused on phosphine and is another of the authors. “We may not know just how extraordinary without going back to Venus.”
Many scientists think that Venus was once covered
in water and possessed an atmosphere where life as we know it could have flourished.
In earlier days of the solar system, Earth was not so hospitable to the likes of us. There was life here then, even an entire biosphere that did not survive in the oxygen-rich environment that later developed. And much as Earth over time became a home for jellyfish, ferns, dinosaurs and Homo sapiens, Venus was transformed by something into a hell.
Today, the second planet from the sun has an atmosphere stifled by carbon dioxide gas and surface temperatures that average more than 800 degrees Fahrenheit. The dense atmosphere of Venus exerts a pressure of more than 1,300 pounds per square inch on anything
at the surface.
Space programs have tried dozens of robotic missions to Venus, many of them in the Soviet Union’s Venera series. But the planet eats metal, within minutes melting down and crushing spacecraft that have landed there.
Although the surface of Venus is like a blast furnace, a cloud layer just 31 miles below the top of its atmosphere may reach temperatures as low as 86 degrees Fahrenheit and has a pressure similar to that at ground level on Earth. Many planetary scientists, including Carl Sagan and Harold Morowitz, who proposed the idea 53 years ago, have hypothesized life may exist there.
Jane Greaves, an astronomer at Cardiff University in Wales, set out in
June 2017 to test that hypothesis using the James Clerk Maxwell Telescope in Hawaii, looking for signs of various molecules on Venus. Different species of molecules will absorb radio waves coming through the clouds at different characteristic wavelengths. One of the chemicals is phosphine. She did not expect to find it.
“I got intrigued by the idea of looking for phosphine, because phosphorus might be a bit of a sort of go-no-go for life,” Greaves said.
Chemists compare phosphine to a pyramid — one atom of phosphorus topping a base of three hydrogen atoms. NASA spacecraft Cassini detected it in the atmospheres of Jupiter and Saturn. In that setting, Sousa-Silva said, life is
not necessary to form phosphine. The immense heat and pressures can jam the phosphorous and hydrogen atoms together to form the molecule.
But on smaller, rocky planets like Earth and Venus, the researchers say, there is not enough energy to produce copious amounts of phosphine in the same way. There is one thing, however, that appears to be very good at producing it: anaerobic life, or microbial organisms that don’t require or use oxygen.
On such worlds, “as far as we can tell, only life can make phosphine,” SousaSilva said.
Here on Earth, phosphine is found in our intestines, in the feces of badgers and penguins, and in some deep sea worms, as well as other biological environments associated with anaerobic organisms. It is also extremely poisonous. Militaries have employed it for chemical warfare, and it is used as a fumigant on farms. On the TV show “Breaking Bad,” the main character, Walter White, makes it to kill two rivals.
Sousa-Silva was surprised when Greaves said that she had detected phosphine.
If there really was phosphine on Venus, she believed there could be no other obvious explanation than anaerobic life.
Volcanic activity and lightning on Venus would not be sufficient to add more of this constantly disappearing phosphine, according to the researchers’ models. But living things could emit enough of the gas.