Kepler-381 d
Astrophysical Synthesis & Habitability Characterization
Kepler-381 d is a confirmed terrestrial exoplanet orbiting the star Kepler-381, located approximately 871.9 light-years (267.32 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.002% across the stellar disk), this world measures 1.067 Earth radii and has a measured mass of 1.23 Earth masses. Combining its mass and radius yields a mean bulk density of 5.58 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 12 km/s.
In its orbital architecture around Kepler-381, Kepler-381 d completes one full revolution every 8.256 Earth days at a semi-major axis of 0.08364 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 110.2 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 1387 K (+1114°C / +2037°F) and receiving 436.70 S⊕ (~594,349 W/m²), Kepler-381 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-381 is classified as a stellar host with an effective photospheric temperature of 6,197 K, a radius of 2.188 R☉, a mass of 1.198 M☉, an estimated bolometric luminosity of 6.334 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.57 Gyr and a metallicity of [Fe/H] = -0.32 dex (metal-poor relative to the Sun). From Earth, Kepler-381 shines at apparent V-band magnitude 10.47 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-381 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-381 d sharing its stellar neighborhood alongside Kepler-381 b, Kepler-381 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-381 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,197 K |
| Stellar Radius | 2.1880 R☉ |
| Stellar Mass | 1.1980 M☉ |
| Bolometric Luminosity | 6.334 L☉ |
| Metallicity [Fe/H] | -0.320 dex |
| Stellar Age | 2.570 Gyr |
| Apparent Magnitude | V: 10.470 · G: 10.546 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.083640 AU |
| Orbital Period | 8.256 days |
| Mean Orbital Velocity | 110.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.4400° |
| Mean Bulk Density | 5.58 g/cm³ (12 km/s vesc) |
| Insolation Flux | 436.7000 S⊕ (~594,349 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 871.900 LY (267.323 pc) |