Webb Directly Images Multiple Giant Exoplanets around Two Young Stars

Astronomers using the Near-Infrared Camera (NIRCam) onboard the NASA/ESA/CSA James Webb Space Telescope have captured coronagraphic images of the HR 8799 and 51 Eridani planetary systems. These observations have revealed the four known gas-giant planets encircling HR 8799 and one planet around 51 Eridani. They have also revealed that all HR 8799 planets are rich in carbon dioxide.

HR 8799 is a 30-million-year-old star located approximately 129 light-years away in the constellation of Pegasus.

It hosts a massive debris disk and four super-Jupiters: HR 8799b, c, d, and e.

Unlike most exoplanet discoveries, which are inferred from analysis of data, these planets are directly visible through ground-based telescopes.

“By spotting strong carbon dioxide features, we have shown there is a sizable fraction of heavier elements, like carbon, oxygen, and iron, in these planets’ atmospheres,” said Johns Hopkins University astronomer William Balmer.

“Given what we know about the star they orbit, that likely indicates they formed via core accretion, which is an exciting conclusion for planets that we can directly see.”

Still hot from their tumultuous formation, the planets within HR 8799 emit large amounts of infrared light that give scientists valuable data on how they formed.

Giant planets can take shape in two ways: by slowly building solid cores with heavier elements that attract gas, just like the giants in our Solar System, or when particles of gas rapidly coalesce into massive objects from a young star’s cooling disk, which is made mostly of the same kind of material as the star.

The first process is called core accretion, and the second is called disk instability.

Knowing which formation model is more common can give scientists clues to distinguish between the types of planets they find in other systems.

“Our hope with this kind of research is to understand our own Solar System, life, and ourselves in the comparison to other exoplanetary systems, so we can contextualize our existence,” Dr. 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.”

51 Eridani is located approximately 97 light-years from Earth in the constellation of Eridanus.

Otherwise known as 51 Eri, c Eridani or HD 29391, the star is only 20 million years old, a mere infant by astronomy standards.

It hosts one massive planet, 51 Eridani b, that orbits the star at a distance of about 13 AU (astronomical units) — equivalent to being between Saturn and Uranus in our Solar System.

The images of HR 8799 and 51 Eridani were made possible by Webb’s NIRCam coronagraph, which blocks light from bright stars to reveal otherwise hidden worlds.

This technology allowed the astronomers to look for infrared light emitted by the planets in wavelengths that are absorbed by specific gases.

They found that the four HR 8799 planets contain more heavy elements than previously thought.

“We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach” said Dr. Laurent Pueyo, an astronomer at the Space Telescope Science Institute.

“How common is this for planets we can directly image? We don’t know yet, but we’re proposing more Webb observations to answer that question.”

“We knew Webb could measure colors of the outer planets in directly imaged systems,” added Dr. Rémi Soummer, also from the Space Telescope Science Institute.

“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 findings were published in the Astronomical Journal.

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William O. Balmer et al. 2025. JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO₂ in the HR 8799 and 51 Eri Exoplanets’ Atmospheres. AJ 169, 209; doi: 10.3847/1538-3881/adb1c6