Kepler-31 d
Astrophysical Synthesis & Habitability Characterization
Kepler-31 d 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 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0859% across the stellar disk), this world measures 3.9 Earth radii (0.35 Jupiter radii) and has a measured mass of 2161.244 Earth masses (6.8 Jupiter masses). Combining its mass and radius yields a mean bulk density of 200.9 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 142.09 g⊕ (1393.43 m/s²), and an escape velocity of 263.3 km/s.
In its orbital architecture around Kepler-31, Kepler-31 d completes one full revolution every 87.645 Earth days at a semi-major axis of 0.4 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 49.7 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 484 K (+211°C / +412°F) and receiving 11.80 S⊕ (~16,060 W/m²), Kepler-31 d 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 d sharing its stellar neighborhood alongside Kepler-31 b, Kepler-31 c.
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) | 0.400000 AU |
| Orbital Period | 87.645 days |
| Mean Orbital Velocity | 49.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.8900° |
| Mean Bulk Density | 200.9 g/cm³ (263.3 km/s vesc) |
| Insolation Flux | 11.8000 S⊕ (~16,060 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5429.300 LY (1664.640 pc) |