Overview
- JWST transit spectra of TOI-5205 b, reported in The Astronomical Journal, show its atmosphere has fewer heavy elements than its host star.
- Most giant planets have atmospheres more metal-rich than their stars, so this reversal breaks with standard formation expectations.
- The spectra reveal methane and hydrogen sulfide, which mark a chemically complex yet metal-poor atmosphere.
- Interior models point to heavy elements being sequestered deep inside the planet with little mixing into the air.
- The Jupiter-mass planet circles a small red dwarf about 375 times its mass and blocks roughly six percent of its light, giving JWST an unusually strong signal to probe how such giants arise around M-dwarfs.