Kepler-226 d
Astrophysical Synthesis & Habitability Characterization
Kepler-226 d is a confirmed terrestrial exoplanet orbiting the star Kepler-226, located approximately 3196.8 light-years (980.14 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0194% across the stellar disk), this world measures 1.22 Earth radii and has a measured mass of 1.98 Earth masses. Combining its mass and radius yields a mean bulk density of 6.01 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.33 g⊕ (13.04 m/s²), and an escape velocity of 14.3 km/s.
In its orbital architecture around Kepler-226, Kepler-226 d completes one full revolution every 8.109 Earth days at a semi-major axis of 0.076 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 102 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 800 K (+527°C / +981°F) and receiving 103.65 S⊕ (~141,061 W/m²), Kepler-226 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-226 is classified as a stellar host with an effective photospheric temperature of 5,571 K, a radius of 0.802 R☉, a mass of 0.904 M☉, an estimated bolometric luminosity of 0.556 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.17 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, Kepler-226 shines at apparent V-band magnitude 15.563 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-226 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-226 d sharing its stellar neighborhood alongside Kepler-226 b, Kepler-226 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-226 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,571 K |
| Stellar Radius | 0.8020 R☉ |
| Stellar Mass | 0.9040 M☉ |
| Bolometric Luminosity | 0.556 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 4.170 Gyr |
| Apparent Magnitude | V: 15.563 · G: 15.403 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.076000 AU |
| Orbital Period | 8.109 days |
| Mean Orbital Velocity | 102 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9200° |
| Mean Bulk Density | 6.01 g/cm³ (14.3 km/s vesc) |
| Insolation Flux | 103.6450 S⊕ (~141,061 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3196.800 LY (980.138 pc) |