The search for planets outside our Solar System is accompanied by an ultimate goal in astronomy, namely, the discovery of a biosignature in an exoplanet. If the detection and characterization of exoplanets attract so many researchers, it is because at the end of this quest lies one of the ultimate goals of astronomy, the answer to the millennial question – “Is there any extraterrestrial life in the Universe?”
“It would be the end of the end, the Holy Grail”, summarizes Pierre-Olivier Lagage, an astrophysicist at the CEA and co-responsible for the MIRI instrument, one of the cameras of the future James Webb Space Telescope (JWST).
This telescope will have the task of analyzing the atmosphere of some exoplanets. The method consists in waiting for the planet to pass in front of its star and, at that precise moment, the gases that make up the exoplanet’s atmosphere absorb some of the light emitted by the star. The spectrum of this will then have some gaps betraying the molecules present in the exoplanet atmosphere.
In this spectrum examination, the researchers hope to read the biosignature, the mark of molecules indicating extraterrestrial life
Based on the example of the Earth where photosynthesis is breathing carbon dioxide into the air, astronomers have long dreamed that it would be enough to detect this molecule or traces of ozone on exoplanets.
However, nature could be tricky and abiotic processes, which occur without the presence of life, can intervene. For example, the UV light can break the water molecules on an exoplanet and the astronomer will detect oxygen but that wouldn’t mean there is any intelligent extraterrestrial life out there.
Recently, more and more experts agreed that finding oxygen or ozone in an exoplanetary atmosphere will not be a sufficient biosignature to confirm the existence of extraterrestrial life. It will be necessary to find certain molecules, found in certain proportions in the atmosphere of an exoplanet, which only then will be the sign of a chemistry impossible to explain without biology.