JWST images reveal CO2 and high metallicity in super-Jupiter 29 Cyg b, hinting at disk formation

29 Cyg b is a massive companion to the star 29 Cygni, with a mass near the boundary between giant planets and brown dwarfs. Using the James Webb Space Telescope, astronomers directly imaged the planet and detected strong absorption from carbon monoxide and carbon dioxide in its atmosphere. The strength of the CO2 feature compared to CO indicates that 29 Cyg b is enriched in heavy elements, or metals, relative to its host star.

This enhanced metallicity suggests that 29 Cyg b likely formed within the protoplanetary disk around its star, accumulating metal-rich material, rather than forming through disk fragmentation or capture like more massive companions. Measurements also show that the planet's orbit is aligned with the star's rotation, supporting the idea of formation in the disk. These findings show that planet formation around massive stars can produce objects as large as 29 Cyg b, and that high metallicity is a key signature of this process.

The results provide new evidence for how super-Jupiter planets form and highlight the power of JWST in studying the atmospheres and origins of massive exoplanets.

Key findings
- JWST directly imaged CO2 and CO in 29 Cyg b's atmosphere
- The planet is enriched in heavy elements compared to its star
- Evidence supports formation in the protoplanetary disk
- The planet's orbit is aligned with the star's rotation
- High metallicity is a signature of disk-based planet formation

Scientific study

Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk (external link)