Kepler-1308 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1308 b is a confirmed sub-earth exoplanet orbiting the star Kepler-1308, located approximately 367.6 light-years (112.71 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0197% across the stellar disk), this world measures 0.52 Earth radii and has a measured mass of 0.093 Earth masses. Combining its mass and radius yields a mean bulk density of 3.65 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 0.34 g⊕ (3.33 m/s²), and an escape velocity of 4.7 km/s.
In its orbital architecture around Kepler-1308, Kepler-1308 b completes one full revolution every 2.104 Earth days at a semi-major axis of 0.025 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 129.2 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 662 K (+389°C / +732°F) and receiving 58.11 S⊕ (~79,085 W/m²), Kepler-1308 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1308 is classified as a stellar host with an effective photospheric temperature of 3,468 K, a radius of 0.34 R☉, a mass of 0.35 M☉, an estimated bolometric luminosity of 0.015 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.72 Gyr and a metallicity of [Fe/H] = -0.13 dex (metal-poor relative to the Sun). From Earth, Kepler-1308 shines at apparent V-band magnitude 16.4 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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-1308 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 3,468 K |
| Stellar Radius | 0.3400 R☉ |
| Stellar Mass | 0.3500 M☉ |
| Bolometric Luminosity | 0.015 L☉ |
| Metallicity [Fe/H] | -0.130 dex |
| Stellar Age | 3.720 Gyr |
| Apparent Magnitude | V: 16.400 · G: 14.474 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.025000 AU |
| Orbital Period | 2.104 days |
| Mean Orbital Velocity | 129.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 83.3900° |
| Mean Bulk Density | 3.65 g/cm³ (4.7 km/s vesc) |
| Insolation Flux | 58.1080 S⊕ (~79,085 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 367.600 LY (112.705 pc) |