Astronomers have utilized the Near Infrared Spectrometer (NIRSpec) on the NASA/ESA/CSA James Webb Space Telescope to analyze the atmosphere of TOI-5205b, an extrasolar gas giant orbiting a dim red dwarf star. These groundbreaking observations reveal that the atmosphere is surprisingly deficient in heavy elements, raising intriguing questions regarding the formation and evolution of such “forbidden” alien worlds.
The Jupiter-sized planet TOI-5205b has a surface temperature of 737 K and orbits at a distance of 0.02 astronomical units from its parent star, TOI-5205. Image credit: Sci.News.
TOI-5205b is a short-period gas giant with only 1.03 times the radius and 1.08 times the mass of Jupiter, completing its orbit in just 1.63 days.
Discovered in 2022, this planet orbits the TOI-5205, an M4-type star with approximately 39% of the Sun’s size and mass.
The system, also known as TIC 419411415, is located about 283 light-years away in the constellation Vorissa.
“Short-period Jupiter-mass planets are among the first exoplanets found around Sun-like main-sequence stars, yet their formation processes are still not fully understood,” explained Dr. Caleb Cañas from NASA’s Goddard Space Flight Center.
“The increasing number of short-period giant exoplanets around M dwarfs adds further complexity to gas giant planet formation theories.”
“These worlds are challenging to form through nuclear accretion due to the low disk masses and longer orbital time scales of M dwarfs, which hinder the efficient creation of massive planetary cores necessary for runaway gas accretion.”
“These planets exemplify an extreme formation regime for mid-to-late M-type dwarfs since the significant planet-to-star mass ratio demands a core mass exceeding the estimated dust mass of the protoplanetary disk.”
Astronomers used Webb’s NIRSpec to observe three separate transits of TOI-5205b.
To their surprise, they discovered that the concentration of heavy elements in the planet’s atmosphere, relative to hydrogen, is lower than found in the gas giants of our solar system, including Jupiter. Remarkably, it is even less metallic than its host star.
This finding sets TOI-5205b apart from all other studied giant planets.
Furthermore, the observations revealed the presence of methane and hydrogen sulfide in the planet’s atmosphere, corroborating previous findings.
To better understand their results, the researchers employed an advanced model of the planet’s interior, predicting that TOI-5205b’s overall composition is about 100 times richer in metals than its atmosphere.
“We observed a significantly lower metallicity than what models predicted for the planet’s bulk composition, based on measurements of its mass and radius,” noted Dr. Shubham Kanodia of Carnegie Science.
“This suggests that heavy elements migrated to the interior during formation, indicating that the interior and atmosphere are not currently mixing.”
“In essence, our findings imply that the planet’s atmosphere is notably carbon-rich and oxygen-poor.”
For more information on these findings, check out the latest publication in Astronomy Magazine.
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Caleb I. Cañas et al. 2026. GEMS JWST: TOI-5205b’s transmission spectroscopy reveals significant contamination of the star and a metal-poor atmosphere. A.J. 171, 260; doi: 10.3847/1538-3881/ae4976
Source: www.sci.news
