Kepler-31 b
Astrophysical Synthesis & Habitability Characterization
Kepler-31 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-31, located approximately 5429.3 light-years (1664.64 parsecs) from the Solar System. First announced in 2011 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1708% across the stellar disk), this world measures 5.5 Earth radii (0.49 Jupiter radii) and has a measured mass of 36.742 Earth masses (0.12 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.22 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.21 g⊕ (11.87 m/s²), and an escape velocity of 28.9 km/s.
In its orbital architecture around Kepler-31, Kepler-31 b completes one full revolution every 20.861 Earth days at a semi-major axis of 0.16 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 83.4 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 781 K (+508°C / +946°F) and receiving 91.47 S⊕ (~124,496 W/m²), Kepler-31 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-31 is classified as a stellar host with an effective photospheric temperature of 6,340 K, a radius of 1.22 R☉, a mass of 1.21 M☉, an estimated bolometric luminosity of 2.158 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.28 Gyr and a metallicity of [Fe/H] = -0.076 dex (near-solar heavy-element abundance). From Earth, Kepler-31 shines at apparent V-band magnitude 15.496 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-31 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-31 b sharing its stellar neighborhood alongside Kepler-31 c, Kepler-31 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-31 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,340 K |
| Stellar Radius | 1.2200 R☉ |
| Stellar Mass | 1.2100 M☉ |
| Bolometric Luminosity | 2.158 L☉ |
| Metallicity [Fe/H] | -0.076 dex |
| Stellar Age | 0.280 Gyr |
| Apparent Magnitude | V: 15.496 · G: 15.224 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.160000 AU |
| Orbital Period | 20.861 days |
| Mean Orbital Velocity | 83.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.8800° |
| Mean Bulk Density | 1.22 g/cm³ (28.9 km/s vesc) |
| Insolation Flux | 91.4740 S⊕ (~124,496 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5429.300 LY (1664.640 pc) |