Did scientists detect chemical signals from Venusian microorganisms?

Four takeaways from astronomer Cullen Blake on what this potentially groundbreaking study shows and what comes next for scientists who are keen to understand these faraway chemical signals.

an artists impression of venus, shown half in shadow with a cream and tan colored atmosphere
An artistic impression of Venus, where scientists recently confirmed the detection of phosphine molecules in the atmosphere. Because phosphine was detected at levels that researchers couldn’t attribute to any inorganic factors, many in the field hypothesize that Venusian microorganisms could be responsible. (Image: ESO/M. Kornmesser & NASA/JPL/Caltech)

Amid a steady stream of news on coronavirus, hurricane season, and raging wildfires, a recent study has many asking a new, extremely unexpected question for 2020: Is there life on Venus? 

A study, published in Nature Astronomy, describes the presence of a gas called phosphine in Venus’ atmosphere at levels that researchers couldn’t attribute to any inorganic factors. Because of these observations, many in the field hypothesize that Venusian microorganisms could be responsible for producing such high levels of phosphine. 

To learn more about what these potentially groundbreaking results mean and what comes next, Penn Today spoke with astronomer Cullen Blake, who points to four key takeaways from the study.  

The possibility of life on Venus was first proposed in the 1960’s. In more recent years, phosphine became one of the key candidates for identifying life on other planets. 

Shortly before the Apollo 11 moon landing, astronomers Carl Sagan and Harold Morowitz proposed that, although the surface of Venus was inhospitable, the planet’s atmosphere could potentially support life thanks to its cooler, Earthlike temperatures and pressures tens of kilometers above the surface. 

In more recent years, astronomers like Sara Seager, a co-author of this latest paper and who recently gave a virtual seminar at Penn, have been collaborating with chemists to find biosignature gases, ones that are produced by living organisms and that accumulate at detectable levels. “They were trying to think of things in Earth’s atmosphere that are not made by natural processes very efficiently. So if you turn off life on Earth, this is what goes away, and phosphine was identified in that effort,” Blake says. 

Phosphine is a noxious, flammable gas that is only made by certain types of anaerobic bacteria, ones that live in oxygen-free environments, so its presence is thought to correspond with that of living organisms. 

A team of chemists and astronomers found a “whoppingly huge” phosphine signal that they can’t attribute to any non-biological sources. 

Data collected by the James Clerk Maxwell Telescope in Hawaii and the Atacama Large Millimeter/submillimeter Array in Chile is “unambiguously phosphine,” with the paper’s results showing a strong signal at the chemical’s specific frequency. “One thing that stood out is that the data is impressive; the level of detection is very strong,” says Blake. “By physics standards, it’s a whoppingly huge signal.”

an image of Venus with two chemical spectra superimposed on top
A real image of Venus, taken with Atacama Large Millimeter Array (ALMA), with two superimposed spectral data collected by ALMA (in white) and the James Clerk Maxwell Telescope (JCMT; in grey). Phosphine absorbs some of the millimeter waves produced at lower altitudes, so astronomers can pick up a phosphine absorption signature as a dip in light from the planet. (Image: ALMA (ESO/NAOJ/NRAO), Greaves et al. & JCMT (East Asian Observatory))

The explanation of bacteria present at high altitudes on Venus seems plausible based on these data, says Blake. To support their hypothesis, the researchers developed a large chemical model that takes into account all of the known conditions on the planet to see if anything else, such as volcanoes or lightning, could explain these levels of phosphine. Their model showed that, even with all other factors taken into account, the amount of phosphine predicted versus what was actually found was off by a huge factor. 

“It’s at some level an outstanding explanation, and it could be that there’s some bit of chemistry they don’t know on Venus, but the numbers seem reasonable,” Blake says, adding that during the press conference, the researchers did emphasize that they were not solely claiming to have detected life on Venus but were simply reporting new chemistry that could be explained by the presence of life.

A combination of additional observations from Earth, as well as ongoing and new inner solar system missions, will be essential for confirming this finding. 

There are a few different things that scientists can do, both now and on longer time scales, to confirm this potentially groundbreaking discovery. “Phosphine has one strong absorption that is used to identify it, so presumably there are other chemical features at other frequencies, so you can go to look and confirm that you see those same chemical fingerprints,” says Blake. Additional ground-based research could also include studying phosphine itself in more detail to find other ways that it could be measured from a distance.  

So far, the discovery has prompted the European Space Agency’s BepiColombo, which is on its way to Mercury, to make a second flyby of Venus. “It’s got some spectrometry instruments that can study the atmosphere in more detail,” Blake says. “It has a complex trajectory, and I’m not sure how close it will have to be to get good data, but it will cross close to Venus a couple of times.”

There’s also the possibility that NASA could put together some short timescale missions, on the order of a decade long project, that could conduct follow-up studies on the planet itself. Because of Venus’ dense atmosphere, it would be possible to deploy blimps or hydroplanes that could “skip” along the atmosphere to collect air samples. “I’m confident that with a sample of the atmosphere, there could be a test that would point you toward more complex organic chemistry as well as something that could demonstrate the presence of a cell membrane,” says Blake. “There are things being sent to Mars that are doing sophisticated chemistry, so it’s not so much a limit of the technology.”

If these results hold true, it could open a whole new door to insights and opportunities. 

For Blake, the news of this latest discovery was “totally surprising” and one that could open up a huge number of opportunities for study, not only for astronomers but for biologists and chemists as well. “There’s been all this focus on the surface of Mars, and now there’s this other observation, with insights into other chemical fingerprints that we can look for,” he says.  

By learning more about life with the solar system, this work could also provide important insights on how life might originate in other places in the cosmos. “It could be plausible that an event brought life from Earth to Venus as part of a big collision on the surface of the earth,” says Blake. “Now, if we have two places in our own solar system where life exists, that really gives you a lot more information in terms of what’s going on in the cosmos. If it happens twice here, it’s likely that it’s happening elsewhere, which is really fascinating.”

Cullen Blake is an associate professor in the Department of Physics & Astronomy in the School of Arts & Sciences at the University of Pennsylvania.