Kepler-186 d
Astrophysical Synthesis & Habitability Characterization
Kepler-186 d is a confirmed super-earth exoplanet orbiting the star Kepler-186, located approximately 579.2 light-years (177.59 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0739% across the stellar disk), this world measures 1.4 Earth radii and has a measured mass of 2.54 Earth masses. Combining its mass and radius yields a mean bulk density of 5.1 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.3 g⊕ (12.75 m/s²), and an escape velocity of 15.1 km/s.
In its orbital architecture around Kepler-186, Kepler-186 d completes one full revolution every 13.343 Earth days at a semi-major axis of 0.0781 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 63.7 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 379 K (+106°C / +223°F) and receiving 7.20 S⊕ (~9,805 W/m²), Kepler-186 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-186 is classified as a low-mass red dwarf of spectral type M1 with an effective photospheric temperature of 3,788 K, a radius of 0.472 R☉, a mass of 0.478 M☉, an estimated bolometric luminosity of 0.041 L☉. Stellar evolution modeling indicates an estimated stellar age of 4 Gyr and a metallicity of [Fe/H] = -0.28 dex (metal-poor relative to the Sun). From Earth, Kepler-186 shines at apparent V-band magnitude 15.138 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-186 system is a multi-planet architecture hosting 5 confirmed worlds, with Kepler-186 d sharing its stellar neighborhood alongside Kepler-186 b, Kepler-186 c, Kepler-186 e, Kepler-186 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-186 |
| Spectral Type | M1 |
| Effective Temp (Teff) | 3,788 K |
| Stellar Radius | 0.4720 R☉ |
| Stellar Mass | 0.4780 M☉ |
| Bolometric Luminosity | 0.041 L☉ |
| Metallicity [Fe/H] | -0.280 dex |
| Stellar Age | 4.000 Gyr |
| Apparent Magnitude | V: 15.138 · G: 14.599 |
| System Architecture | 1 Star, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.078100 AU |
| Orbital Period | 13.343 days |
| Mean Orbital Velocity | 63.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.1000° |
| Mean Bulk Density | 5.1 g/cm³ (15.1 km/s vesc) |
| Insolation Flux | 7.2040 S⊕ (~9,805 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 579.200 LY (177.594 pc) |