Kepler-308 c
Astrophysical Synthesis & Habitability Characterization
Kepler-308 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-308, located approximately 4357.2 light-years (1335.92 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0443% across the stellar disk), this world measures 2.16 Earth radii and has a measured mass of 5.31 Earth masses. Combining its mass and radius yields a mean bulk density of 2.91 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.14 g⊕ (11.18 m/s²), and an escape velocity of 17.5 km/s.
In its orbital architecture around Kepler-308, Kepler-308 c completes one full revolution every 15.382 Earth days at a semi-major axis of 0.123 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 87 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 714 K (+441°C / +826°F) and receiving 58.68 S⊕ (~79,862 W/m²), Kepler-308 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-308 is classified as a stellar host with an effective photospheric temperature of 5,895 K, a radius of 0.941 R☉, a mass of 0.92 M☉, an estimated bolometric luminosity of 0.959 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.5 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, Kepler-308 shines at apparent V-band magnitude 16.019 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-308 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-308 c sharing its stellar neighborhood alongside Kepler-308 b.
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-308 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,895 K |
| Stellar Radius | 0.9410 R☉ |
| Stellar Mass | 0.9200 M☉ |
| Bolometric Luminosity | 0.959 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 0.500 Gyr |
| Apparent Magnitude | V: 16.019 · G: 15.851 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.123000 AU |
| Orbital Period | 15.382 days |
| Mean Orbital Velocity | 87 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9700° |
| Mean Bulk Density | 2.91 g/cm³ (17.5 km/s vesc) |
| Insolation Flux | 58.6790 S⊕ (~79,862 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4357.200 LY (1335.920 pc) |