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So, life on Venus?

We have been dreaming of finding alien life on other planets. Perhaps we don’t have to go far. Scientists found a special type of gas on Venus. Its origin being unknown, the gas could point to the presence of microbes in Venus’s atmosphere. Could.

ooo

I remember reading a novel Between Planets as a teenager. Written by Heinlein, the master of science fiction, the story follows a boy on his voyage from Earth to Venus, where he gets caught up in the Venerian1I think the proper adjective is “Venusian”, but Heinlein uses “Venerian”. war of independence. The swamp-covered planet is home to a deceptively slow and dull species of Venerian dragons. I enjoyed this coming of age story set on another planet. I imagined the sluggish tentacled creatures fighting alongside human settlers, and rooted as they defeated the fascist Earth. Nevertheless, something bugged me. As much as I tried, I couldn’t set aside the fact that the depiction of Venus was all wrong.

Venus and Earth have similar sizes and masses, which is why they are sometimes called “sister planets.” After scientists established that it had an atmosphere, they started to speculate that Venus was habitable; it might be a bit warmer than Earth, due to its proximity to the Sun, but it could still be a place where humans could live. Naturally, science fiction picked up the premise, and the “Venusian” genre reached its peak between the 1930s and 1950s. Then the scientists brought the writers and the general public back down to earth2Sorry for the bad pun.: Venus was anything but habitable. It was hell.

venus
Has life been hiding on this planet all along? Credit: Kevil Gill/JAXA/ISAS/DARTS
On Venus, the incredibly dense atmosphere presses upon the surface, the out-of-hand greenhouse effect creates temperatures as high as 460 degrees Celsius, and the frequent storms produce acid rain. The rotation of the planet is peculiar as well. Most planets rotate in an anti-clockwise rotation, while Venus rotates clockwise; if you were able to look through the thick Venusian layer of clouds, you would see the Sun rise in the west and set in the east. To top it off, a day on Venus lasts 243 Earth days. It is difficult to imagine that life as we know it could exist on such a planet.

Yet, scientists just informed us that they possibly discovered life on Venus. What did they find that gave them the confidence to make such a remarkable claim?

Phosphine may be a good tracer of life if detected on exoplanets or bodies in the Solar system. Credit: NASA, edited by MIT News.

The core of the discovery is phosphine, a molecule made of one phosphorus and three hydrogen atoms. Phosphine is one of the stinkiest and most toxic gases on Earth, found in swamps and bogs, and highly flammable. Oxygen-breathing (or aerobic) life on Earth wants to have nothing to do with it. But, while not prevalent, anaerobic organisms have more tolerance for it. Researchers found that microbes and bacteria that don’t breathe oxygen can produce phosphine. And since they couldn’t find another way to create this molecule, phosphine became a contender for the best sign of life to look for on other planets.

There is another way to produce phosphine. Phosphorate and hydrogen don’t like each other that much, and a lot of energy is needed to smash them together and form a molecule. The molecules exist in the atmospheres of Jupiter and Saturn. In the hot giants’ bellies, the molecule likely arises because of the abundance of hydrogen, high temperature, and high pressure. Under the conditions on Venus the phosphine can’t form in the same way. Rocky planets, such as Venus, are the best place to search for phosphine produced by life forms.

Phosphine signature in the spectrum of Venus's atmosphere. Greaves et al. 2020

And now researchers found the phosphine on Venus3Fun fact. In the past, Venus was often mistaken to be two different celestial bodies, namely morning and evening star. The Greeks referred to the morning star as Phosphoros, meaning light-bringer. I mean, that is quite a coincidence!. They used the ALMA telescope array in Chile and the James Clerk Maxwell telescope on Hawaii to observe the planet’s atmosphere. They found the signatures of the toxic molecule, its abundance being too high to be explained by any known phenomenon in Venus’s atmosphere. Does that mean that Venus’s atmosphere hides little green men microbes?

The first response of everyone, as the authors admit themselves, should be skeptical. This is such a big claim, with such profound consequences, that it shouldn’t just be believed. We still remember the detection of faster-than-light neutrinos, right?4At least alien life form on Venus wouldn’t break the physics.

Saturn’s moon Titan also serves as a lesson. Astronomers discovered carbon monoxide in Titan’s atmosphere in the early 1980s. For nearly three decades, the origin of the gas remained a mystery. Then a key new piece of information provided a solution: Enceladus, another Saturn’s moon, was shooting water into space, some of it eventually ending up on Titan. Once the scientists took that into account, their models explained the observed abundances of carbon dioxide and other gases. In other words, maybe there is a chemical process at play in the Venusian atmosphere that we don’t know yet.

The conditions on Venus are harsh. The ground is scorching hot. The extensive network of thick clouds is highly acidic—we don’t know of any organism on Earth that could survive that. But in the upper cloud layers, about 50 kilometers above the ground, the temperature and pressure aren’t that much different from that on Earth. And acidity becomes more manageable as well. Perhaps some life could survive there. Perhaps there once was life on Venus, before the greenhouse effect turned it into today’s inhospitable place. Perhaps some of that life adapted, escaped into the upper layers of the atmosphere, lived in the permanent clouds. Perhaps.

Astronomers will scrutinize Venus, trying to confirm the results. Chemists and astrobiologists will try to understand phosphine even more—is there another way to produce it? Or is it just that we don’t understand the conditions on Venus well enough? If these questions remain unanswered, or they all point to alien life forms as the most plausible explanation, then a mission can be sent to Venus to look more closely at the atmosphere and perhaps to gather samples. Indeed, it is fantastic that we found phosphine on Venus. If we found it on an exoplanet, we could never confirm our hypothesis for sure. But Venus is close, and we can quite easily go there.

Aliens or not, we have every reason to assume that we will know the answer eventually. This is what makes the discovery so exciting.

But I doubt we will find Venerian dragons.

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