New James Webb Space Telescope (JWST) images show the first carbon dioxide-containing planet discovered outside of Earth’s solar system, displaying the telescope’s ground breaking research capabilities.
One hundred thirty thousand lightyears from Earth, the multiplanet system HR 8799 has been a primary target for astronomers studying planet formation. The new research confirms JWST’s ability to measure an exoplanet’s atmospheric chemistry and suggests the four planets formed similarly to Jupiter and Saturn, coalescing around a solid core.
Viewing a Young Solar System
At only 30 million years old, HR 8799 is relatively young compared to Earth’s 4.6 billion-year-old solar system. Due to their recent violent formation, the still-hot planets emitted great quantities of infrared light, providing scientists with important star formation data.
Although scientists have identified two ways giant planets form, they haven’t determined which is more prevalent in the universe. One method is to slowly accrete solid cores, like in our solar system, while the other is to collapse from a star’s cooling disc quickly. By identifying the most common method, scientists can better understand extrasolar bodies.
“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,” said project lead, William Balmer of Johns Hopkins University. “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 Exoplanet Challenge
Astronomers have directly imaged only a few exoplanets because they are much dimmer than stars, and difficult to discern at such great distances from Earth. JWST’s unique capabilities allow the platform to capture specific wavelengths to answer lingering astronomical questions. One of those is distinguishing between distant brown dwarfs, starlike objects that fail to accumulate enough mass for nuclear fusion ignition, and true giant planets.
James Webb Space Telescope
The clearest look in the infrared of HR 8799. Colors are applied to filters from Webb’s NIRCam (Near-Infrared Camera). CREDIT: NASA, ESA, CSA, STSCI, W. BALMER (JHU), L. PUEYO (STSCI), M. PERRIN (STSCI)
“We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach,” said Laurent Pueyo, an astronomer at the Space Telescope Science Institute who co-led the work.
“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,” Pueyo added.
James Webb Space Telescope Coronagraphs
The JWST produces images called “coronagraphs,” created by blocking light from bright stars, like in an eclipse, to make dimmer bodies more visible against space’s black background. The team utilized that technique to capture atmospheric details such as specific gas compositions.
Their target was the 3-5 micrometer wavelength range, within which they discovered elements heavier than expected, suggesting slow accretion formation. The imaging technique’s sensitivity was so great that it was the first to detect HR 8799, the system’s innermost planet.
“This is what scientists have been doing for transiting planets or isolated brown dwarfs since the launch of JWST,” Pueyo said.
critical thinking
“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,” said Rémi Soummer, previous leader of JWST coronagraph operations.
James Webb Space Telescope Continues On
While this is the first direct evidence of a carbon dioxide-containing exoplanet, JWST found indirect evidence of CO₂ in exoplanet WASP-39b in 2022. Astronomers collected that evidence by monitoring how starlight changed when filtered through the atmosphere as WASP-39b moved in front of its star. The team plans to observe further gas giants for comparison to theoretical models, improving understanding of the wider cosmos, as well as our own solar system.
“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 paper “JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO2 in the HR 8799 and 51 Eri Exoplanets’ Atmospheres” appeared on March 17, 2025 in The Astrophysical Journal.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted atryan@thedebrief.org, and follow him on Twitter@mdntwvlf.