Will we end up finding life elsewhere than on Earth?

Imagine a picture of our galaxy, the Milky Way. Inside the spiral, billions of stars, planets orbiting these stars, and between them a vast void. In one corner there is a small shining grain of sand: it is us, the Earth and its eight billion inhabitants, its biodiversity, its billions of animals, plants, fungi and bacteria. In this picture there may be a life other than ours.

Find all episodes of our summer series dedicated to extraterrestrial life

This is what thousands of scientists have followed for years, aided by technological advances and the expansion of their knowledge as new discoveries are made. We take you with us to follow this search for life and traces of life, during a journey of several thousand light years.

What exactly are we looking for?

Before departure, some travel instructions are in order. What exactly are we looking for? Life or traces of life as we could find them on Earth: we start from the postulate that the entire universe is composed of the same chemical elements, therefore life will also consist of the same starting stones. To seek life one must try to understand what life is. Our only reference is on Earth, so we’re looking for Earth-like life on an Earth-like planet.​, explains Lucie Leboulleux, researcher at the Grenoble Institute of Planetology and Astrophysics (IPAG).

“We are not observing green men, but molecules”adds astrophysicist Anthony Boccaletti, CNRS research director and specialist in exoplanets.

We therefore forget the aliens built into our image by movies or literature, although the hope of one day finding an intelligent life form remains with some scientists.

Exobiologist Nathalie Cabrol, director of the Carl Sagan Research Center of the SETI Institute in the United States, declared it especially France Inter on 24 September 2021 “Statistically, when you look at the distribution of life on Earth, most life in the universe is probably microscopic and simple. But the more microscopic and simple life we ​​find, the more likely we are to find technologically advanced life. Look at the Earth. The life there is 95% microbial, and there is one species that is able to escape from its planet to seek life elsewhere”.

Finally, to find places likely to harbor life, scientists use a much-discussed concept today: the habitable zone. “The habitable zone is the presence of liquid water, at a certain distance from the star, at a certain pressure. It is criticized in terms of communication, because habitable does not mean inhabited , specifies Lucie Leboulleux. And that closes the door to many other forms of life. » In the solar system, the habitable zone includes only Earth, and yet scientists today have hopes of finding life outside this zone. Around Jupiter or Saturn for example.

The hunt for extraterrestrial life begins… on Earth

Let’s start our journey in a not so distant place: Lake Licancabur, on the border between Bolivia and Chile. Altitude: 5,900 meters. It is one of the most inhospitable places on Earth: located at a very high altitude, on top of a volcano, it receives a lot of UV radiation…

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