Phosphine discovery hints at life on Venus


Thursday, 17 September, 2020



Phosphine discovery hints at life on Venus

Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes — floating free of the scorching surface, with access to water and sunlight, but needing to tolerate very high acidity. Now an international research team has announced the discovery of a rare molecule known as phosphine — which consists of hydrogen and phosphorus — in those very clouds.

On Earth, this gas is only made industrially or by microbes that thrive in oxygen-free environments. The detection of phosphine, described in the journal Nature Astronomy, could thus point to such extraterrestrial ‘aerial’ life.

The first detection of phosphine in the clouds of Venus was made using the James Clerk Maxwell Telescope (JCMT) in Hawaii — the largest single-dish astronomical telescope in the world designed specifically to operate in the submillimetre wavelength region of the electromagnetic spectrum. According to study leader Professor Jane Greaves of Cardiff University, “When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”

Prof Greaves and her team were then awarded time to follow up their discovery with 45 telescopes of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Both facilities observed Venus at a wavelength of about 1 mm, which is much longer than the human eye can see — only telescopes at high altitude can detect it effectively.

“In the end, 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,” Prof Greaves said.

Artistic impression of Venus depicting a representation of phosphine molecule shown in the inset. Image credit: ESO/M. Kornmesser/L. Calçada & NASA/JPL/Caltech.

Team member and Massachusetts Institute of Technology (MIT) researcher Dr Clara Sousa Silva had previously thought about searching for phosphine as a ‘biosignature’ gas of non-oxygen-using life on planets around other stars, because normal chemistry makes so little of it. The astronomers did, however, run calculations to see if the phosphine could come from natural processes on Venus, as led by MIT’s Dr William Bains.

Some of the team’s ideas included sunlight, minerals blown upwards from the surface, volcanoes and lightning, but none of these could make anywhere near enough of it. Natural sources were found to make at most one-ten-thousandth of the amount of phosphine that the telescopes saw. In contrast, the team found that in order to create the observed quantity of phosphine on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity. That said, any microbes on Venus would likely be very different to their Earth cousins; Earth bacteria can absorb phosphate minerals, add hydrogen and ultimately expel phosphine gas.

The team believes their discovery is significant because they can rule out many alternative ways to make phosphine, but they acknowledge that confirming the presence of ‘life’ needs a lot more work. Although the high clouds of Venus have temperatures up to a pleasant 30°C, they are incredibly acidic — around 90% sulfuric acid — posing major issues for microbes to survive there. MIT researchers are now investigating how microbes could shield themselves inside scarce water droplets.

“The discovery raises many questions, such as how any organisms could survive,” Dr Sousa Silva said. “On Earth, some microbes can cope with up to about 5% of acid in their environment — but the clouds of Venus are almost entirely made of acid.”

The team are now eagerly awaiting more telescope time to establish whether the phosphine is in a relatively temperate part of the clouds, and to look for other gases associated with life. The study results also have implications for the search for life outside the solar system.

“An observed biochemical process occurring on anything other than Earth has the greatest and most profound implications for our understanding of life on Earth, and life as a concept,” said former astronomy student E’Lisa Lee, who took some of the data during her time working as a part-time JCMT telescope operator.

The JCMT instrument that captured this phosphine discovery has since been retired and replaced by a new and more sensitive instrument known as Nāmakanui, named after the big-eyed fish found in the ocean’s dark waters. JCMT’s Deputy Director, Dr Jessica Dempsey, concluded, “Like its namesake … we will turn the far more sensitive Nāmakanui back to Venus in this hunt for life in our universe.”

Top image credit: ©stock.adobe.com/au/WithanTor

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