Kepler-129 d
Astrophysical Synthesis & Habitability Characterization
Kepler-129 d is a confirmed gas giant exoplanet orbiting the star Kepler-129, located approximately 1333.5 light-years (408.85 parsecs) from the Solar System. First announced in 2021 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.6 Earth radii (1.12 Jupiter radii) and has a measured mass of 2637.976 Earth masses (8.3 Jupiter masses). Combining its mass and radius yields a mean bulk density of 7.27 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 16.62 g⊕ (162.99 m/s²), and an escape velocity of 161.9 km/s.
In its orbital architecture around Kepler-129, Kepler-129 d completes one full revolution every 2646 Earth days (7.24Julian years) at a semi-major axis of 4 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 16.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.15 carries the world between 3.4 AU at periapsis and 4.6 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 179 K (-94°C / -137°F) and an incident flux of 0.18 S⊕ (~247 W/m²), surface water and volatile species on Kepler-129 d would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
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 d sharing its stellar neighborhood alongside Kepler-129 b, Kepler-129 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: W. M. Keck Observatory · 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) | 4.000000 AU |
| Orbital Period | 2646 days |
| Mean Orbital Velocity | 16.4 km/s |
| Orbital Eccentricity (e) | 0.15000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 7.27 g/cm³ (161.9 km/s vesc) |
| Insolation Flux | 0.1818 S⊕ (~247 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1333.500 LY (408.845 pc) |