Astronomers Uncover the Formation of 'Super Jupiters' Around a Remote Star
The planets in our solar system formed from a disk of material swirling around the Sun, with inner rocky planets growing from tiny grains to boulders and eventually full-grown planets. Outer gas and ice giants also accumulated cores of rocky material, attracting cooler gas and ice halos. But what about planets that are even larger and farther from their star than Jupiter? Could they form like stars through gravitational instability, or like planets via core accretion?
A team of researchers used spectral data from NASA's James Webb Space Telescope (JWST) to explore this question. They studied the HR 8799 star system, located 133 light-years away in the constellation Pegasus, which hosts four super Jupiters. Each of these planets has a mass five to ten times that of Jupiter and orbits at distances between 15 to 70 astronomical units, with the closest planet being 15 times farther from its star than Earth is from the Sun.
The findings, published in Nature Astronomy, reveal that the third planet, HR 8799 c, contains sulfur. This is significant because sulfur-containing molecules would be solid in a planet-forming disk, unlike carbon and oxygen-containing molecules. This discovery suggests that HR 8799 c formed through core accretion. The scientists believe sulfur is likely present in all three of the star's innermost planets, which are more enriched in heavy elements like carbon and oxygen, further supporting their planetary formation.
Jean-Baptiste Ruffio, a co-lead study author, highlights the importance of JWST's sensitivity in enabling detailed studies of these planets' atmospheres. "With its unprecedented sensitivity, JWST is enabling the most detailed study of the atmospheres of these planets, giving us clues to their formation pathways," Ruffio says. "With the detection of sulfur, we are able to infer that the HR 8799 planets likely formed in a similar way to Jupiter despite being five to 10 times more massive, which was unexpected."
Charles Beichman, another co-author, emphasizes the significance of this discovery in understanding the limits of core accretion. "This sets a new marker for where the planetary disk processes favor core accretion," Beichman notes.
The challenge of isolating spectral data from the planets was immense, as they are 10,000 times fainter than their star. Ruffio, who led the analysis, developed new techniques to extract the faint signal. Co-lead author Jerry Xuan created detailed atmospheric models to compare with JWST spectra, confirming the presence of sulfur. "The quality of the JWST data is truly revolutionary," Xuan says, "and existing atmospheric model grids were simply not adequate."
The findings will spark new theoretical considerations, as astronomy progresses through observations and subsequent theoretical explanations. Beichman concludes, "Astronomy is driven by observations, and then the theorists have to explain it. This iterative process expands our knowledge, and it's happening every day with JWST and telescopes worldwide."
For more insights, read the extended story on this research from UC San Diego.
