With WASP-39b, the James Webb telescope is paving the way for the archaeologists of the universe

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The first observations of an exoplanet’s atmosphere by the James Webb Space Telescope, published 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 make it possible to understand the formation of the most distant planets.

Humanity had never before discovered anyone outside our solar system. At least not in a certain way. The observations by the James Webb Space Super Telescope (JWST) on Thursday, August 25, brought the final proof. For the first time, carbon dioxide has been detected in the atmosphere of an exoplanet (ie outside the solar system).

Launched on December 25, 2021, the giant eye of the brand new telescope turned to our nearby galaxy to search for traces of CO2. He found some around the planet WASP-39b, which is “only” about 700 light years from Earth. It is only a few blocks of stardust away from us compared to, for example, the CEERS-93316 galaxy, which the James Webb instrument discovered in early August more than 13 billion light years from Earth.

The first tool capable of “seeing” CO2 in the air

“We suspected that we would end up finding CO2but it’s always good to get confirmation that JWST is indeed allowing us to identify this important molecule in the atmosphere of an exoplanet,” says Hannah Wakeford, astrophysicist at the University of Bristol, a member of the international research team that wrote the WASP results -39b observation, which will be published in the journal Nature on August 29.

The Hubble telescope, the predecessor of James Webb, had already observed in 2008 what looked like CO2 in the atmosphere of an exoplanet, but “it was only a single trace that suggested the presence of carbon dioxide”, notes Jérémy Leconte, astrophysicist at the University of Bordeaux, who was also a member of the team that made the observations of WASP-39b. “There, when we saw the readings transmitted by JWST, there was no possible doubt,” he adds.

“Until now, we simply didn’t have the tools to reliably detect the presence of CO2“, explains Hannah Wakeford. JWST is actually the first space observation instrument capable of detecting certain wave frequencies in the infrared. And it is precisely in this zone that carbon dioxide blocks the light. “Each molecule will absorb light in a different way, which gives it a special signature on the readings of the telescope”, says Jérémy Leconte.

And it is not only the first time that CO2 detected in the atmosphere of an exoplanet. It is also the first confirmation of the presence of this molecule on a planet of the type WASP-39b, that is, a gas giant similar to Jupiter, all galaxies combined… including our solar system. It has never actually been able to prove that there was anyone on Jupiter or Saturn.

CO2a “poor indicator of the presence of life in space”

Seen from Earth, this discovery of carbon dioxide on WASP-39b could easily give rise to fantasies about the presence of life. This is because on our planet, CO emissions2 in the atmosphere generally comes from living organisms. They can be produced during the decomposition of organic matter or come from animal respiration.

But that the hunters of extraterrestrials arrange their nets with little green men. “The presence of CO2 in the atmosphere of a planet is actually a very poor indicator of the presence of life”, confirms Hannah Wakeford. The atmosphere of Venus, for example, is saturated with carbon dioxide, whereas it is about a planet that is particularly hostile to all forms of life. , if only because of the very high surface temperature (over 400°C).

WASP-39b also experiences extreme temperatures approaching 900°C in its atmosphere. Where does CO come from?2 ? “It is the result of a chemical reaction when carbon, hydrogen and helium are mixed – all elements present in the atmosphere of this exoplanet – at very high temperatures”, emphasizes Jérémy The speech.

The Holy Grail for space archaeologists

The detection of CO2 is nevertheless crucial for astrophysicists because “it is a very good indicator for understanding the history of a planet”, notes Hannah Wakeford. The presence of this molecule gives, 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 preserves the chemical traces of the planet’s entire history.

Thus transmitted data from JWST about the atmosphere of WASP-39b – and especially the concentration of CO2 – allow us already to 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 could have collected so much CO2 and oxygen in its atmosphere”, assures Hannah Wakeford. For her there are not 1001 possibilities: WASP-39b has “recovered elements of CO2 and oxygen as it moves from its place of formation to its present position”. Now we need to know where it comes from.

These first observations by JWST of the atmosphere of an exoplanet have made it possible to confirm “that it is really possible to carry out this kind of detection and find molecules like CO2“, enthused Jérémy Leconte. In this respect, this device is really, for Hannah Wakeford, the long-awaited holy grail of space archaeology. With a very “terra-centric” approach, since the goal will be with JWST to multiply the locations of tens and hundreds of exoplanets for to understand their formations and ultimately to know how unique our Earth is in the universe.

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