Indisputable signs of the presence of CO2 on an exoplanet

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Indisputable signs of the presence of CO2 on an exoplanet

Artistic representation showing what the exoplanet WASP-39 b could look like, according to current knowledge of the planet.

Clear and precise evidence of the presence of carbon dioxide (CO2) in the atmosphere of a gas giant exoplanet has been detected by an international team of scientists, from data collected using the James Webb Telescope .

This is the first detailed and indisputable evidence for the presence of carbon dioxide ever found on a planet outside the solar system.

Professor Björn Benneke and a team of doctoral students from the University of Montreal and the Institute for Research on Exoplanets (iREx) participated in this work led by astronomer Natalie Batalha, from the #x27;University of California, Santa Cruz, which will be published in the journal Nature.

Astrophysicists used James Webb's Near Infrared Spectrograph (NIRSpec) to observe the planet WASP-39b. And what they discovered is clear: there is indeed CO2 in its atmosphere.

The data analyzed in Montreal detected a huge signature of carbon dioxide around the planet, no less than 26 times stronger than any noise in the data, notes Prof. Benneke.

Noise can be compared to inaccuracies in the field of vision. To illustrate this, the professor compares the arrival of James Webb to the transition from analog TV to 4k TV.

“It was a very, very special moment for me. As a scientist, I'm always very skeptical, but in this case, it was like seeing something with my own eyes. »

— Björn Benneke, University of Montreal and iREx

Professor Benneke says this study shows the space telescope's ability to detect and measure CO2 in very hot atmospheres. thin, even those of small and rocky planets like the Earth.

It really is a new era in astronomy that is opening up, enthuses the astrophysicist.

This detection was achieved thanks to five hours of use of the NIRSpec instrument, which the international team obtained as part of the Early Release Science program. This one started at the end of June; its first results were announced in July.

Artist's rendering of the James Webb Space Telescope.

The target of the observing program, the planet WASP-39 b, orbits a Sun-like star located 700 light-years from Earth.

The mass of this hot gas giant is about a quarter of that of Jupiter, and its diameter is 1.3 times larger.< /p>

Unlike the cooler, more compact gas giants in our solar system, WASP-39 b orbits very close to its star, barely one-eighth the distance between the Sun and Mercury. In addition, it completes the tour in just over four Earth days.

Its atmosphere seems inflated compared to other planets, a phenomenon probably linked in part to its temperature high around 900°C.

The planet was detected in 2011 using the transit technique which shows a subtle, periodic dimming of a star's light as the planet transits, or passes, in front of the star.

Because of its swollen atmosphere and its frequent transits, WASP-39 b was therefore a perfect target for carrying out transmission spectroscopy, which also makes it possible to specify the composition of a planet's atmosphere thanks to transit. Some light from the star passes through the planet's atmosphere. This light is filtered by the atmosphere and allows us to measure its composition, explains Prof. Benneke.

“Gases absorb different color combinations, allowing us to analyze small differences in brightness across various wavelengths to determine exactly what the planet's atmosphere is made of. »

— Björn Benneke, University of Montreal and iREx

Detection of the telltale signal, an absorption line, was performed at wavelengths between 4.1 and 4.6 microns in the infrared.

A transmission spectrum of the hot gas giant exoplanet WASP-39b captured by 'James-Webb's' near-infrared spectrograph (NIRSpec) on July 10, 2022 reveals the first definitive evidence for the presence of carbon dioxide on a planet outside the solar system.

No telescope or observatory has ever before measured such subtle differences in the brightness of so many individual infrared colors in an exoplanet's transmission spectrum. Access to this part of the spectrum (3 to 5.5 microns) is crucial in determining the abundance of gases like water and methane, as well as CO2, which could exist in many different types of exoplanets.

Water vapor has also been detected in the atmosphere of the exoplanet.

On our planet, carbon dioxide plays an extremely important role, since it influences the climate, a climate that allows the presence of life. It could play a similar role in the emergence of life elsewhere.

As a molecule, it is very important. For example, Venus is a very hot planet due to the presence of a lot of CO2 which, due to the greenhouse effect, heats the surface. We are beginning to study distant planets like WASP-39 b in the same way as those in the solar system, underlines the professor.

“The fact that CO2 exists gives us an idea of ​​the formation of the planet. The abundance of CO2 in its atmosphere is similar to that of Saturn, but not like Jupiter. »

— Björn Benneke, University of Montreal and iREx

The teams that analyzed the planet's spectrum also detected the presence of something there that they cannot explain and that does not has never been detected elsewhere. There is a mysterious molecule in its spectrum, something we are still trying to understand, Prof. Benneke wonders.

Predictive models of planetary chemistry are currently being modified to try to interpret this observation.

This is a great surprise for all researchers. There is probably something about the high-temperature chemistry of certain elements that remains to be understood, argues the professor.

Analyses carried out in the coming months should help to explain this mysterious chemical signature.

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