Star system, 660 light-years
K2-138 and its six planets
K2-138 b is an exoplanet 1.51 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
K2-138 is a star of spectral type G8 V, 660 light-years from us, with six 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
K2-138 b
K2-138 b is an exoplanet 1.51 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 1.51 × Earth's measured
- Mass
- 3.1 times Earth's measured
- One year
- 2.35309 days measured
- Distance from its star
- 0.03385 au from the Archive
- Temperature of a bare ball there
- 1,173 K computed, not measured
- Starlight, against Earth's
- 451 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2017. Its orbit is closer to its star than the habitable zone computed for it.
See K2-138 b in 3D · The picture is an artist's impression.
K2-138 c
K2-138 c is an exoplanet 2.299 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 2.299 × Earth's measured
- Mass
- 6.31 times Earth's measured
- One year
- 3.56004 days measured
- Distance from its star
- 0.04461 au from the Archive
- Temperature of a bare ball there
- 1,022 K computed, not measured
- Starlight, against Earth's
- 260 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2017. Its orbit is closer to its star than the habitable zone computed for it.
See K2-138 c in 3D · The picture is an artist's impression.
K2-138 d
K2-138 d is an exoplanet 2.39 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 2.39 × Earth's measured
- Mass
- 7.92 times Earth's measured
- One year
- 5.40479 days measured
- Distance from its star
- 0.05893 au from the Archive
- Temperature of a bare ball there
- 889 K computed, not measured
- Starlight, against Earth's
- 149 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2017. Its orbit is closer to its star than the habitable zone computed for it.
See K2-138 d in 3D · The picture is an artist's impression.
K2-138 e
K2-138 e is an exoplanet 3.39 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 3.39 × Earth's measured
- Mass
- 12.97 times Earth's measured
- One year
- 8.26146 days measured
- Distance from its star
- 0.0782 au from the Archive
- Temperature of a bare ball there
- 772 K computed, not measured
- Starlight, against Earth's
- 84.5 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2017. Its orbit is closer to its star than the habitable zone computed for it.
See K2-138 e in 3D · The picture is an artist's impression.
K2-138 f
K2-138 f is an exoplanet 2.904 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 2.904 × Earth's measured
- Mass
- 1.63 times Earth's measured
- One year
- 12.7576 days measured
- Distance from its star
- 0.10447 au from the Archive
- Temperature of a bare ball there
- 668 K computed, not measured
- Starlight, against Earth's
- 47.4 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2017. Its orbit is closer to its star than the habitable zone computed for it.
See K2-138 f in 3D · The picture is an artist's impression.
K2-138 g
K2-138 g is an exoplanet 3.013 times Earth's width, 660 light-years away, orbiting closer to its star than the habitable zone we compute for it.
- Width
- 3.013 × Earth's measured
- Mass
- 4.32 times Earth's measured
- One year
- 41.968 days measured
- Distance from its star
- 0.23109 au from the Archive
- Temperature of a bare ball there
- 449 K computed, not measured
- Starlight, against Earth's
- 9.68 × computed
It was found as a small, regular dip in its star's light each time it crosses in front of it in 2021. Its orbit is closer to its star than the habitable zone computed for it.
See K2-138 g in 3D · The picture is an artist's impression.
The star
- Surface temperature
- 5,356 K
- Width
- 0.863 × the Sun's
- Mass
- 0.935 × the Sun's
- Spectral type
- G8 V
- Distance
- 660 light-years
- Habitable zone, computed
- 0.7004 to 1.251 au from the star