exoplanet

Published on : 26/08/2022 – 17:32

Humanity had so far never detected any outside our solar system. At least not in a certain way. Observations from the James Webb Space Super Telescope (JWST) brought, Thursday, August 25, the definitive proof. For the first time, carbon dioxide has been detected in the atmosphere of an exoplanet (i.e. outside the solar system).

The giant eye of the brand new telescope, launched on December 25, 2021, turned to the near vicinity of our galaxy to search for traces of CO². He found some around the planet WASP-39b which is “only” some 700 light years from Earth. It’s only a few stardust blocks away from home compared to, say, the galaxy CEERS-93316 that the James Webb instrument detected 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 have confirmation that the JWST actually allows us to identify this important molecule in the atmosphere of an exoplanet,” says Hannah Wakeford, an astrophysicist at the University of Bristol, member of the international research team who wrote up the findings from the WASP-39b sighting, which will be published in the journal Nature on August 29.

The Hubble telescope, predecessor of the James Webb, had already made it possible to observe in 2008 what looked like CO² in the atmosphere of an exoplanet, but “it was only a single clue 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 carried out 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 did not have the tools to detect with certainty the presence of CO²“, explains Hannah Wakeford. The JWST is, in fact, the first space observation instrument to be able to detect certain wave frequencies in the infrared. And it is precisely in this zone that carbon dioxide blocks light. “Each molecule will absorb light in a different way, which gives it a particular signature on the readings of the telescope”, details Jérémy Leconte.

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

With 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 of the presence of life. This is because on our planet, CO emissions² in the atmosphere generally come from living organisms. They can be produced during the decomposition of organic matter or come from animal respiration.

But that the hunters of extra-terrestrial arrange their net with small green men. “The presence of CO² in the atmosphere of a planet is, in fact, a very poor indicator of the presence of life”, affirms Hannah Wakeford. The atmosphere of Venus, for example, is saturated with carbon dioxide whereas it is about a planet 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 the 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”, underlines Jérémy The tale.

The holy grail for space archaeologists

The detection of CO2 is nonetheless essential for astrophysicists because “it is a very good indicator for understanding the history of a planet”, notes Hannah Wakeford. The presence of this molecule provides, first of all, “a serious indication that the planet has an atmosphere”, which is far from being the case for all the planets of the Universe (in our own solar system, Mercury has no atmosphere). And the atmosphere keeps the chemical traces of all the history of the planet.

Thus, the data transmitted by JWST on the atmosphere of WASP-39b – and in particular the concentration of CO² – already allow us to make a first observation: this planet comes from elsewhere. Indeed, 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 amassed 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 while moving from its place of formation to its current position”. Now remains to know where it comes from.

These first observations by the 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 to find molecules like CO²“, enthuses Jérémy Leconte. In this respect, this device is indeed, 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 sites on tens and hundreds of exoplanets to understand their formations and, ultimately, to know how unique our Earth is in the Universe.