Kepler-247 d
Astrophysical Synthesis & Habitability Characterization
Kepler-247 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-247, located approximately 2164.7 light-years (663.71 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.272% across the stellar disk), this world measures 4.5 Earth radii (0.4 Jupiter radii) and has a measured mass of 50 Earth masses (0.16 Jupiter masses). Combining its mass and radius yields a mean bulk density of 3.03 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 2.47 g⊕ (24.22 m/s²), and an escape velocity of 37.3 km/s.
In its orbital architecture around Kepler-247, Kepler-247 d completes one full revolution every 20.474 Earth days at a semi-major axis of 0.14081 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 74.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.102 carries the world between 0.1264 AU at periapsis and 0.1552 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 530 K (+257°C / +495°F) and receiving 15.90 S⊕ (~21,640 W/m²), Kepler-247 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-247 is classified as an orange K-type star of spectral type K with an effective photospheric temperature of 5,094 K, a radius of 0.791 R☉, a mass of 0.884 M☉, an estimated bolometric luminosity of 0.378 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.14 Gyr and a metallicity of [Fe/H] = 0.21 dex (metal-rich relative to the Sun). From Earth, Kepler-247 shines at apparent V-band magnitude 15.199 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-247 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-247 d sharing its stellar neighborhood alongside Kepler-247 b, Kepler-247 c, KOI-884 e.
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-247 |
| Spectral Type | K |
| Effective Temp (Teff) | 5,094 K |
| Stellar Radius | 0.7910 R☉ |
| Stellar Mass | 0.8840 M☉ |
| Bolometric Luminosity | 0.378 L☉ |
| Metallicity [Fe/H] | 0.210 dex |
| Stellar Age | 2.140 Gyr |
| Apparent Magnitude | V: 15.199 · G: 15.047 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.140810 AU |
| Orbital Period | 20.474 days |
| Mean Orbital Velocity | 74.8 km/s |
| Orbital Eccentricity (e) | 0.10200 |
| Orbital Inclination (i) | 88.9340° |
| Mean Bulk Density | 3.03 g/cm³ (37.3 km/s vesc) |
| Insolation Flux | 15.9000 S⊕ (~21,640 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2164.700 LY (663.711 pc) |