Exobiology or life in the Universe

For a long time, Homo Sapiens was certain that he (and therefore Earth) was the centre of Universe. Up until the end of the 20th century, he felt it probable that the Sun was the only star surrounded by planets. We now know that the Sun is an average star, that Earth is an average planet, that there are far more planets than stars in the Galaxy ^? , and that many of them probably have a solid surface, a temperate climate and liquid water.

Another crucial aspect to be considered is that [the physical and chemical processes at work in the Universe are the same everywhere]->rub11]: All of the atoms in the Universe can be found in the Mendeleiev table of elements. All the exoplanets follow the laws of gravitation established for the planets in the Solar System by Newton and Einstein.

• Exobiology or the study of life in the Universe

Exobiology is a branch of biology which consists in seeking out extra-terrestrial life and studying the effects of an extra-terrestrial environment on living organisms. The main aim of exobiology is thus to better understand the processes which created life, its evolution and its distribution on Earth and elsewhere in the Universe.

Scientists from a wide range of scientific disciplines such as astronomy, planetology, organic chemistry, palaeontology, as well as sub-disciplines of biology such as ecology and molecular biology, are involved in this vast field of research.

Space technologies play an important role in exobiology, because space probes are able to collect extra-terrestrial samples, as was done by the Japanese Hayabusa 2 probe which returned fragments of asteroid ^? Itokawa to Earth in 2010, or NASA’s Mars rovers such as Perseverance, which has taken core samples that we hope to bring back to Earth with the Mars Sample Return mission around 2030, if it is not cancelled.

Space missions are also needed to understand the particularity of the extra-terrestrial environment, for example the presence of volcanos, which are sources of heat but also the existence of significant radiation which could be harmful to the development of life similar to that on Earth.

Exobiology also includes the study of how prebiotic molecules ^? form in the interstellar medium ^?  or the atmospheres of comets ^? or satellites ^? such as Titan. The detection of these molecules would indicate that the building blocks necessary for the appearance of biological life could therefore come from space, brought back by comets ^? that have impacted the Earth.       
Exobiology is also attempting to plot the diagram of the evolution of life on Earth to better understand the evolution of our ecosystem and its biosphere.

Exobiologists are also studying the evolution of potential habitats on terrestrial planets ^? such as Mars, in the light of climatic and geophysical changes, in order to detect the existence of past or present life.

Finally, exobiology also includes the search for life in our Galaxy ^? , using three strategies:

• The search for life in our Solar System by means of space missions, including rovers on Mars, which probably had a vast surface ocean 4 billion years ago, the Dragonfly mission to Titan, and missions to satellites ^? that have an ocean of liquid water beneath their icy crusts, such as Enceladus and Europa, which are the targets of NASA’s Europa Clipper mission, launched in 2024, and the European JUICE mission, launched in 2023.

• The search for biological signals in the atmospheres of planets around other stars (exoplanets) using ground telescopes or the future large space telescopes, such as the intriguing presence of dimethyl sulphide in the atmosphere of the exoplanet K2-18b discovered by the JWST in 2025.

• The search for technological signals from advanced civilisations attempting to communicate with us or with themselves. The SETI project started barely 60 years ago and has grown with the arrival of new partners and new strategies, for example including the detection of laser signals.

The discovery and study of the evolution of an extra-terrestrial life could no doubt help with our understanding of life on Earth, its ecosystem and the processes which regulate it.

• The search for Earth twins

Planets with the mass of Earth have already been discovered in the habitable zone (HZ) around their star. But so far, these searches have only been possible around cold stars, where the HZ is close to the star and the planet’s orbital period ^? is thus short enough to be detectable. Planets with terrestrial mass and an orbital period ^? of one year are still inaccessible.

• Other civilisations in the Universe?

In answer to the question "Are there other intelligent / technologically advanced civilisations in the Universe?", One could respond that there are countless stars, even more planets, and that if life and intelligence (technology) appeared here, it must have happened elsewhere as well, perhaps even in many places. But if life were so common, why have we detected no signs of it (Fermi paradox)?

On the other hand, life on Earth could have benefited from a rare combination of favourable events. One approach is to break this question down into “simpler” factors, using the Drake equation which breaks down the calculation of the number of communicating civilisations in the Galaxy ^? into simpler terms, such as the number of stars and the number of habitable planets per star. While we have an estimate of the value of the first terms, we do not know, for example, the probability of life on a habitable planet.

• To find out more on habitability
• Quentin Kral’s book "Les astronomes à la recherche de vie extraterrestre", Ellipses, 2026, explores all aspects of the subject.