On the surface (you’re welcome for the joke), Venus isn’t even close to being hospitable to life. But that’s not the end of the story.
This planet has by far the hottest surface temperatures in the solar system, beating out even Mercury, even though Venus is twice as far away from the Sun. That’s because of a runaway greenhouse effect which unfolded…eh, we’re not exactly sure, but somewhere between a few hundred million and a few billion years ago – there’s a debate here. But it doesn’t matter when exactly for our purposes; what matters is that it happened, and now the planet is choked to death in its own noxious atmosphere, with atmospheric pressures at the surface over 900 times greater than the Earth at sea level.
So super high pressure, and temperatures anywhere from 900 degrees Fahrenheit (480 Celsius) on the high end to a balmy…847 Fahrenheit / 450 Celsius on the cool end.
Here’s the thing. There is no version of any kind of life in any form that we can possibly imagine existing under those conditions. I know that the universe is larger than our imagination, and there’s always room for surprises, but…phew, even that’s stretching it.
No, where we’re really interested with Venus is in its atmosphere. The higher up you climb in altitude, the cooler the temperatures, until you’re all the way in space, which is also bad but in the opposite way as the surface. But right in the middle, at an altitude between 50 and 60 kilometers, the temperatures are….fine. Comparable to the range of temperatures that we see on the Earth. And the air pressures are…fine. Comparable to the range of pressures that we see on the Earth.
The atmosphere itself is…not so fine. It’s mostly carbon dioxide, which hey, it’s what plants crave, but also a lot of nitrogen. And ultraviolet radiation breaks down the molecules in the upper atmosphere to make a host of really, really nasty stuff, like sulfuric acid, hydrogen sulfide, and chlorine.
So yes, you could walk outside and breath the air, and it would dissolve you from the inside out.
Life in the atmosphere of Venus has to have a really strange biochemistry. And in September of 2020 a group of astronomers claimed to detect the presence of large quantities of phosphine in the Venusian atmosphere. Now phosphine is an interesting molecule. It’s quite stinky, and on Earth it’s a byproduct of anaerobic bacteria (which is part of the reason that marshes and swamps are less than pleasant places to visit).
There ARE ways to produce phosphine without bacteria, and in fact Jupiter makes loads of it all the time, because of that planet’s super-high temperatures and pressures – properties that Venus lacks. PLUS phosphine breaks down easily in UV light, so for it to be present in great quantities means that it has to be actively replenished and produced.
Cue…a giant mess. The news caused a tremendous uproar, with outlets around the world picking up on the tantalizing possibility. But then those pesky OTHER scientists shot back, arguing that the original research was flawed and used an improper analysis of background noise. Then the original authors updated their results and doubled-down. Then the astronomers working the telescope itself chimed in. Then others claimed that the signal was just getting confused for sulfur dioxide. Then…
Like I said, a giant mess, that even today isn’t fully resolved. From what I can tell from the literature, the general stalemate sort-of-community-consensus that Venus probably doesn’t have phosphine, and if it does, it’s at levels far lower than the original claim.
Case closed? Not quite. NASA is developing two – that’s right TWO – Venus missions to investigate further, because honestly there’s only so much we can get from remote observations and the small scattering of probes we’ve (and by that I mean the Soviets) have been able to squeeze down to the surface for short-term visits.
One mission is DAVINCI, which will be an orbiter and an atmospheric probe. The other is VERITAS, an orbiter designed to map the surface in high resolution (which will also tell us a lot about the atmosphere). Don’t worry, both missions have been delayed because NASA is kind of going through a thing at the moment.
The prospects of life on Venus seem rather low. But it’s not zero. And long ago, before the greenhouse catastrophe, Venus was likely very similar to Earth. After all, we’re made from the same material and have very similar properties – it’s not an outrageous stretch of the imagination.
And some strange form of life may have gotten a start and evolved to adapt to the changing climate. Venusian life couldn’t use water, it’s way too hot for that. But they may use droplets of ammonium sulfite or sulfuric acid dispersed through the Venusian clouds. This life would be extremely simple, perhaps even lacking cell membranes and just consisting of self-replicating molecules that use UV radiation as an energy source.
This life may alter the chemical composition of the Venusian atmosphere, explaining several mysteries like the extra oxygen in the cloud layers, and extra amounts of sulfur dioxide where it shouldn’t be based on simple chemical models.
I suppose it’s worth a closer look after all.