Kepler-108 b
Astrophysical Synthesis & Habitability Characterization
Kepler-108 b is a confirmed gas giant exoplanet orbiting the star Kepler-108, located approximately 1104.8 light-years (338.73 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1309% across the stellar disk), this world measures 8.65 Earth radii (0.77 Jupiter radii) and has a measured mass of 56 Earth masses (0.18 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.48 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.75 g⊕ (7.35 m/s²), and an escape velocity of 28.5 km/s.
In its orbital architecture around Kepler-108, Kepler-108 b completes one full revolution every 49.184 Earth days at a semi-major axis of 0.292 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 64.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.22 carries the world between 0.2278 AU at periapsis and 0.3562 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 669 K (+396°C / +745°F) and receiving 47.40 S⊕ (~64,511 W/m²), Kepler-108 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-108 is classified as a stellar host with an effective photospheric temperature of 5,854 K, a radius of 2.192 R☉, a mass of 1.247 M☉, an estimated bolometric luminosity of 5.063 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.89 Gyr and a metallicity of [Fe/H] = 0.326 dex (metal-rich relative to the Sun). From Earth, Kepler-108 shines at apparent V-band magnitude 12.657 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-108 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-108 b sharing its stellar neighborhood alongside Kepler-108 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-108 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,854 K |
| Stellar Radius | 2.1920 R☉ |
| Stellar Mass | 1.2470 M☉ |
| Bolometric Luminosity | 5.063 L☉ |
| Metallicity [Fe/H] | 0.326 dex |
| Stellar Age | 3.890 Gyr |
| Apparent Magnitude | V: 12.657 · G: 13.084 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.292000 AU |
| Orbital Period | 49.184 days |
| Mean Orbital Velocity | 64.6 km/s |
| Orbital Eccentricity (e) | 0.22000 |
| Orbital Inclination (i) | 89.9400° |
| Mean Bulk Density | 0.48 g/cm³ (28.5 km/s vesc) |
| Insolation Flux | 47.4000 S⊕ (~64,511 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1104.800 LY (338.732 pc) |