Star system, 120 light-years
K2-18 and its two planets
K2-18 b is an exoplanet 2.37 times Earth's width, 120 light-years away, orbiting at the edge of its star's computed habitable zone.
K2-18 is a star of spectral type M2.5 V, 120 light-years from us, with two known planets. This page takes them one at a time.
Drawn at the system's own scale, every orbit from the Archive's numbers.
What is measured, what is computed, what is imagined.
measured The period, and where the table says so the width and the mass, by the method named in each section.
computed Anything marked computed: the size of an orbit where Kepler's third law corrects the table, the temperature of a bare ball at that distance, the starlight received, and the habitable zone.
imagined The picture is an artist's impression. Nobody has seen the surface of a planet of another star: its colour, clouds and land are not known, and the share picture says so in its corner.
The planets
K2-18 c
K2-18 c is an exoplanet about 2.65 times Earth's width (a size estimated from its mass), 120 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 2.65 × Earth's estimated
- Mass
- at least 7.51 times Earth's measured
- One year
- 8.962 days measured
- Distance from its star
- 0.06 au from the Archive
- Temperature of a bare ball there
- 415 K computed, not measured
- Starlight, against Earth's
- 7.03 × computed
It was found by the back-and-forth wobble its pull puts into its star's motion, seen as a shift in the colour of the star's light in 2017. Its orbit is closer to its star than the habitable zone computed for it.
See K2-18 c in 3D · The picture is an artist's impression.
K2-18 b
K2-18 b is an exoplanet 2.37 times Earth's width, 120 light-years away, orbiting at the edge of its star's computed habitable zone.
- Width
- 2.37 × Earth's measured
- Mass
- 8.92 times Earth's measured
- One year
- 32.9396 days measured
- Distance from its star
- 0.1429 au from the Archive
- Temperature of a bare ball there
- 269 K computed, not measured
- Starlight, against Earth's
- 1.24 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2015. Its orbit lies at the edge of the conservative habitable zone computed for its star.
See K2-18 b in 3D · The picture is an artist's impression.
The star
- Surface temperature
- 3,457 K
- Width
- 0.411 × the Sun's
- Mass
- 0.359 × the Sun's
- Spectral type
- M2.5 V
- Distance
- 120 light-years
- Habitable zone, computed
- 0.1649 to 0.3209 au from the star