The star
The star
Kepler-399
- Type
- yellow star
- Surface
- ≈ 5,502 K
- Size
- 0.68 × the Sun
- Mass
- 0.90 × the Sun
- Brightness
- 0.382 × the Sun
- Habitable zone
- 0.471–1.12 AU
The planets
Kepler-399
Kepler-399 b
- Year
- 14.43 days
- Distance from star
- 0.103 AU
- Mass
- 0.84 Earths
- Size
- 0.96 × Earth
- Temperature
- ≈ 773 K (+500 °C)
- Found
- 2014, transit (Kepler)
Kepler-399
Kepler-399 c
- Year
- 26.68 days
- Distance from star
- 0.155 AU
- Mass
- 2.6 Earths
- Size
- 1.4 × Earth
- Temperature
- ≈ 630 K (+357 °C)
- Found
- 2014, transit (Kepler)
Kepler-399
Kepler-399 d
- Year
- 58.03 days
- Distance from star
- 0.261 AU
- Mass
- 4.2 Earths
- Size
- 1.9 × Earth
- Temperature
- ≈ 486 K (+213 °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.