Kepler-129 b
Astrophysical Synthesis & Habitability Characterization
Kepler-129 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-129, located approximately 1333.5 light-years (408.85 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0177% across the stellar disk), this world measures 2.4 Earth radii and has a measured mass of 20 Earth masses. Combining its mass and radius yields a mean bulk density of 7.98 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 3.47 g⊕ (34.03 m/s²), and an escape velocity of 32.3 km/s.
In its orbital architecture around Kepler-129, Kepler-129 b completes one full revolution every 15.79 Earth days at a semi-major axis of 0.13 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 89.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.01 (ranging from 0.1287 AU at periapsis to 0.1313 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 910 K (+637°C / +1179°F) and receiving 158.31 S⊕ (~215,454 W/m²), Kepler-129 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-129 is classified as a solar-type yellow star of spectral type G4 V with an effective photospheric temperature of 5,770 K, a radius of 1.653 R☉, a mass of 1.178 M☉, an estimated bolometric luminosity of 2.717 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.43 Gyr and a metallicity of [Fe/H] = 0.29 dex (metal-rich relative to the Sun). From Earth, Kepler-129 shines at apparent V-band magnitude 11.809 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-129 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-129 b sharing its stellar neighborhood alongside Kepler-129 c, Kepler-129 d.
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-129 |
| Spectral Type | G4 V |
| Effective Temp (Teff) | 5,770 K |
| Stellar Radius | 1.6530 R☉ |
| Stellar Mass | 1.1780 M☉ |
| Bolometric Luminosity | 2.717 L☉ |
| Metallicity [Fe/H] | 0.290 dex |
| Stellar Age | 6.430 Gyr |
| Apparent Magnitude | V: 11.809 · G: 11.644 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.130000 AU |
| Orbital Period | 15.79 days |
| Mean Orbital Velocity | 89.6 km/s |
| Orbital Eccentricity (e) | 0.01000 |
| Orbital Inclination (i) | 89.8900° |
| Mean Bulk Density | 7.98 g/cm³ (32.3 km/s vesc) |
| Insolation Flux | 158.3060 S⊕ (~215,454 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1333.500 LY (408.845 pc) |