ExoAtmospheres
IAC community database for exoplanet atmospheric observations
K2-18 b
| Planet status | Confirmed |
|---|---|
| Planet type | Temperate Sub-Neptune |
| Period | 32.939623 d |
| Mass | 0.0281 MJ 8.93018 M⊕ |
| Radius | 0.211 RJ 2.3632 R⊕ |
| Semi major axis | 0.1429 AU |
| Star name | K2-18 |
| Star distance | 38.07 pc |
| Star teff | 3457 K |
| Star radius | 0.41 R☉ |
| Temperature (calculated) | 284 K |
| V | 13.5 mag |
| J | 9.763 mag |
| K | 8.899 mag |
| Alternate names | EPIC 201912552 b, 2MASS J11301450+0735180 b, EPIC 201912552.01, WISE J113014.45+073516.8 b |
| Exoplanet Encyclopaedia |  |
Molecules
Molecular ratios: C/O, etc...: Detection CH4: Detection
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JWST-NIRISS | The Atmospheric Composition of Sub-Neptune K2-18 b and Implications for its Formation2025, Gareb Fernández-Rodríguez, Giuseppe Morello et al. |
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CO2: Detection CH4: Detection
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JWST-NIRSpec | A water-rich interior in the temperate sub-Neptune K2-18 b revealed by JWST2025, Renyu Hu, Aaron Bello-Arufe et al. |
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DMS: Upper limit DMDS: Upper limit
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JWST-MIRI | Insufficient evidence for DMS and DMDS in the atmosphere of K2-18 b. From a joint analysis of JWST NIRISS, NIRSpec, and MIRI observations2025, R. Luque, C. Piaulet-Ghorayeb et al. |
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DMS: Detection DMDS: Detection
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JWST-MIRI | New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI2025, Nikku Madhusudhan, Savvas Constantinou et al. |
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CH4: Detection CO2: Upper limit
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JWST-NIRSpec | A Comprehensive Reanalysis of K2-18 b's JWST NIRISS+NIRSpec Transmission Spectrum2025, Stephen P. Schmidt, Ryan J. MacDonald et al. |
No DMS evidences |
CH4: Upper limit NH3: Upper limit
|
G-B: High resolution IR | High-resolution Spectroscopic Reconnaissance of a Temperate Sub-Neptune2024, Samuel H. C. Cabot, Nikku Madhusudhan et al. |
One transit with IGRINS. Marginal detection of CH4 (2.2σ) |
CH4: Detection CO2: Detection NH3: No detection
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JWST-NIRISS | Carbon-bearing Molecules in a Possible Hycean Atmosphere2023, Nikku Madhusudhan, Subhajit Sarkar et al. |
Suggest potential signs of DMS |
CH4: Detection
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HST WFC3 | Methane as a dominant absorber in the habitable-zone sub-Neptune K2-18 b2020, Bruno Bézard, Benjamin Charnay et al. |
Modelling paper arguing for CH4 instead of H2O detection |
H: Upper limit
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HST STIS | The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b2020, dos Santos, Leonardo A., Ehrenreich, David et al. |
Hints of Ly-a absorption from a partial transit observation. |
H2O: Detection
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HST WFC3 | Water Vapor and Clouds on the Habitable-zone Sub-Neptune Exoplanet K2-18b2019, Benneke, Björn, Wong, Ian et al. |
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H2O: Detection
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HST WFC3 | Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b2019, Tsiaras, Angelos, Waldmann, Ingo P. et al. |
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DMS: Detection DMDS: Detection
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JWST-MIRI | Astro-ph arXiv:2609.05264 | Bayesian evidence for Chloroethane |