Webb Spies First Direct Images of CO2 Outside Solar System

For the first time, scientists have directly imaged carbon dioxide in the atmospheres of planets outside our solar system, offering unprecedented insight into how giant worlds form. Using the James Webb Space Telescope (JWST), researchers captured these groundbreaking observations of planets in a system located 130 light-years from Earth.

The discovery, published yesterday in The Astrophysical Journal, strengthens the evidence that massive planets in distant star systems likely formed through the same process that created Jupiter and Saturn in our own cosmic neighborhood.

Researchers focused their observations on HR 8799, a star system containing four giant planets that has fascinated astronomers since its discovery in 2008. By analyzing the specific wavelengths of infrared light coming from these worlds, the team confirmed the presence of carbon dioxide and other heavy elements in their atmospheres.

“By spotting these strong carbon dioxide features, we have shown there is a sizable fraction of heavier elements, such as carbon, oxygen, and iron, in these planets’ atmospheres,” explained William Balmer, a Johns Hopkins University astrophysicist who led the research. “Given what we know about the star they orbit, that likely indicates they formed via core accretion, which for planets that we can directly see is an exciting conclusion.”

Core accretion—the gradual building of solid planetary cores that eventually attract gas—is one of two major theories for how giant planets form. The alternative theory suggests they could form rapidly through the collapse of material directly from a young star’s cooling disk. The new findings help scientists distinguish between these competing models.

The Webb telescope’s exceptional capabilities allowed the team to directly observe these distant worlds, a feat that remains extremely challenging. Most exoplanets are too faint compared to their host stars to be directly imaged. Using specialized instruments called coronagraphs, which block the overwhelming light from stars much like what happens during a solar eclipse, Webb was able to reveal what would otherwise remain hidden.

“Our hope with this kind of research is to understand our own solar system, life, and ourselves in comparison to other exoplanetary systems, so we can contextualize our existence,” Balmer said. “We want to take pictures of other solar systems and see how they’re similar or different when compared to ours. From there, we can try to get a sense of how weird our solar system really is—or how normal.”

The observations also included another planetary system called 51 Eridani, which lies 96 light-years away. The team was able to target specific wavelengths of light that reveal information about atmospheric composition using Webb’s specialized instruments.

Laurent Pueyo, an astronomer at the Space Telescope Science Institute who co-led the work, noted the broader significance of the findings. “We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach,” he said. “How common is this for long period planets we can directly image? We don’t know yet, but we’re proposing more Webb observations, inspired by our carbon dioxide diagnostics, to answer that question.”

This isn’t the first time Webb has detected carbon dioxide in an exoplanet’s atmosphere. In 2022, the telescope indirectly detected carbon dioxide in a planet called WASP-39 b by measuring how the planet’s atmosphere altered starlight as it passed in front of its star. The new findings represent the first direct imaging of carbon dioxide in exoplanet atmospheres.

“This is what scientists have been doing for transiting planets or isolated brown dwarfs since the launch of JWST,” Pueyo explained, distinguishing between different observation techniques.

Rémi Soummer, who directs the Optics Laboratory at the Space Telescope Science Institute and previously led Webb’s coronagraph operations, added: “We knew JWST could measure colors of the outer planets in directly imaged systems. We have been waiting for 10 years to confirm that our finely tuned operations of the telescope would also allow us to access the inner planets. Now the results are in, and we can do interesting science with it.”

The implications extend beyond simply understanding how these specific planets formed. As Balmer explained, giant planets can significantly influence the development of smaller, potentially habitable worlds like our own.

“These giant planets have pretty big implications,” Balmer said. “If you have these huge planets acting like bowling balls running through your solar system, they can either really disrupt, protect, or do a little bit of both to planets like ours, so understanding more about their formation is a crucial step to understanding the formation, survival, and habitability of Earth-like planets in the future.”

The research team plans to expand their analysis to more giant planets, comparing their composition to theoretical models. As Webb continues to reveal the chemical makeup of distant worlds, scientists are steadily piecing together a more comprehensive picture of how planetary systems—including our own—come to be.