Is a poisonous gas in the atmosphere of Venus a signal of life on Earth’s nearest neighbor?

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When it comes to the search for life in the solar system, Mars clearly gets most of the attention. The Red Planet seems so tantalizingly Earth-ish … if you ignore the cold, and the dryness, and the lack of all but a trace of atmosphere. After Mars, most of the attention of late has been focused on a whole series of icy moons. From Europa to Ganymede to Enceladus, it seems that both Jupiter and Saturn have a cadre of satellites that could contain an ocean hidden beneath layers of ice. These hidden seas, kept liquid by tidal heating from their giant host planets, could possibly harbor life not dependent on the sun in the same way that life on Earth may have arisen around undersea vents of warm, chemically rich water.

But in any discussion of life, Earth’s nearest neighboring planet tends to get overlooked—for pretty good reasons. Even though old science fiction stories used to posit Venus as a tropical, swampy planet swathed in clouds, in real life those clouds turn out to be composed mostly of sulphuric acid. Those clouds hover over a planet where the pressure on the surface is crushingly high, and temperatures are enough to melt lead. Far from being a lush dinosaur haven, Venus is a hellscape of heat and pressure topped off by chemical warfare.

So the news this week that another toxic chemical had been spotted high in Venus’ atmosphere may not seem like a surprise. Except … this toxic chemical may be a fingerprint of life.

Scientists have long known that the upper atmosphere of Venus doesn’t have the problems found at the surface. Go to the right level, and temperatures and pressures can be almost Earth-like. Still, there’s nothing like an atmosphere that anything on Earth could breathe, and while microbes do live at all levels of the atmosphere, it’s hard to think of a biosphere that consists only of … something … something floating above all that acid, heat, and pressure below.

However, a statement released on Monday (and leaked over the weekend) from an international team of astronomers and scientists at MIT, Cardiff University, and several other institutions shows that there appears to be the unexplained presence of a gas called phosphine high in Venus’ cloud-choked atmosphere. Phosphine is colorless, odorless, and hugely toxic to anything that breathes oxygen. It’s a relatively simple compound—an atom of phosphorus surrounded by a trio of hydrogen atoms—but on Earth, at least, it forms as a product of biological activity. 

So if the gas only comes from the action of living bacteria, and it’s present in the atmosphere of Venus … life on Venus? Eh, not quite so fast. While the scientists involved say they can’t find a purely chemical process that would sustain a trace amount of phosphine in Venus’ atmosphere, it’s already known that this gas does appear in the atmosphere of Jupiter, where it’s thought to be the result of processes that take place in the enormous pressures and temperatures low in that massive planet’s atmosphere. No processes have been identified that could produce phosphine on Venus, but clearly the gas can be generated through means that don’t involve extremophile bacteria. Also, on Earth phosphine is an end product of organic decay happening at the surface. Its presence in Venus’ atmosphere would seem to require an entire floating ecology and … what does that look like?

Still, phosphine is one of the gases that would-be exobiologists have long held up as a “biosignature” — see this gas in the atmosphere of a small rocky planet, and you have pretty good reason to think that life is involved. And the team involved seems to be seeing that gas around Venus. If nothing else, it’s extremely interesting and seems like it might justify both more direct study of Venus from Earth as well as new probes to Earth’s hot sister. 

For a while during the 1960s to the 1980s, Russia seemed about as persistent in landing things on Venus as the U.S. has been about visiting Mars. It’s a tough trip. Despite being somewhat closer than the Red Planet, getting to Venus actually takes a bit more energy rocket-wise, and when a probe arrives, any lander is facing a trip down into that high pressure heat and acid bath. 

After three Soviet failures, and one failure by the U.S., America was actually the first to get a Venus fly-by when Mariner 2 went swinging past in 1962. But altogether the Soviets made no fewer than 30 attempts to send a probe to Venus, and on Aug. 17, 1970 they actually made a landing with the Venera 7 probe, which … touched down and went quiet. That kind of failure would be a familiar pattern—Venus is a great consumer of probes—but over the years the Soviets managed to bring back a precious few images and a small amount of data from the surface informing us of just how hellish Venus really is. The last successful landing on Venus was way back in 1985, when Vega 2 touched down and survived just under an hour. A balloon it released into Venus’ atmosphere relayed data back for nearly two days.

And, strangely enough, that’s one way that bacteria might have already gotten into the atmosphere of Venus: Maybe we did it. It’s already known that some bacteria can survive a surprisingly long time in space. Probes going to Mars, dating back to Viking, go through a series of steps to make sure they don’t bring with them contaminants that could give false results in tests or even interfere with any local ecosystem. It’s unclear if these steps have been taken with probes headed to Venus because melty lead, acid clouds, etc. However, it seems extremely unlikely that Soviet probes could have carried phosphine-producing extremophiles, or that any hitchhikers could find something to eat that would have them producing phosphine 40 years later.

There are other researchers disputing the amount of phosphine identified in the announcement, and even those who accept the results aren’t exactly jumping on the “it has to be life” bandwagon. Still, it’s an interesting result that’s sure to generate more research … and if there have to be germs somewhere in 2020, a few million miles away seems about the right distance.

Is a poisonous gas in the atmosphere of Venus a signal of life on Earth's nearest neighbor? 1