The Quebec scientific community wants to be ready. If telescopes were to detect a unique chemical signature in the atmosphere of an exoplanet, could we say that there is a trace of life there? Physicists, philosophers and biologists met Monday at 90e Acfas Congress to discuss it.
“Imagine that you are at a good distance in space and that you are looking at the Earth. Would you be able to 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, opening a symposium on the origin of life.
In December 1990, the space probe Galileo, sent to study Jupiter, turned its mirror to our blue planet. The abundance of gaseous oxygen, the strange presence of methane (from the digestion of cows) and the “spike” of absorption of red light (associated with photosynthesis) signaled the presence of life on Earth. The proof was there…
But what about the worlds we know next to nothing about that are light years away? Already, we know 5000 exoplanets. We know that there are billions of them in the habitable zone of their star. The “biosignatures”, which reveal the presence of a gas in the atmosphere of these candidates, will not be without ambiguity. Oxygen is not synonymous with life. A good dose of interpretation will be essential to affirm that extraterrestrial microbes are involved.
It will be “very controversial” when the first scientists say that life has been found elsewhere, warns Mr. Doyon. Only when the same pattern has been spotted on several Earth-like exoplanets — which probably won’t happen with the James-Webb telescope, in operation since last year, but rather with its successors — will the community be able to start untying his tongue, he says.
But, in fact, 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 conception, ill-defined and unfairly limited to life as we know it, articulated around carbon, water and oxygen.
“Increase solar radiation 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 to look at those signatures [l’oxygène et le méthane, par exemple]. We can start there for logistical reasons, but we will also have to look for other complex behaviors. »
Everything that is alive evolves. But is everything that evolves in response to environmental pressures alive? Not necessarily. Evolution through natural selection can exist outside the traditional framework of biology as we know it, says the philosopher Bouchard.
An example in a solar system near you: in the atmosphere of Venus, current instruments reveal the presence “of a chemistry that we do not understand”, underlines the astrophysicist Étienne Artigau, of the University of Montreal . The complex photochemical reactions taking place there may satisfy a permissive definition of life. Missions planned for the 2030s will see.
Another mission, Dragonfly, will visit Titan, an icy moon of Saturn, where it is also suspected that very complex chemical reactions take place. “If we see a molecule which splits in two”, and which thus replicates itself, in a certain way, “what do we put in one of the New York Times ? asks Mr. Artigau. Do we say that we have found life elsewhere than on Earth?
Also among the presenters was Carla Bautista, a doctoral student in biology at Laval University, who studies the adaptation of organisms to extreme conditions: salinity, radiation, acidity, temperature, pressure, etc. It is in these extraordinary environments that we imagine that life appears.
In his laboratory, Mr.me Bautista grows yeast under ultraviolet (UV) lights. Yeasts evolve at breakneck speed: in one month, you can see 100 generations succeed one another. The researcher thus tests the “limits” of the adaptation of these organisms. And by association, she hopes to pinpoint more general limits of life.
If astrophysicists find a good candidate planet, the young researcher could test her yeasts under UV radiation equivalent to that of this outer space world. “Of course, you can only test life as you know it,” she says. But at least, with these experiments, one can obtain useful information on the limits of adaptation to stressful conditions. »
Extraterrestrial life can hold its own: Quebec scientists are waiting for it.