Source: Wired.com

It sounds ridiculous, bizarre, even stupid. Life on Venus, the hottest planet in the Solar System? This is a world often regarded as Earth gone wrong, where extreme climate change has turned it into one of the closest approximations of hell we’ve ever seen. And now we’re told it might be home to alien life. It’s a discovery that if proved true would have profound consequences for how we view our place in the universe. The only problem? Proving it.

The idea of life on Venus is not new, and dates back to at least the 1960s when the late American astronomer Carl Sagan discussed the possibility. “If small amounts of minerals are stirred up to the clouds from the surface, it is by no means difficult to imagine an indigenous biology in the clouds of Venus,” he wrote in a paper in Nature in 1967.

Now, more than five decades later, scientists have discovered phosphine on Venus. Phosphine – a compound of phosphorous and hydrogen – is thought to be a potential biomarker. In other words, we know it can be produced by life, and its detection hints at biological production.

“[We tried] to iterate down the list of options to explain the phosphine being present,” says Sukrit Ranjan from Massachusetts Institute of Technology, a co-author on the discovery paper in Nature Astronomy. “All of that has come up short. So we’re left with things we have not yet fully ruled out. That includes chemistry and biology that we don’t know about yet.”

Phosphine can be produced by a number of non-biological processes. These include geological sources like volcanic activity, or even extreme pressure environments where hydrogen is squeezed together – such as on Jupiter and Saturn. On Earth, phosphine is also produced by certain anaerobic microbial life, which requires little oxygen. Similar extreme life forms could, maybe, have made their home in the Venusian clouds.

“This discovery is incredibly exciting,” says Sarah Rugheimer from the University of Oxford, whose research involves looking for life on exoplanets, worlds beyond the Solar System. “It’s either a chemistry that’s really different and unusual, or it’s life.”

The discovery was led by Jane Greaves from Cardiff University, using two telescopes on Earth – the James Clerk Maxwell Telescope in Hawaii and the Atacama Large Millimetre/submillimetre Array (ALMA) in Chile – to observe a signature of phosphine in radio observations of Venus.

Its presence, in the atmosphere of Venus, 50 kilometres above the surface, is believed to be in a region that could be hospitable to life, outside of the hellish conditions on the surface of the planet where high temperatures and pressures render life as we know it unthinkable.

Before we even begin to consider the possibility of its production by life on Venus, however, there are a number of hoops to jump through. First, other astronomers will need to try and reproduce the results, using the same or other telescopes, to check if the phosphine is really there. Astronomers will then want to conduct further experiments to investigate ways that phosphine can be produced, and see if they can rule out non-biological processes. “[We need] lots more laboratory studies [and] calculations to nail down some of the fundamental parameters,” says Ranjan.

After that, we could consider sending missions to investigate the phosphine in more detail, perhaps even one day looking for life itself on Venus. But it will likely be a very cautious progress until we get to that point. There are already a number of missions to Venus on the drawing board. Nasa is considering two proposals to the planet, DAVINCI+ and VERITAS, the former of which would include an atmospheric probe that could possibly look for gases like phosphine. Several other missions are also in the works. India plans to launch a mission this decade, while Russia has long talked about sending a spacecraft there, having led much of the previous Venus exploration in the 1970s and 80s. Europe, too, is considering a mission called EnVision in 2032.

Many of these missions, however, are designed with other goals in mind – such as mapping the surface of Venus, or looking for volcanic activity. In order to look for life, if it were really there, we would need a new type of mission. “Ultimately we will want to sample the atmosphere, and get that sample back to test it,” says Richard Ghail from the Royal Holloway University of London, the lead on the EnVision proposal. “That means some sort of balloon with a sample return [capability], or a large enough balloon with some of the kit on it.”

Such a mission would likely be years or even decades away, but in the more near-term, there are things that could be done. The US private company Rocket Lab hopes to launch a small mission to Venus as soon as 2023, which would include an atmospheric probe, and the company is looking into what small instruments it could include that could look for life.

Scientists will also want to continue studying the atmosphere of Venus from Earth, not only to independently confirm the presence of phosphine, but to investigate the different processes that can produce it back here in laboratories.

If, after all of these studies, the signs continue to point to life, then we can begin to wonder what sort of life that might be. At the moment, it’s thought this would be some sort of airborne microbe in the Venusian sky, living in droplets originating from the planet’s thick clouds.

“Our best guess is some sort of microbial life living in the cloud droplets,” says William Bains from Massachusetts Institute of Technology, who was also a co-author on the paper. “The chances of there being life on the surface are spectacularly small. This is much more likely to be in the clouds.” We do know there are airborne microbes on Earth, so if the conditions are just right on Venus, there’s an alluring possibility they are present there too.

Conditions on Venus are not ideal. These droplets would get extremely hot as they fell from the sky, killing any microbial life present. Instead, it might be that the droplets are in a continuous cycle of evaporation and falling, with microbes clinging along for the ride. “You have a cycle operating in the clouds,” says Bains, who also says that perhaps even some of the droplets would fall to the surface, although it’s unlikely any life would survive that journey. “It would be baked into charcoal-like stuff,” he explains.

It’s a tantalising possibility but for now it remains just that. If the phosphine discovery holds up, and we can’t explain it via non-biological processes – which most scientists would agree is still the most likely outcome – then things could get very intriguing.

Venus has long been overshadowed by other more alluring targets in the search for life, such as Mars or Jupiter’s moon Europa. Now, with this phosphine discovery, our Solar System’s own version of hell could find itself at the top of the list. “It will probably take more than a decade to hammer down what’s happening,” says Rugheimer. “Phosphine is very interesting as a bio-signature. It’s just coming from one of the places we would least expect life.”

Source: Wired.com