Kepler-126 d
Astrophysical Synthesis & Habitability Characterization
Kepler-126 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-126, located approximately 774.3 light-years (237.4 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0285% across the stellar disk), this world measures 2.5 Earth radii and has a measured mass of 54.59 Earth masses (0.17 Jupiter masses). Combining its mass and radius yields a mean bulk density of 19.26 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 8.73 g⊕ (85.61 m/s²), and an escape velocity of 52.3 km/s.
In its orbital architecture around Kepler-126, Kepler-126 d completes one full revolution every 100.283 Earth days at a semi-major axis of 0.448 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 48.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.02 (ranging from 0.439 AU at periapsis to 0.457 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 475 K (+202°C / +396°F) and receiving 14.71 S⊕ (~20,026 W/m²), Kepler-126 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-126 is classified as a stellar host with an effective photospheric temperature of 6,239 K, a radius of 1.358 R☉, a mass of 1.108 M☉, an estimated bolometric luminosity of 2.507 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.39 Gyr and a metallicity of [Fe/H] = -0.16 dex (metal-poor relative to the Sun). From Earth, Kepler-126 shines at apparent V-band magnitude 10.505 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-126 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-126 d sharing its stellar neighborhood alongside Kepler-126 b, Kepler-126 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-126 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,239 K |
| Stellar Radius | 1.3580 R☉ |
| Stellar Mass | 1.1080 M☉ |
| Bolometric Luminosity | 2.507 L☉ |
| Metallicity [Fe/H] | -0.160 dex |
| Stellar Age | 3.390 Gyr |
| Apparent Magnitude | V: 10.505 · G: 10.454 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.448000 AU |
| Orbital Period | 100.283 days |
| Mean Orbital Velocity | 48.6 km/s |
| Orbital Eccentricity (e) | 0.02000 |
| Orbital Inclination (i) | 89.5000° |
| Mean Bulk Density | 19.26 g/cm³ (52.3 km/s vesc) |
| Insolation Flux | 14.7140 S⊕ (~20,026 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 774.300 LY (237.401 pc) |