Colby Cosh: Life on Venus? Probably not

The question remains open. But the initial media hype over the result obviously went much too far, as it always does

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Life on Venus is on the ropes. In September, you may recall, an international research team announced that they had analyzed spectroscopic images of the upper Venusian atmosphere and found absorption lines corresponding to the presence of phosphine — the PH3 molecule, which takes the form of a toxic gas that can self-ignite in air and is said to smell like rotten fish.

When light (or other electromagnetic energy) passes through any chemical, the chemical swallows up some colours and emits others; this allows us to read the “fingerprint” of a gas in the atmosphere of a distant planet. (It’s also why different gases in a “neon” sign create different colours.)

The phosphine finding made international headlines because other gases in the Venusian atmosphere should attack and degrade phosphine easily. If the stuff is there, something must be emitting and constantly replenishing it — and no one can think of a geological (venological?) process that would accomplish this.

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Earth’s atmosphere has small amounts of phosphine created by decaying organic tissue. Jupiter has phosphine, but Jupiter is a stormy gas giant that easily accommodates the large volumes of energy needed to build phosphine from elemental phosphorus. Phosphine on a small rocky planet, the story goes, is a strong reason to suspect the existence of biology there.

You will notice that this is an “unless there’s something we haven’t thought of” hypothesis right out of the gate. Phosphine isn’t decisive evidence for extraterrestrial life, just a good reason to explore further. But the September paper, whose principal investigator is the celebrated Cardiff University astronomer Jane Greaves, met with an unfriendly initial reception.

Venus is easy to pick out in the sky, but even our planetary neighbour doesn’t present a very big cross-section to telescopes or spectroscopes. Any signal we receive on the ground has passed through our own atmosphere, requiring statistical corrections, and the “fingerprints” of different chemicals can interfere with one another. Also, a spectroscopic image of a planet is taken through a long slit, which has to be passed or scrolled over the cross-section of the planet’s disk, so there’s lots of three-dimensional geometry involved in interpreting the results.

Analyzing Venus’s atmosphere from Earth is like finding needles in a haystack, except the haystack is 100 metres away and on fire. (Which is probably possible!) Flipping through the artillery duel between Greaves and her critics — themselves belonging to several tribes — has brutalized me into overcoming my resistance to cliché and resorting to these words: “Looks like it’s more art than science.” One group thinks her phosphine is just sulphur dioxide, which there’s plenty of on Venus. This seems to boil down to a contest of statistical models, themselves chosen on slightly esoteric and even idiosyncratic grounds.

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But Greaves’s group has certainly retreated some distance. It seems to be agreed between the duellists that the original paper had flaws, created in part by the teams operating the spectroscopic instruments. There was a wrong flag setting in computer coding here, an inappropriate detrending method there.

The Greaves team has had to reduce its overall estimate of the quantity of phosphine in the Venusian atmosphere from about seven parts per billion to more like one. The team also thinks the remaining result, although weakened in magnitude, is more reliable statistically than before. But like a heretic appealing to a future council of the church, they are willing to defer final judgment until further passes of Venus’ disk are made, using the full range of available instruments.

Procedurally, the lay observer of science will say this looks a lot like the early days of a dud hypothesis. When someone says they’ve found 60 unicorns, and in a matter of weeks they’re acknowledging problems but insisting they’ve still got six unicorns, you know which way to bet. Especially if there’s the promise of a glamorous unicorn-hunting space mission lurking as a spur to the imagination.

The less phosphine we end up seeing in the Venusian atmosphere, the more likely that potential abiotic explanations for its presence become. It’s the Rumsfeld doctrine: phosphine itself, in nature, involves unknown unknowns. But Greaves hasn’t suffered a decisive reverse, either. In her reply to critics I detect some snark about how her group has been more open about modelling methods than the people throwing mud at her phosphine inference.

So the question remains open. But, meta-news flash: the initial media hype over the result obviously went much too far, as it always does.

National Post
Twitter.com/colbycosh

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