Kepler-238 d
Astrophysical Synthesis & Habitability Characterization
Kepler-238 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-238, located approximately 5866.7 light-years (1798.75 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0387% across the stellar disk), this world measures 3.07 Earth radii (0.27 Jupiter radii) and has a measured mass of 23.1 Earth masses. Combining its mass and radius yields a mean bulk density of 4.4 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 2.45 g⊕ (24.03 m/s²), and an escape velocity of 30.7 km/s.
In its orbital architecture around Kepler-238, Kepler-238 d completes one full revolution every 13.234 Earth days at a semi-major axis of 0.115 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 94.5 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 888 K (+615°C / +1139°F) and receiving 213.48 S⊕ (~290,546 W/m²), Kepler-238 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-238 is classified as a stellar host with an effective photospheric temperature of 5,751 K, a radius of 1.43 R☉, a mass of 1.229 M☉, an estimated bolometric luminosity of 2.007 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.79 Gyr and a metallicity of [Fe/H] = 0.34 dex (metal-rich relative to the Sun). From Earth, Kepler-238 shines at apparent V-band magnitude 15.297 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-238 system is a multi-planet architecture hosting 5 confirmed worlds, with Kepler-238 d sharing its stellar neighborhood alongside Kepler-238 b, Kepler-238 c, Kepler-238 e, Kepler-238 f.
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-238 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,751 K |
| Stellar Radius | 1.4300 R☉ |
| Stellar Mass | 1.2290 M☉ |
| Bolometric Luminosity | 2.007 L☉ |
| Metallicity [Fe/H] | 0.340 dex |
| Stellar Age | 4.790 Gyr |
| Apparent Magnitude | V: 15.297 · G: 15.024 |
| System Architecture | 1 Star, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.115000 AU |
| Orbital Period | 13.234 days |
| Mean Orbital Velocity | 94.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9500° |
| Mean Bulk Density | 4.4 g/cm³ (30.7 km/s vesc) |
| Insolation Flux | 213.4800 S⊕ (~290,546 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5866.700 LY (1798.750 pc) |