If you’ve been following space-related news over the past few weeks, you might have noticed some headlines about astronomers getting very excited about the possibility of life not on Mars, but on Venus. The discovery of phosphine in Venus’s atmosphere is a significant one, but there are lots of questions still to answer.
Is there life on Venus?
In the early days of planetary exploration, people speculated about whether we might find life beneath the thick clouds of Venus. By the time the first Soviet space probes landed on the planet, this idea seemed to have been put to rest.
Though Venus is similar to Earth in size and composition, its thick atmosphere and high pressures make the surface inhospitable to life. In fact, despite Venus being the second planet from the sun, after Mercury, a runaway greenhouse effect makes Venus’s surface the hottest of any planetary body in the solar system.
With temperatures high enough to melt lead and an atmosphere that rains sulfuric acid, Venus seems one of the least likely places to find life in the solar system. Accordingly, for the past decades the search for life in our solar system has shifted to Mars. However, the assumption of a lifeless Venus is now called into question with the detection of phosphine, an important biomarker, in the planet’s atmosphere.
What’s a biomarker?
As astronomers have discovered thousands of planets around other stars and it has become feasible to even detect gasses in these distant atmospheres, scientists have worked to determine what chemicals might be signatures of life. For example, the detection of oxygen and water vapor in a planet’s atmosphere could hint at conditions that would make life possible. But other chemicals, known as biomarkers, as far as we know are only produced by biological methods.
Phosphine, for example, which is composed of one phosphorus atom and three hydrogen atoms, is not produced by any natural methods that we know of other than life processes and industry. This means that if phosphine was detected in the atmosphere of a distant exoplanet, it would be a strong indication that life or possibly even technology was present there. This made it all the more surprising when phosphine turned up not in the atmosphere of a distant exoplanet but in the atmosphere of the seemingly inhospitable planet next door.
How was the phosphine detected?
Phosphine gas was first detected in the clouds of Venus by the James Clerk Maxwell Telescope, a radio telescope on the summit of Maunakea, Hawaii. Chemicals absorb different types of light, and this absorption pattern is unique for each chemical, like a fingerprint.
When sunlight reflects off Venus’ clouds, the fingerprints of different chemicals are embedded in the reflected light and can be detected by instruments on Earth. For confirmation of the observation, the massive dishes of the ALMA observatory high in the Atacama Desert in Chile swung to focus on Venus. Part of the array of telescopes that took the first ever direct image of a black hole, these powerful telescopes confirmed the detection.
So, does Venus have life?
Since we’re largely certain there is no industrial society hidden beneath Venus’s clouds that could produce the phosphine, its presence hints at the possibility of simple life in Venus’s atmosphere. Though Venus’s surface is hellish, higher in the atmosphere, the temperatures are mild, and there is even water vapor present.
Recently, scientists proposed and modeled an entire hypothetical life cycle for simple organisms that could live their lives suspended in these clouds. The presence of large amounts of sulphuric acid isn’t necessarily a deal-breaker for life either, as there are several forms of life here on Earth that thrive in similarly extreme conditions.
Why could this discovery be so important?
Like Mars, planetary geologists believe Venus was more Earth-like in the past, complete with surface oceans. A cataclysmic event resulted in a runaway greenhouse effect that transformed the planet into the inhospitable place it is now. But if biological matter, even single-celled organisms, remain, this would indicate that life could be common throughout the universe.
Every nook and cranny that we examine on Earth is filled with microscopic life, but, so far, we have no way of knowing if that’s unique to Earth or to the solar system as a whole. As with the detection of simple life on Mars, biological markers on Venus would transform our understanding of the origins of life.
But does phosphine mean we’ve actually discovered life on Venus?
At this point, no. There may be unknown natural processes that create the amount of phosphine detected without the presence of life. We simply don’t know yet.
Of course, that’s one of the things that makes this discovery so exciting: it’s the possibility of life, and it changes the way we view our planetary neighbor. If phosphine had been discovered in the atmosphere of a planet light-years away, all we could do was wonder. But now scientists can begin planning the next steps of investigating the chemical footprints of life on Venus.