For the first time, NASA’s James Webb Space Telescope has directly captured images of carbon dioxide in planets beyond our Solar System. The findings, which focus on a famously key target for astronomers—HR 8799—located about 130 light-years away, shed new light on how the system’s four giant planets formed and suggest they may have grown similarly to Jupiter and Saturn.
“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,” said 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, this is an exciting conclusion.”
Greenhouse Gases Outside the Solar System
Exoplanets—planets that exist outside our solar system—are typically extremely challenging to observe. From Earth, a distant planet is often lost in the brilliant glow of its host star, much like trying to spot a candle flame beside a headlight. Webb’s suite of high-tech coronagraphs helps block that overwhelming starlight, making it possible to see these faint worlds and measure the makeup of their atmospheres more clearly than ever.
This achievement was made possible by these coronagraphs, revealing otherwise hidden worlds. Moreover, James Webb could identify infrared light in wavelengths that reveal specific gases and other atmospheric details.
HR 8799 is a relatively young system, only about 30 million years old. For comparison, our Solar System is 4.6 billion years old. It hosts four known giant planets that still glow brightly with the heat of their formation. Over the years, these planets have given scientists important clues about the birth of planetary systems. The new insights from Webb have now revealed an even more detailed picture, directly showing carbon dioxide signatures in their atmospheres.
A Glimpse at Planetary Origins
Planets can form in two broad ways. One is by “core accretion,” where solid materials collide and merge into a dense core that later collects a thick gas atmosphere. The other is “gravitational collapse,” where a large cloud of gas around a young star quickly contracts and forms a planet-like object. The latter is how our Solar System’s gas giants were thought to have formed, though on a grander scale.
The new Webb data strongly suggest that the HR 8799 planets developed much like Jupiter and Saturn. These young giant planets, brimming with heavier elements, fit neatly into the core-accretion model. Because they resemble the familiar gas giants of our own Solar System, researchers hope that learning how they shaped up will refine our understanding of how planets like Earth ultimately get a chance to form and survive.
“We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach,” said Laurent Pueyo of the Space Telescope Science Institute. “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.”
“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.”
The observations also revealed the first-ever detection of the innermost planet, HR 8799 e, and 51 Eridani b, showcasing Webb’s sensitivity to faint planets close to bright stars.
Ultimately, researchers aim to survey many more exoplanets with Webb’s coronagraphs, comparing the strength of carbon dioxide or other gases across different systems. Such comparisons will reveal just how similar or different distant solar systems may be from our own.
“We want to take pictures of other solar systems and see how they’re similar or different compared to ours,” Balmer said. “From there, we can try to get a sense of how unusual or how normal our solar system really is—or how normal.”
The study was published in The Astronomical Journal and spearheaded by a team of astronomers from Johns Hopkins University, the Space Telescope Science Institute, NASA’s Jet Propulsion Laboratory, among other institutions.
