Kepler-229 d
Astrophysical Synthesis & Habitability Characterization
Kepler-229 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-229, located approximately 2694.9 light-years (826.27 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.2351% across the stellar disk), this world measures 3.85 Earth radii (0.34 Jupiter radii) and has a measured mass of 14.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.37 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.96 g⊕ (9.41 m/s²), and an escape velocity of 21.5 km/s.
In its orbital architecture around Kepler-229, Kepler-229 d completes one full revolution every 41.195 Earth days at a semi-major axis of 0.22 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 58.1 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 439 K (+166°C / +331°F) and receiving 6.16 S⊕ (~8,386 W/m²), Kepler-229 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-229 is classified as a stellar host with an effective photospheric temperature of 5,120 K, a radius of 0.728 R☉, a mass of 0.808 M☉, an estimated bolometric luminosity of 0.327 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.04 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, Kepler-229 shines at apparent V-band magnitude 16.22 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-229 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-229 d sharing its stellar neighborhood alongside Kepler-229 b, Kepler-229 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-229 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,120 K |
| Stellar Radius | 0.7280 R☉ |
| Stellar Mass | 0.8080 M☉ |
| Bolometric Luminosity | 0.327 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 2.040 Gyr |
| Apparent Magnitude | V: 16.220 · G: 15.827 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.220000 AU |
| Orbital Period | 41.195 days |
| Mean Orbital Velocity | 58.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9600° |
| Mean Bulk Density | 1.37 g/cm³ (21.5 km/s vesc) |
| Insolation Flux | 6.1620 S⊕ (~8,386 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2694.900 LY (826.265 pc) |