The James Webb Space Telescope has provided a detailed view of TOI-5205 b, a Jupiter-sized planet orbiting a small red dwarf (M-dwarf).
The system is often referred to as ‘forbidden’ due to the inexplicable or near-impossible nature of the atmosphere. TOI-5205 b is about the size of Jupiter, but its host star has only about 40% the mass of the Sun.
Because the star is so small, the planet blocks as much as 6% of the star’s light during a transit, making it an ideal candidate for atmospheric research.
Current planetary formation models struggle to explain how such a massive planet could form around such a small host star.
Unexpected atmospheric chemistry
Recent atmospheric analyzes have revealed a surprising chemical profile. The atmosphere contains far fewer heavy elements than expected. Specifically, it has a lower metallicity than the star it orbits, which goes against typical formation patterns.
JWST also detected methane and hydrogen sulfide. According to findings published in the Astronomical magazine, the planet as a whole is about 100 times more metal-rich than the atmosphere appears to be.
“We observed a much lower metallicity than our models predicted for the bulk composition of the planet… This suggests that the heavy elements migrated inward during formation and that the interior and atmosphere are now not mixing,” Kanodia explains.
“In summary, these results suggest a very carbon-rich, oxygen-poor planetary atmosphere,” she added.
The findings imply that heavy elements or metals migrated inward during the planet’s formation and do not mix with the upper atmosphere. The results challenge our understanding of the early stages of giant planet formation.
The research is part of the ‘Red Dwarfs and the Seven Giants’ program, which focuses specifically on rare, massive planets orbiting small M dwarf stars to refine our models of the universe. TOI-5205b was first confirmed in 2023.
