The Quebec scientific community wants to be ready. If telescopes detected a unique chemical signature in an exoplanet’s atmosphere, could we say that there is a trace of life there? Physicists, philosophers and biologists met on Monday at the 90th Acfas Congress to discuss it.
“Imagine you are some distance away in space and looking at the earth. Can you know if there is life on this planet? asks astrophysicist René Doyon, director of the Institute for Research on Exoplanets and professor of physics at the University of Montreal, at the opening of a symposium on the origin of life.
In December 1990, the Galileo spacecraft, sent to study Jupiter, aimed its mirror at our blue planet. The abundance of oxygen gas, the odd presence of methane (from cow digestion), and the “spike” of red light absorption (related to photosynthesis) signaled the presence of life on Earth. The proof was there…
But what about the worlds we know next to nothing about and that are light years away? We already know 5000 exoplanets. We know there are billions of them in their star’s habitable zone. The “biosignatures” revealing the presence of a gas in the atmosphere of these candidates will not be unequivocal. Oxygen is not synonymous with life. A good dose of interpretation will be essential to confirm that extraterrestrial microbes are involved.
It will be “very controversial” when the first scientists say life has been found elsewhere, warns Mr Doyon. Only when the same pattern is discovered on multiple Earth-like exoplanets — which is unlikely to happen with the James Webb Telescope, which has been in operation since last year, but with its successors — can the community start untangling its tongue, he says.
But what exactly is the life we seek? The philosopher of science Frédéric Bouchard of the University of Montreal suggests to his colleagues gathered at Acfas not to lock themselves into a restrictive, ill-defined and wrongly limited to life as we know it notion revolving around carbon, water and oxygen .
“Increase solar irradiance by 10% and the organization of complexity on Earth would be radically different from what we know today,” says Bouchard. It’s not a bad guess looking at those signatures [l’oxygène et le méthane, par exemple]. We can start there for logistical reasons, but we also have to look for other complex behaviors. »
Extremophilic yeasts
Everything that lives evolves. But is everything that evolves in response to environmental stress alive? Not necessarily. Evolution by natural selection can exist outside of the traditional framework of biology as we know it, says philosopher Bouchard.
An example in a solar system close to you: In the atmosphere of Venus, current instruments show the presence of “a chemistry that we do not understand,” says astrophysicist Étienne Artigau of the University of Montreal. The complex photochemical reactions taking place there may suffice for a liberal definition of life. Missions planned for the 2030s will see.
Another mission, Dragonfly, will visit Titan, an icy moon of Saturn that is also suspected to have very complex chemical reactions. “If we see a molecule splitting in two,” and in a sense replicating itself, “what are we writing on the front page of the New York Times? asks Herr Artigau. Are we saying that we have found life elsewhere than on Earth?
Among the speakers was also Carla Bautista, PhD student in biology at the University of Laval, who studies the adaptation of organisms to extreme conditions: salinity, radiation, acidity, temperature, pressure, etc. It is in these extraordinary environments that we imagine life.
In her laboratory, Ms. Bautista grows yeast under UV lamps. Yeasts develop at breakneck speed: in a month you can see how 100 generations follow each other. With this, the researcher is testing the “limits” of the adaptation of these organisms. And through the association, she hopes to show more general boundaries of life.
If astrophysicists find a good planet candidate, the young researcher could test her yeast under UV radiation equivalent to that of this space world. “Of course you can only test life as you know it,” she says. But at least one can get useful information about the limits of adaptation to stress conditions with these experiments. »
Extraterrestrial life can hold its own: Quebec scientists are waiting for it.