Kepler-431 c
Astrophysical Synthesis & Habitability Characterization
Kepler-431 c is a confirmed sub-earth exoplanet orbiting the star Kepler-431, located approximately 1586.9 light-years (486.55 parsecs) from the Solar System. First announced in 2015 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0031% across the stellar disk), this world measures 0.668 Earth radii and has a measured mass of 0.229 Earth masses. Combining its mass and radius yields a mean bulk density of 4.24 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.51 g⊕ (5 m/s²), and an escape velocity of 6.5 km/s.
In its orbital architecture around Kepler-431, Kepler-431 c completes one full revolution every 8.703 Earth days at a semi-major axis of 0.0847 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 105.9 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 951 K (+678°C / +1252°F) and receiving 415.55 S⊕ (~565,557 W/m²), Kepler-431 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-431 is classified as a stellar host with an effective photospheric temperature of 6,004 K, a radius of 1.092 R☉, a mass of 1.071 M☉, an estimated bolometric luminosity of 1.39 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.34 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, Kepler-431 shines at apparent V-band magnitude 12.139 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-431 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-431 c sharing its stellar neighborhood alongside Kepler-431 b, Kepler-431 d.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-431 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,004 K |
| Stellar Radius | 1.0920 R☉ |
| Stellar Mass | 1.0710 M☉ |
| Bolometric Luminosity | 1.39 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 4.340 Gyr |
| Apparent Magnitude | V: 12.139 · G: 11.929 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.084700 AU |
| Orbital Period | 8.703 days |
| Mean Orbital Velocity | 105.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 82.3500° |
| Mean Bulk Density | 4.24 g/cm³ (6.5 km/s vesc) |
| Insolation Flux | 415.5450 S⊕ (~565,557 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1586.900 LY (486.546 pc) |