Astronomers just made a huge discovery. But what does it really mean when we say we've discovered the potential for life on the second rock from the Sun? Don't go searching for aliens just yet.
Astronomers just can't keep a secret.
My favorite example of this was the 2016 landmark discovery of gravitational waves. A press conference was announced so that the whole world (outside of existing collaborators, of course) could learn together that physicists had discovered a new way of observing the universe. But 16 minutes before the conference, an astronomer tweeted a picture from a NASA celebration planned to coincide with the information’s release. It was a photo of a cake with a celebratory message scrawled out in sugary green icing: “Here’s to the first direct detection of gravitational waves!”
The secret was out.
To be fair, this discovery was huge. The existence of gravitational waves had been predicted for over 100 years. The Laser Interferometer Gravitational-Wave Observatory (LIGO) is so far the largest investment the National Science Foundation has ever made. So, you know, detecting gravitational waves was definitely worth a celebratory cake.
And astronomers had been abuzz about a possible revelation of gravitational waves for weeks. We noticed that one by one, all of our major telescopes had been directed to one spot on the sky … presumably to follow up on a source of great interest.
Is there life on Venus?
Astronomers found signatures of phosphine, a molecule that may be produced by some form of microbial life, in Venus's atmosphere.
So, it's no surprise that the night before the press embargo was lifted on the recent news from Venus, astronomers—and anyone who follows astronomers on Twitter—already knew what was coming: There were signs of life from our next-door neighbor.
Well, at least that’s what you would think if you read only the headlines. The reality is a bit more subtle. Astronomers found signatures of phosphine, a molecule that may be produced by some form of microbial life, in Venus's atmosphere. Or not.
What is phosphine?
A phosphine molecule is the combination of one phosphorous atom and three hydrogen atoms. Here on Earth, we consider phosphine to be pretty toxic. It’s an explosive, corrosive, and hazardous gas used as a fumigant or in the preparation of flame retardants. As if to cue our brains to stay away, it smells like garlic or decaying fish when concentrated.
Phosphine is produced by bacteria
Phosphine can be prepared in a laboratory, but it’s also produced by bacteria. We don't completely understand the details of how bacteria produce phosphine. But we do know that the gas is produced by anaerobic bacteria.
Anaerobic bacteria thrive without oxygen. Much of Earth's history was anoxic, meaning "without oxygen." In fact, it's under those anoxic conditions that we believe life on Earth first formed.
Why is that important? Because when astronomers (like Dr. Clara Sousa-Silva, one of the authors of the new Venus study who goes by @DrPhosphine on Twitter) go looking for signs of life, they don't just look for things like radio signals from intelligent life. They also look for chemicals, like phosphine, as signs of the precursors to intelligent life.
Is there bacteria on Venus?
So, could the bacteria that produce phosphine be living on Venus?
Venus is terrestrial like Earth—a rocky place with an active mountainous, volcanic surface. It's also similar in size. It's the second rock from the Sun while Earth is the third. But despite the similarities, there are dramatic differences between Venus and Earth.
Here are a few other fascinating facts about Venus. It spins in the opposite direction from Earth—the Sun rises in the west and sets in the east. The planet also rotates very slowly, so a single day on Venus takes 243 Earth days. Winds there consistently blow at hurricane force.
To say the surface of Venus is a pretty harsh place is an understatement. Not only is the pressure 92 times the pressure at sea level here on Earth, but its thick atmosphere traps heat at the surface—a runaway greenhouse effect—for an average temperature of 867 degrees Fahrenheit (464 degrees Celsius). That’s hotter than the surface of Mercury, despite the fact that Venus is much farther from the Sun.
The surface of Venus has an average temperature of 867 degrees Fahrenheit (464 degrees Celsius). When we get excited about a potential sign of life, we’re not talking about life like us.
But as you move away from the surface, the pressure and temperature decrease. At about 31 miles (50 kilometers) up, conditions are almost Earth-like. (Well, perhaps “almost” is a stretch. The atmosphere on Venus is still about 80% sulphuric acid.)
So, here's an important point: When we get excited about a potential sign of life on Venus, we’re not talking about life like us. We’re talking about microbial life, like the extremophile species that thrive in the most extreme environments our planet has to offer.
Is there phosphine on other planets?
Phosphine is produced inorganically (without the help of bacteria or other lifeforms) in the atmospheres of Jupiter and Saturn, but the conditions that allow for its creation there aren’t the same as the conditions on Venus.
The gas forms in the high-temperature interiors of Jupiter and Saturn and reacts with other molecules in their turbulent atmosphere. All of this takes incredible amounts of energy—energy potentially drawn from the violent convective storms that occur on gas giant planets. But such a process would be an incredibly inefficient explanation for the source of Venus’s phosphine.
Where do we go from here?
Phosphine is a very dangerous gas here on Earth, so it's not well understood. There could be inorganic processes creating phosphine that we just haven’t conceived of yet. So the presence of phosphine on Venus doesn't mean there's life on Venus, just the newly discovered potential for it.
Our next step should be to send a direct probe.
Back in the 80s, astronomers thought there might be signs of something peculiar going on in the atmosphere of Titan, Saturn’s largest moon. There was oxygen in the atmosphere, and its existence couldn’t be explained through any of the regular methods. Twenty-five or so years later, astronomers figured out, thanks to the Cassini spacecraft, that a neighboring moon, Enceladus, spews water vapor into space that makes its way over to Titan and reacts with other molecules there to form oxygen.
To really understand the source of the phosphine on Venus, and the rest of the complicated Venusian cloud chemistry, our next step should be to send a direct probe. The last spacecraft to enter the atmosphere of Venus was the Soviet Vega 2 probe, which operated for two days there in 1985.
Just don’t tell Percy, the Mars Rover, that we’ve started looking the other way.