The star
The star
Kepler-138
- Type
- M1 V
- Surface
- ≈ 3,841 K
- Size
- 0.54 × the Sun
- Mass
- 0.54 × the Sun
- Brightness
- 0.056 × the Sun
- Habitable zone
- 0.193–0.491 AU
The planets
Kepler-138
Kepler-138 b
- Year
- 10.31 days
- Distance from star
- 0.0753 AU
- Mass
- 0.07 Earths
- Size
- 0.64 × Earth
- Temperature
- ≈ 452 K (+179 °C)
- Found
- 2014, transit (Kepler)
Kepler-138
Kepler-138 c
- Year
- 13.78 days
- Distance from star
- 0.0913 AU
- Mass
- 2.3 Earths
- Size
- 1.5 × Earth
- Temperature
- ≈ 410 K (+137 °C)
- Found
- 2014, transit (Kepler)
Kepler-138
Kepler-138 d
- Year
- 23.09 days
- Distance from star
- 0.129 AU
- Mass
- 2.1 Earths
- Size
- 1.5 × Earth
- Temperature
- ≈ 345 K (+72 °C)
- Found
- 2014, transit (Kepler)
Kepler-138
Kepler-138 e
- Year
- 38.23 days
- Distance from star
- 0.18 AU
- Mass
- 0.43 Earths
- Size
- 0.8 × Earth
- Temperature
- ≈ 292 K (+19 °C)
- Found
- 2022, transit timing variations (Multiple Observatories)
Masses found by the wobble method are minimums, because the orbit's tilt is unknown. Temperatures are equilibrium estimates for a bare planet, before any atmosphere.
How we know
The shadow
The planet passes in front of its star and dims it by a fraction of a percent, every orbit. The dip gives the planet's size and year.
Early and late
A known planet arrives early or late for its transits, betraying the pull of another, unseen planet.
Sources
- Planet and star parameters: NASA Exoplanet Archive, Planetary Systems Composite Parameters, retrieved 1 Nov 2026. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with NASA under the Exoplanet Exploration Program.
- Position: HYG Database v4.1 (CC BY-SA 4.0).
- Habitable zone: a simple estimate from the star's brightness (√L × 0.95 to 1.67 AU), shown as a guide.