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The first observations of an exoplanet’s atmosphere by the James Webb Space Telescope, released Thursday, revealed the presence of CO2 around WASP-39b. This first detection of this chemical compound outside our solar system confirms that the telescope will allow us to understand the formation of the most distant planets.
Until now, humanity had never detected any outside our solar system. At least not in a certain way. Observations from the James Webb Super Space Telescope (JWST) brought, on Thursday, August 25, the definitive proof. For the first time, carbon dioxide has been detected in the atmosphere of an exoplanet (ie outside the solar system).
The giant eye of the new telescope, launched on December 25, 2021, went to the immediate vicinity of our galaxy to search for traces of CO.two. He found some around the planet WASP-39b, which is “only” about 700 light-years from Earth. It’s just a few blocks of stardust away from us compared, for example, to the CEERS-93316 galaxy that the James Webb instrument detected in early August more than 13 billion light-years from Earth.
The first tool capable of “seeing” COtwo in the air
“We suspected that we would end up finding COtwobut it’s always nice to have confirmation that JWST really allows us to identify this important molecule in an exoplanet’s atmosphere,” says Hannah Wakeford, an astrophysicist at the University of Bristol, a member of the international research team that wrote up the findings of the sighting. WASP-39b, to be published in the journal Nature on August 29.
The Hubble telescope, predecessor of the James Webb, had already observed in 2008 what seemed like COtwo in the atmosphere of an exoplanet, but “it was just a hint suggesting the presence of carbon dioxide,” says Jérémy Leconte, an astrophysicist at the University of Bordeaux who was also a member of the team that made the WASP-39b observations. “There, when we saw the readings broadcast by JWST, there was no possible doubt,” he adds.
“Until now, we just didn’t have the tools to detect with certainty the presence of COtwo“explains Hannah Wakeford. The JWST is, in fact, the first space observation instrument capable of detecting certain wave frequencies in the infrared. And it is precisely in this area where carbon dioxide blocks light. “Each molecule will absorb the light in a different way, which gives it a particular signature in the telescope’s readings”, details Jérémy Leconte.
And it’s not just the first time that COtwo detected in the atmosphere of an exoplanet. It is also the first confirmation of the presence of this molecule in a planet of the WASP-39b type, that is, a gas giant similar to Jupiter, all the galaxies together… including our solar system. In fact, he has never been able to prove that there were any on Jupiter or Saturn.
COtwoa “poor indicator of the presence of life in space”
Seen from Earth, this discovery of carbon dioxide in WASP-39b could easily give rise to fantasies about the presence of life. This is because on our planet, CO emissionstwo in the atmosphere usually come from living organisms. They can be produced during the decomposition of organic matter or come from animal respiration.
But that alien hunters cast their net with little green men. “The presence of COtwo in a planet’s atmosphere is, in fact, a very poor indicator of the presence of life”, says Hannah Wakeford. The atmosphere of Venus, for example, is saturated with carbon dioxide when it is a particularly hostile planet to all forms of life, if only because of the extremely high surface temperature (over 400°C).
WASP-39b also experiences extreme temperatures, approaching 900°C, in its atmosphere. Where does CO come from?two ? “C’est le résultat d’une réaction chemique lorsqu’on mélange du carbone, de l’hydrogène et de l’hélium – autant d’éléments présents dans l’atmosphère de cette exoplanète – à de très fortes températures”, souligne Jérémy Count.
The holy grail for space archaeologists
Still, detecting CO2 is essential for astrophysicists because “it’s a very good pointer to understanding the history of a planet,” says Hannah Wakeford. The presence of this molecule provides, first of all, “a serious indication that the planet has an atmosphere”, which is far from the case for all planets in the Universe (in our own solar system, Mercury has no atmosphere). And the atmosphere holds the chemical traces of the entire history of the planet.
Thus, the data transmitted by JWST about the atmosphere of WASP-39b – and in particular the concentration of COtwo – Let us make a first observation: this planet comes from elsewhere. In fact, it is currently very close to its star – quite similar to our sun, according to the experts interviewed – and “it is physically impossible that by staying there it has accumulated so much COtwo and oxygen in its atmosphere”, assures Hannah Wakeford. For her, there are not 1001 possibilities: WASP-39b has “recovered elements of COtwo and oxygen as it moves from its place of formation to its current position.” Now it remains to be seen where it comes from.
These first JWST observations of the atmosphere of an exoplanet have confirmed “that it is really possible to carry out this type of detection and find molecules such as COtwo“, enthuses Jérémy Leconte. In this sense, this device is, in fact, for Hannah Wakeford, the long-awaited Holy Grail of space archaeology. With a very “terracentric” approach, since the goal will be with JWST to multiply the sites .about tens and hundreds of exoplanets to understand their formations and, in short, to know how unique our Earth is in the Universe.
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