Extraordinary Claim: Life on Venus?
Extraordinary claims require extraordinary evidence, scientists like to say. One smelly molecule is not enough to claim life.
The whole business of astrobiology is to find life in space. Without the bio, it’s just astrology (17 Dec 2014). Most announcements about possible life come and go like bright meteors that make a brief flash and are quickly forgotten (9 Aug 2019). The current flashy story buzzing around the Big Science News concerns a putative biomarker in the clouds of Venus. This time, though, the believers are saying that the researchers tried really hard to rule out non-biological causes. One of them concludes, with Sherlock Holmes, that “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.” But is that the case? There are always unknown unknowns that can mislead experts.
The focus is on the compound phosphine (PH3), a smelly, explosive, poisonous gas (PubChem) found in rotting fish and penguin poop. As far as scientists believe now, it only is produced by bacteria and biological processes. It also oxidizes fairly quickly, so to find significant amounts in the cloud tops of Venus, there must be a source that replenishes it constantly. But Venus is a complex planet with strange chemistry and lots of heat and possibly volcanic energy. Who knows what is going on there?
Here’s a sample of the hype going around the media echo chamber:
Daily Briefing: ‘Unexplained’ molecule on Venus hints at life (Nature). “Phosphine has been detected in Venus’s atmosphere, raising the thrilling question of whether the molecule might be a sign of life on the planet.”
Have we spotted alien life floating in the clouds of Venus? (New Scientist). Leah Crane uses a titillating headline with the power of suggestion. Up goes the perhapsimaybecouldness index: “There are no known non-biological mechanisms of making the gas on Venus, so it may be being produced by alien microbes.” Breathlessly, she ups the ante:
Only two scenarios remain: either there is something going on in Venus’ clouds that we don’t understand, or whatever is producing all that phosphine is alive.
“It’s basically either not a big deal, or we just found Venusians and that’s incredible,” says Sousa-Silva. “The fact that it’s even a possibility is really breathtaking to me.”
It’s not true that “only two scenarios remain.” Philosophers of science can prove that for any data set, there are an infinite number of theories able to explain it. Scientists might respond that only two are reasonable. But how reasonable is it to theorize that bacteria arose by chance within the toxic clouds of a hellish planet? That idea should be ruled out of court from the start.
Is there life floating in the clouds of Venus? (BBC News). Jonathan Amos employs the suggestive headline tactic, too. “It’s an extraordinary possibility – the idea that living organisms are floating in the clouds of Planet Venus.” Oooh. Aaah. Only at the end does he try the reality check: “Why should we be sceptical?” He points out that any organisms in the clouds would need armor to escape the sulfuric acid. He quotes one scientist who doubts the claim: “I think that life in Venus’ clouds today is so unlikely that we’ll find other chemical pathways of creating phosphine in the atmosphere – but we’ll discover lots of interesting things about Venus in this search.” Nevertheless, Amos ends with the illogical conclusion that if life can survive on Venus, “it means maybe life is very common in our galaxy as a whole.” No, it doesn’t. His “maybe” gives him an escape: “maybe” cows can jump over the moon.
Venus: could it really harbour life? New study springs a surprise (The Conversation). One would hope that astronomer Monica Grady, looking at this claim from the outside, would bring some epistemic modesty to the breathless media mob. She knows that a similar claim was made about Mars. But she understands how the bio-astrology game is played. To find out if there is life on [name planetary body], we need more funding!
The presence of methane as a biosignature in Mars’ atmosphere is still hotly debated. It may be that astrobiologists searching for life beyond Earth now have an additional atmospheric biosignature about which to argue.
The European Space Agency is currently considering a mission to Venus that would determine its geological and tectonic history, including observation of potential volcanic gases. This would yield a better idea of the species that are added to Venus’ atmosphere. The new study should boost the case for selection of the mission.
Possible hint of life discovered on Venus (Live Science). Rafi Letzter catches his breath and presents less hype and a little more balance; his emphasis is that we just don’t know what’s going on in the cloud tops of Venus. He does not rebuke the hype, though, and his headline still uses the power of suggestion.
Update 11/26/2020: Never mind. Science Magazine says that the scientists are giving up on the claim. “Potential signs of life on Venus are fading fast,” Paul Voosen writes. The interpretation of phosphine is a tiny blip on the spectrum (1 part per billion or less), and could be due to non-biological chemistry.
Good Science Should Exercise Restraint
The image of the calm, rational scientist is gone. Wild speculation is in. Consider this whopper of a headline by Brian Koberlein at University Today: “Could there be a form of life inside stars?” A science news site should be embarrassed to suggest such a Trekkie myth, but he actually entertains the idea with some seriousness, accompanied by a picture of the Star Trek Enterprise, too. This is the kind of pure clickbait some reporters engage in.
Given what we know about Venus (hot surface, sulfuric acid in clouds, possible volcanoes), the idea of life there is almost as absurd as the idea of nuclear life inside stars. Intelligent design scientists keep trying to get secular scientists to admit what they should already know: even the simplest life we know of is extraordinarily complex, made of molecules that can only exist in a narrow range of conditions like those on Earth. Even on the privileged planet for life, hypothetical “protocells” must meet minimal requirements for metabolism, genetics and storage. Each one of these specifications is highly improbable. Together (and they must occur in the same time and place), they rule out the chance origin of life.
Even if by some wild, extremely unlikely circumstance the phosphine at Venus turns out to be biogenic, the simplest hypothesis should be to test if the clouds became contaminated by Earth microbes. Planetary scientists already know that transfer of material between bodies does occur; there are Martian meteorites in Antarctica. Science should consider known causes before even thinking about bio-astrological miracles.
The phosphine measurements should motivate research to learn about unknown chemical pathways that produce phosphine. Letzter quotes one scientist who says, “the photochemistry of Venusian cloud droplets is almost completely unknown.” The proper response by scientists, then, should be to learn about phosphine and run experiments in the lab in Venus-like conditions, instead of running to the press with teasers about Venusians. Doing it to get funding for space missions is disingenuous.
Scientists used to value “epistemic modesty,” which means that conclusions or suggestions should never outrun data. In the fields that concern origins, that value has been tossed to the wind. From our experience, we know that occurred when King Charles launched his GSS (Great Society for Storytellers).