The star
The star
Kepler-121
- Type
- yellow star
- Surface
- ≈ 5,311 K
- Size
- 0.70 × the Sun
- Mass
- 0.86 × the Sun
- Brightness
- 0.336 × the Sun
- Habitable zone
- 0.447–1.07 AU
The planets
Kepler-121
Kepler-121 b
- Year
- 3.18 days
- Distance from star
- 0.039 AU
- Mass
- 6.1 Earths
- Size
- 2.3 × Earth
- Temperature
- ≈ 997 K (+724 °C)
- Found
- 2014, transit (Kepler)
Kepler-121
Kepler-121 c
- Year
- 41.01 days
- Distance from star
- 0.216 AU
- Mass
- 5.8 Earths
- Size
- 2.3 × Earth
- Temperature
- ≈ 425 K (+152 °C)
- Found
- 2014, transit (Kepler)
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.
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.