The discovery delighted the scientific community. NASA announced on Thursday August 25 that the James Webb Space Telescope had detected traces of CO2 in the atmosphere of WASP-39b, an exoplanet located 700 light years from Earth.
This one, massive (about a quarter of the mass of Jupiter), brings together the ideal criteria to leave room for observation. The James Webb telescope uses spectroscopy for this, ie the study of the spectra of electromagnetic radiation, emitted or absorbed by a substance. The term “spectrum” here corresponds to light, divided into several wavelengths. In the same way that sunlight can be broken down into the colors of a rainbow, but much more precisely.
In the field of astrophysics, this consists in capturing the variations in luminosity, when a planet passes in front of its star for example, in order to then analyze it. It is here that WASP-39b gathers the best conditions, by its size, but also by its proximity to its star, since it goes around it in four days.
A “one-of-a-kind” telescope
By studying the spectrum of an exoplanet, scientists can observe the unique composition of its atmosphere. Each molecule leaves behind a particular signature, “like an identity card”compares Anne-Marie Lagrange, director of research in astrophysics at the CNRS. “When we detect signatures at a specific place in a spectrum, this tells us the presence of an atom, or a molecule”she says.
Spectroscopy is the method used ” by all ” in this field of research, says Anne-Marie Lagrange, director of research in astrophysics at the CNRS. But the James Webb Telescope is here « unique in son genre », insists the researcher, mainly because of her position. This is indeed outside the Earth’s atmosphere and can work on wavelengths almost invisible from the ground.
Primary objective: to characterize the atmospheres studied
“James Webb is going to be extraordinary in characterizing the atmospheres of new planets. » emphasizes Anne-Marie Lagrange. This type of progress, often relegated to the background behind the unpublished images of Jupiter, is not “not an end, but above all a base, a first step”she rejoices.
If WASP-39b remains unsuitable for life, James Webb may on the other hand be led to observe other planets, much less massive, much less close, but more similar to our Earth.
For the CNRS researcher, demonstrating that we can access CO molecules2 will be very important to understand the history of the formation of the planets. “When it comes to looking for signs of life somewhere, it is also this method that should be used”she adds.
For this, detecting the presence of carbon dioxide will not be sufficient. “We will then look for the presence of many molecules, to have a complete vision of the composition of the atmosphere of a given planet”explains Anne-Marie Lagrange, who indicates that new programs will be released ” very soon “relating to planets much more distant.