Kepler-306 d
Astrophysical Synthesis & Habitability Characterization
Kepler-306 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-306, located approximately 2529.9 light-years (775.68 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0992% across the stellar disk), this world measures 2.47 Earth radii and has a measured mass of 6.66 Earth masses. Combining its mass and radius yields a mean bulk density of 2.44 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.4 km/s.
In its orbital architecture around Kepler-306, Kepler-306 d completes one full revolution every 17.327 Earth days at a semi-major axis of 0.12 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 75.3 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 535 K (+262°C / +504°F) and receiving 21.98 S⊕ (~29,919 W/m²), Kepler-306 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-306 is classified as a stellar host with an effective photospheric temperature of 4,954 K, a radius of 0.719 R☉, a mass of 0.75 M☉, an estimated bolometric luminosity of 0.279 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.63 Gyr and a metallicity of [Fe/H] = -0.13 dex (metal-poor relative to the Sun). From Earth, Kepler-306 shines at apparent V-band magnitude 15.575 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-306 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-306 d sharing its stellar neighborhood alongside Kepler-306 b, Kepler-306 c, Kepler-306 e.
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-306 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,954 K |
| Stellar Radius | 0.7190 R☉ |
| Stellar Mass | 0.7500 M☉ |
| Bolometric Luminosity | 0.279 L☉ |
| Metallicity [Fe/H] | -0.130 dex |
| Stellar Age | 2.630 Gyr |
| Apparent Magnitude | V: 15.575 · G: 15.552 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.120000 AU |
| Orbital Period | 17.327 days |
| Mean Orbital Velocity | 75.3 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.0000° |
| Mean Bulk Density | 2.44 g/cm³ (18.4 km/s vesc) |
| Insolation Flux | 21.9830 S⊕ (~29,919 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2529.900 LY (775.679 pc) |