TOI-5205 b shows heavy-element-depleted atmosphere, challenging planet formation models
Updated
Updated · WION · May 2
TOI-5205 b shows heavy-element-depleted atmosphere, challenging planet formation models
4 articles · Updated · WION · May 2
Using the James Webb Space Telescope, an international team found the Jupiter-sized planet orbits an M-dwarf star with just 40% of the Sun’s mass.
Published in The Astronomical Journal, the study detected methane and hydrogen sulphide and found the atmosphere has lower metallicity than the host star, unusual for giant planets.
Researchers say heavy elements may have sunk deep into the planet’s interior, while improved corrections for starspots could sharpen future Webb studies in the GEMS Survey.
Since most stars are M-dwarfs, what other 'impossible' planets are hiding in our own galactic backyard?
What can this planet's bizarre atmosphere-core separation reveal about the hidden interiors of other giant worlds?
If this 'forbidden' planet breaks all the rules, how must we now rethink the birth of entire solar systems?
TOI-5205b’s Carbon-Rich, Metal-Poor Atmosphere Defies Core Accretion Models Around Small Stars
Overview
In 2024, JWST observed TOI-5205b, a gas giant orbiting a small M-dwarf star, revealing a transmission spectrum heavily affected by stellar spots and faculae that masked water vapor signals below 3 microns. Despite this, JWST detected methane and hydrogen sulfide, and atmospheric modeling showed the planet's atmosphere is unusually metal-poor and carbon-rich, contradicting core accretion theory which predicts heavy element enrichment. Interior models suggest a metal-rich bulk, implying a decoupling between the atmosphere and interior. This paradox challenges existing planet formation models and, combined with the rarity of such giants around M dwarfs, drives ongoing efforts to refine stellar contamination corrections and explore new formation mechanisms.