The James Webb Space Telescope (JWST), a cooperation between NASA, the European Space Agency, and the Canadian Space Agency, has caught definitive evidence of carbon dioxide in the atmosphere of a gas giant planet circling a Sun-like star 700 light years away.

The result, which has been accepted for publication in Nature, provides important insights into exoplanet composition and formation and is indicative of Webb’s ability to detect and measure carbon dioxide in the thinner atmospheres of smaller rocky planets. And furthermore, a better understanding of such exoplanets could lead to the discovery of worlds that could harbor extraterrestrial life.

The team that made the discovery was granted time on the telescope through the Early Science Publication Program, which was selected to collect some of Webb’s first data after its science operations began in late June Led by Natalie Batala of the University of California, Santa Cruz, the team includes astronomers from around the world, including Björn Benneke of the Université de Montréal, who is also a member of the Institute for Exoplanet Research (iREx).

The target of the monitoring program, WASP-39 b, is a hot gas giant with a mass roughly a quarter that of Jupiter (about the same as Saturn) and a diameter 1.3 times that of Jupiter. Its exceptional puffiness is due in part to the high temperature (about 900°C). 

Unlike the cooler, more compact gas giants in our Solar System, WASP-39 b orbits very close to its star – only about one-eighth the distance between the Sun and Mercury – completing one orbit in just over four Earth days . 

The discovery of the planet, reported in 2011, was based on ground-based detections of the subtle, periodic dimming of light from its host star as the planet transits, or passes in front of, the star.

During transit, some of the starlight is completely blocked by the planet (causing total dimming) and some passes through the planet’s atmosphere. Because different gases absorb different combinations of colors, researchers can analyze small differences in the brightness of transmitted light across a spectrum of wavelengths to determine exactly what the atmosphere is made of.

With its combination of inflated atmosphere and frequent transits, WASP-39 b is an ideal target for transmission spectroscopy. The team used Webb’s (NIRSpec) to make this discovery.

First clear detection of CO2A transmission spectrum of the hot-gas exoplanet WASP-39 b, imaged by Webb’s (NIRSpec) on July 10, 2022, reveals the first definitive evidence of carbon dioxide on a planet outside the Solar System. 

What the discovery team saw was extremely impressive. A significant signal—an absorption feature—was detected at wavelengths between 4.1 and 4.6 microns in the infrared range. This is the first clear, detailed and indisputable evidence of carbon dioxide ever found on a planet outside the solar system.

“I was absolutely blown away,” said Benecke, a UdeM physics professor and member of the Transiting Exoplanet Team who worked on the concept of the observing program and the analysis of the NIRSpec data with UdeM graduate students Louis-Philippe Coulomb, Caroline Piolet, Michael Radica and Pierre-Alexis Roy and postdoctoral fellow Jake Taylor.

“We were analysing the data here in Montreal and we saw this huge carbon dioxide signature: 26 times stronger than any noise in the data. Before JWST, we often dug into the noise, but here we had a perfectly solid signature. It’s like seeing something clearly with your own eyes.”

Björn Benneke, a professor at Université de Montréal and iREx, is a key member of the team that discovered the first definitive signature of carbon dioxide in an exoplanet atmosphere.

No observatory has ever measured such subtle differences in the brightness of so many individual infrared colors in the exoplanet transmission spectrum before. 

Access to this part of the spectrum, from 3 to 5.5 microns, is critical for measuring abundant gases such as water and methane, as well as carbon dioxide, that are believed to exist in many different types of exoplanets.

“Finding such a clear carbon dioxide signal on WASP-39 b bodes well for the discovery of atmospheres on smaller Earth-sized planets,” said Batala, the program’s principal investigator.

“On Earth,” Beneke added, “carbon dioxide plays such an important role in our climate, and we’re used to seeing its spectroscopic signatures here. Now we see that signature on a distant world. It really drives home the message that these exoplanets are real worlds: as real as Earth and the planets in our solar system.”

The James Webb Space Telescope is the world’s leading space science observatory. Webb will solve mysteries in our solar system, look beyond distant worlds around other stars, and explore the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners ESA (European Space Agency) and the Canadian Space Agency.

Reference(s): NASA