NASA (Exoplanet Catalog artwork)K2-18b
The possible ocean world at the centre of the biosignature debate
Overview
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.
Source: Wikipedia
NASA: K2-18 b is a super Earth exoplanet that orbits a M-type star. Its mass is 8.92 Earths, it takes 32.9 days to complete one orbit of its star, and is 0.1429 AU from its star. Its discovery was announced in 2015.
Why it matters
- Water vapour was reported in its atmosphere in 2019, the first for a habitable-zone planet.
- JWST found methane and carbon dioxide in 2023, consistent with a 'Hycean' ocean under a hydrogen sky.
- A 2025 claim of dimethyl sulfide, a gas made by life on Earth, was quickly challenged by reanalyses.
NASA puts it this way: “K2-18 b is a super Earth exoplanet that orbits an M-type star. Its mass is 8.92 Earths, it takes 32.9 days to complete one orbit of its star, and is 0.1429 AU from its star. Its discovery was announced in 2015.”
Discovery & system
- Discovered
- 2015 · Transit · K2
- Discovery paper
- Montet et al. 2015
- Discoverers
- Kepler Space Telescope
- Host star
- K2-18 · M2.5 V · 3,457 K · 0.36 M☉
- System
- 2 known planets
- Siblings
- K2-18 c
The system
| World | Period | Distance | Radius | Mass | Temp. |
|---|---|---|---|---|---|
| K2-18 c ? | 8.96 d | 0.06 AU | 2.65 R⊕ | ≥ 7.51 M⊕ | 363 K |
| K2-18 b | 32.9 d | 0.143 AU | 2.37 R⊕ | 8.92 M⊕ | 284 K |
By the numbers
- Radius
- 2.37 R⊕15,099 km
- Mass
- 8.92 M⊕53.27 ×10²⁴ kg
- Orbital period
- 32.9 d0.09 yr
- Distance from star
- 0.143 AU21 million km
- Eccentricity
- 0.2elliptical
- Equilibrium temp.
- 284 K11 °C
- Starlight received
- 1 × Earth
- Distance from Earth
- 124 ly38 pc
- Density
- 4.11 g/cm³0.75 × Earth
Sources
Image: NASA (Exoplanet Catalog artwork) · NASA media: generally free of copyright · image page
Text: Wikipedia (CC BY-SA 4.0). Taglines and highlights are editorial.