On March 21, 2022, NASA announced that the symbolic band of 5,000 officially identified exoplanets had just been crossed following the addition of 65 new specimens to the US Space Agency’s (NASA Exoplanet Archive) catalog. They form a bestiary of great variety. These objects include: small telluric planets similar to Earth, miniature versions of Neptune, “hot Jupiters” very close to their star, gas giants even more impressive than Jupiter’s star, or even “super-Earths” more massive than our planet. , but still would have a rocky surface… Not to mention objects orbiting a couple of stars or remaining near collapsed stellar corpses. “Each of them is a whole world, a whole new planet.Jesse Christiansen, the astrophysicist who runs this catalog, enthuses in a press release. And I’m in awe of all these planets because we don’t know anything about them yet..”
Giant planets that have no analogues in the solar system
The first detections of exoplanets were confirmed in 1992, that is, only thirty years ago. They revolved around a certain type of neutron star called a pulsar, which revolves around itself very quickly and emits intense radiation at a frequency of the order of a millisecond. Three years later, in 1995, Swiss astronomers Michel Mayor and Didier Quelo discovered the first exoplanet around a sun-like star. To do this, they relied on small backward movements caused by the rotation of the planet around the star. The planet in question was a “hot Jupiter”: a giant planet unparalleled in the solar system, very close to its star, and completing an orbit in just four days (compared to 12 years for our Jupiter).
An extremely successful method
As of 2009, another detection method called “transits” will prove to be extremely fruitful. It consists of recording tiny dips in luminosity (about 1%) as the planet passes in front of its star, a bit like an eclipse. The Kepler Space Telescope, operated by NASA between 2009 and 2018, has been able to identify over 2,700 exoplanets, the most objects listed to date. Other instruments have emerged to enhance this tracking, such as the Hubble Space Telescope, the European Southern Observatory’s HARPS spectrograph (High Precision Search for Planets at Radial Velocities), the American TESS Space Telescope (Exoplanet Transit Satellite) or, since 2019, the European CHEOPS satellite. (Characterising ExOPlanets Satellite). With great success. Because if 4,000 exoplanets were identified in the summer of 2019, it would take less than three years to add another 1,000.
The discovery of extraterrestrial life was only a matter of time
However, the quest has only just begun. Of the 5,005 objects counted to date, 98% are in our “near neighborhood,” just a few thousand light-years from our star. Thus, there are myriads of others to be discovered among the hundreds of billions of exoplanets that will inhabit our galaxy. Faced with such opportunities, such dizzying numbers,it is inevitable that we will find a form of life somewhere“, – says astronomer Alexander Volshchan, who with his team discovered the very first exoplanet in 1992.”The close relationship between the chemistry of life on Earth and the chemistry at work in the universe, together with the wide presence of organic molecules, suggests that the discovery of life itself is only a matter of time.“
Exoplanet atmospheres under scrutiny by JWST
It is expected that at the end of the decade, the next generation of ground and space telescopes, such as the US Nancy Grace Roman Space Telescope or the European ARIEL (Large Infrared Atmospheric Remote Sensing Survey of Exoplanets), may enable these crucial discoveries. In the meantime, all eyes are on the JWST (James Webb Space Telescope). Created by the American, European and Canadian space agencies, it is currently in the calibration phase at a distance of 1.5 million kilometers from Earth. Equipped with a primary mirror with a diameter of 6.5 meters, it is the largest and most powerful observation instrument ever sent into space. And from this summer, it will be able to scan the atmosphere of exoplanets – especially gas giants – with unsurpassed accuracy, in particular, looking for any biosignatures, such as, for example, ozone molecules.