Space telescope James Webb observed the atmosphere of a giant exoplanet orbiting a red dwarf star. The planet TOI-5205 b is similar in size to Júpiter and is about 280 light-years away from Terra. The discovery reveals details that do not fit current models of planetary formation.
An international team led by astrophysicist Caleb Cañas of NASA’s Goddard Space Flight Center published the results in April 2026 at The Astronomical Journal. The work is part of a larger program investigating gas giants around red dwarfs, known as GEMS systems. Astronomers used James Webb’s transit spectroscopy instrument to examine the planet during three passes in front of the star.
The planet that defies formation rules
TOI-5205 b was initially identified as a candidate by NASA’s TESS satellite and confirmed in 2023. Ele orbits an M-type star with about 40% the mass of Sol. Modelos of core accretion predicts that such small stars would not have enough material in their protoplanetary disk to form a gas giant the size of Júpiter.
This disproportion between the size of the planet and that of the host star already made the system unusual. Astrônomos call these cases forbidden planets because known physics indicated that formation should not occur in this way. The planet blocks about 6% of the star’s light during transit, which facilitates detailed observations of the atmosphere.
Data from James Webb confirmed the transit and made it possible to separate planetary signals from stellar contamination. The active star generated variations that researchers needed to correct for to isolate the atmospheric signature.
Atmospheric details revealed by James Webb
The spectral analysis showed that the atmosphere of TOI-5205 b has a low concentration of heavy elements, that is, metals in the astronomical sense, which are elements heavier than hydrogen and helium. The measured metallicity was below that of the host star itself.
This characteristic contradicts the expectation that giant planets inherit and often enrich the chemical composition of the star where they form. In known systems, like ours, Júpiter has more metals than Sol. In the case of TOI-5205 b, the opposite occurs.
The spectra indicated the presence of methane and hydrogen sulfide. Outros compounds did not appear with significant strength after data processing. The estimated surface temperature is around 737 K, with a short orbit approximately 0.02 AU from the star.
- The planet has a radius and mass compatible with Júpiter
- The host star has about 40% of the solar mass
- Three transits were observed to construct the transmission spectrum
- Stellar contamination required detailed modeling to extract planetary signals
- Methane was detected with high confidence on multiple visits
- Hydrogen sulfide appeared with a more moderate signal
Impact on theoretical models of giant planets
The combination of two challenges — the formation of a giant around a low-mass red dwarf and an atmosphere poorer in metals than the star — puts pressure on current paradigms. Anãs red ones represent about 70% of the stars in Via Láctea, which makes it important to understand whether they can harbor this type of planet.
The core accretion mechanism predicts that a rocky core accumulates gas and results in planets with metallicity equal to or greater than that of the star. The observation of TOI-5205 b suggests that alternative processes or special conditions in the protoplanetary disk may be at play.
Researchers highlight that the detection of methane and hydrogen sulfide offers clues about atmospheric chemistry, possibly indicating an atmosphere rich in carbon and poor in oxygen. Essas Information helps refine simulations of planetary formation and evolution.
Observations that open new questions
The Red Dwarfs and the Seven Giants program, which includes this study, plans to examine more systems similar to James Webb. The goal is to map how many gas giants orbit red dwarfs and how their atmospheres behave.
The transit spectroscopy technique relies on starlight passing through the planet’s atmosphere. In the case of TOI-5205 b, the depth of the transit allowed good sensitivity despite the stellar activity.
Astronomers continue to validate correction methods for star spot and facula contamination. Resultados Futures on other planets from the same program may confirm or adjust initial conclusions about TOI-5205 b.
What’s next for exoplanet research
Red dwarfs are priority targets in the search for habitable worlds because they are common and have nearby habitable zones. Entender The formation of giants in these stars helps to contextualize the frequency of systems with smaller planets.
The study reinforces the need to update theoretical models with real data from James Webb. Additional Observações at different wavelengths could reveal more about the internal structure and history of TOI-5205 b.
The scientific community follows the case as an example of how new technologies question established ideas. Cada new data expands the catalog of possible scenarios for the formation of planets in the galaxy.