Back K2-18b Afrikaans K2-18b AN K2-18b Arabic K2-18 b Byelorussian কে২-১৮বি Bengali/Bangla K2-18b Catalan K2-18b Czech K2-18b Danish K2-18b German K2-18b Greek
.jpg) | |
| Discovery | |
|---|---|
| Discovery site | Kepler space telescope |
| Discovery date | 2015 |
| Transit | |
| Orbital characteristics[1] | |
| 0.15910+0.00046 −0.00047 au21,380,000 km | |
| Eccentricity | 0.09+0.12 −0.09[2] |
| 32.940045±0.000100 d | |
| 354.3+46.4 −33.8°[3] | |
| Star | K2-18 |
| Physical characteristics | |
| 2.610±0.087 R🜨 | |
| Mass | 8.63±1.35 M🜨 |
Mean density | 2.67+0.52 −0.47 g/cm3 |
| 12.43+2.17 −2.07 m/s2 | |
| Temperature | 265 ± 5 K (−8 ± 5 °C) |
K2-18b, also known as EPIC 201912552 b, is an exoplanet orbiting the red dwarf K2-18, located 124 light-years (38 pc) away from Earth. The planet is a sub-Neptune about 2.6 times the radius of Earth, with a 33-day orbit within the star's habitable zone; it receives approximately a similar amount of light as the Earth receives from the Sun. Initially discovered with the Kepler space telescope, it was later observed by the James Webb Space Telescope (JWST) in order to study the planet's atmosphere.
In 2019, the presence of water vapour in K2-18b's atmosphere was reported, drawing scientific attention to this system. In 2023, the JWST detected carbon dioxide and methane in the atmosphere of K2-18b. JWST’s data has been variously interpreted as indicating a water ocean planet with a hydrogen-rich atmosphere, and a gas-rich mini-Neptune. K2-18b has been studied as a potential habitable world that, temperature aside, more closely resembles an ice giant like Uranus or Neptune than Earth.
In 2025, the atmosphere of K2-18b was reported to contain dimethyl sulfide (DMS), a chemical that could serve as a biosignature on exoplanets, in quantities 20 times higher than on Earth. As the molecule is short-lived, the concentration is highly suggestive that DMS is being replenished.[4] Ethan Siegel criticised this statement for its bold claims and flawed analysis,[5] and other scientists point to lab experiments that can produce DMS without life.[6][7]
- ^ Benneke et al. 2019, p. 4.
- ^ Blain, Charnay & Bézard 2021, p. 2.
- ^ Martin 2024.
- ^ Nikku Madhusudhan; Savvas Constantinou; Måns Holmberg; Subhajit Sarkar; Anjali A. A. Piette; Julianne I. Moses (17 April 2025). "New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI". The Astrophysical Journal Letters. 983 (2): L40. arXiv:2504.12267v1. Bibcode:2025ApJ...983L..40M. doi:10.3847/2041-8213/adc1c8.
The spectrum shows multiple spectral features between ∼6 and 11 μm that are best explained by a combination of DMDS and DMS in the atmosphere
- ^ Siegel, Ethan (22 April 2025). "The evidence for biosignatures on K2-18b is flimsy, at best". Big Think. Retrieved 23 April 2025.
- ^ Cite error: The named reference
:0was invoked but never defined (see the help page). - ^ Reed, Nathan W.; Shearer, Randall L.; McGlynn, Shawn Erin; Wing, Boswell A.; Tolbert, Margaret A.; Browne, Eleanor C. (October 2024). "Abiotic Production of Dimethyl Sulfide, Carbonyl Sulfide, and Other Organosulfur Gases via Photochemistry: Implications for Biosignatures and Metabolic Potential". The Astrophysical Journal. 973 (2): L38. Bibcode:2024ApJ...973L..38R. doi:10.3847/2041-8213/ad74da. ISSN 0004-637X.
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