K2-18b
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, initially discovered with the Kepler space telescope, is about eight times the mass of Earth, and is thus classified as a Mini-Neptune. It has a 33-day orbit within the star's habitable zone, meaning that it receives about a similar amount of starlight as the Earth receives from the Sun and could have similar conditions, which allow the existence of liquid water.
| Discovery | |
|---|---|
| Discovery site | Kepler space telescope |
| Discovery date | 2015 |
| Transit | |
| Orbital characteristics | |
| 0.15910+0.00046 −0.00047 au21,380,000 km | |
| Eccentricity | 0.09+0.12 −0.09 |
| 32.940045±0.000100 d | |
| Star | K2-18 |
| Physical characteristics | |
Mean radius | 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) |
In 2019 the presence of water vapour in K2-18b's atmosphere was reported, drawing attention to this system. In 2023, the James Webb Space Telescope detected carbon dioxide and methane in the atmosphere of exoplanet K2-18b. Webb's data suggest the planet might be covered in ocean, with a hydrogen-rich atmosphere. K2-18b has been studied as a potential habitable world that, temperature aside, resembles more a gas planet like Uranus or Neptune than Earth.