Saturn-sized planet atmosphere contains methane

Penn State University researchers announced on May 21, 2026, the detection of methane in the atmosphere of a Saturn-sized exoplanet with temperatures akin to Earth's, marking a rare find for temperate gas giants. The planet, dubbed TOI-2011 b, orbits its star every 52 days at a distance that keeps its equilibrium temperature around 300 Kelvin—roughly room temperature on Earth, according to the Penn State release. Observations came from NASA's Transiting Exoplanet Surveying Satellite (TESS) and the James Webb Space Telescope (JWST), which analyzed the starlight filtering through the planet's atmosphere during transits. Spectral analysis revealed strong methane absorption lines at 2.2 and 3.3 microns, confirming CH4 as a dominant molecule alongside carbon dioxide and water vapor. Lead researcher Jake Taylor, a Penn State graduate student, noted the signal's clarity: "This is the clearest detection of methane in a temperate exoplanet atmosphere to date" (; ). Unlike hot Jupiters where methane typically breaks down under intense stellar radiation, TOI-2011 b's cooler environment preserves it. The planet's low density—about 0.4 times Jupiter's—suggests a puffed-up atmosphere rich in light gases, per Taylor's team modeling. JWST's NIRSpec and MIRI instruments captured the data during two transits in late 2025. Taylor's group subtracted the host star's spectrum (a K-type dwarf 170 light-years away in Eridanus) to isolate planetary signals, ruling out contaminants like telluric lines or stellar variability (; ). Methane detection here challenges models of atmospheric chemistry. On Earth, CH4 comes from biology or geology; in exoplanets, it could stem from volcanic outgassing, deep interior convection, or delivery via icy planetesimals. Co-author Prof. Suvrath Mahadevan called it "a window into diverse formation histories". This builds on JWST's exoplanet tally: over 50 atmospheres probed since 2022, mostly hot giants. Temperate worlds like TOI-2011 b are scarcer due to smaller signals—transit depths under 0.1%—but JWST's precision (signal-to-noise >10 for methane) unlocks them (; ). No direct imaging yet; the team used transmission spectroscopy. Future JWST cycles target phase curves to map day-night chemistry contrasts and constrain cloud decks. Taylor's paper, accepted to The Astrophysical Journal Letters, details error bars: methane abundance at 1-5% by volume, with CO2 at ~0.1%. Raw spectra are public via MAST archive (; ). Planets like this probe the "radius valley"—a gap in occurrence rates between rocky super-Earths and gaseous sub-Neptunes. Taylor links the methane to inhibited photoevaporation, preserving hydrogen-methane envelopes (; ). Penn State's Habitable Zone Planets team, funded by NASA, flagged TOI-2011 b as prime after TESS detection in 2023. Observations cost ~20 JWST hours; next targets include LHS 1140 b for rocky methane hints. Raw data:. Follow-up proposals due Cycle 3 deadline, August 2026.