Sept. 14 (UPI) -- Venus is one of the most inhospitable places in the solar system, but astronomers have long speculated that microbes might be able to survive in the planet's upper atmosphere, according to a study published Monday in the journal Nature Astronomy.
Now, scientists have confirmed the presence of phosphine molecules, featuring hydrogen and phosphorus, inside Venusian clouds -- a possible signature of airborne, extra-terrestrial life.
Astronomers initially discovered the molecule using Hawaii's James Clerk Maxwell Telescope. After the discovery, researchers used the Atacama Large Millimeter/submillimeter Array, in Chile, to gather additional observations.
Both observatories field images in the electromagnetic spectrum, measuring light with wavelengths longer than those of infrared waves or x-rays but shorter than the wavelengths of radio waves or microwaves.
"This was an experiment made out of pure curiosity, really -- taking advantage of JCMT's powerful technology, and thinking about future instruments," lead researcher Jane Greaves said in a news release.
"I thought we'd just be able to rule out extreme scenarios, like the clouds being stuffed full of organisms," said Greaves, a professor of astronomy at Cardiff University in Wales. When we got the first hints of phosphine in Venus' spectrum, it was a shock!"
Greaves first discovered the phosphine signature while working as a visiting research professor at the University of Cambridge's Institute of Astronomy.
Observations using ALMA failed to reveal the phosphine signature in great detail, but the observatory's images did confirm the molecule's presence in Venusian clouds.
"We found that both observatories had seen the same thing -- faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below," said Greaves.
On Earth, phosphine is produced by industrial processes, as well as by microbes that thrive in oxygen-poor environs.
Models designed to simulate Venus' atmosphere helped scientists interpret the data collected by ALMA and JCMT. Their analysis suggests the gas is relatively scarce, comprising just twenty molecules in every billion.
Researchers ran models to see if natural causes -- including sunlight, minerals drafted upwards from the surface, volcanoes or lightning -- might explain the presence of the rare molecule in Venus' upper atmosphere. The simulations showed natural causes can explain, at most, just one ten-thousandth of the amount of phosphine found by ALMA and JCMT.
If microbes are indeed responsible for the production of the phosphine found in Venusian clouds, they likely look much different than the microbes that make phosphine on Earth.
"Phosphine is very hard to make in the oxygen-rich, hydrogen-poor clouds of Venus and fairly easy to destroy," said study co-author Paul Rimmer, researcher at Cambridge's Cavendish Laboratory. "The presence of life is the only known explanation for the amount of phosphine inferred by observations."
"Both of these facts lie at the edge of our knowledge: the observations could be caused by an unknown molecule, or could be caused by chemistry we're not aware of," Rimmer said. "Ultimately, the only way to find out what's really happening is to send a mission into the clouds of Venus to take a sample of the droplets and look at them to see what's inside."
Akatsuki, the Japanese space agency probe that entered orbit around Venus nearly five years ago, is currently mapping a series of dark streaks where ultraviolet light is absorbed. Scientists have suggested that colonies of microbes might explain the unusual streaks.
NASA is also working on plans to send unscrewed spacecraft to Venus.
"Two of the next four candidate missions for NASA's Discovery Program are focused on Venus, as is Europe's EnVision mission, in which NASA is a partner," the space agency said in a news release. "Venus also is a planetary destination we can reach with smaller missions."
Even if Venus' toxic clouds are slightly more forgiving than its scorching-hot surface, they're not exactly inviting -- because they're quite acidic.
"On Earth, some microbes can cope with up to about 5 percent acid in their environment -- but the clouds of Venus are almost entirely made of acid," said co-author Clara Sousa Silva from MIT.
Scientists are currently conducting follow-up experiments to better understand how microbes might be able to shield themselves from the acidic environs inside protective cloud droplets.