K2-108 b
Astrophysical Synthesis & Habitability Characterization
K2-108 b is a confirmed sub-neptune exoplanet orbiting the star K2-108, located approximately 1556.7 light-years (477.3 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0771% across the stellar disk), this world measures 5.33 Earth radii (0.48 Jupiter radii) and has a measured mass of 59.4 Earth masses (0.19 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.16 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 2.09 g⊕ (20.5 m/s²), and an escape velocity of 37.3 km/s.
In its orbital architecture around K2-108, K2-108 b completes one full revolution every 4.734 Earth days at a semi-major axis of 0.0581 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 133.5 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.18 carries the world between 0.0476 AU at periapsis and 0.0686 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1360 K (+1087°C / +1989°F) and receiving 762.00 S⊕ (~1,037,082 W/m²), K2-108 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-108 is classified as a stellar host with an effective photospheric temperature of 5,599 K, a radius of 1.76 R☉, a mass of 1.17 M☉, an estimated bolometric luminosity of 2.731 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.8 Gyr and a metallicity of [Fe/H] = 0.36 dex (metal-rich relative to the Sun). From Earth, K2-108 shines at apparent V-band magnitude 12.339 (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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-108 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,599 K |
| Stellar Radius | 1.7600 R☉ |
| Stellar Mass | 1.1700 M☉ |
| Bolometric Luminosity | 2.731 L☉ |
| Metallicity [Fe/H] | 0.360 dex |
| Stellar Age | 7.800 Gyr |
| Apparent Magnitude | V: 12.339 · G: 12.170 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.058100 AU |
| Orbital Period | 4.734 days |
| Mean Orbital Velocity | 133.5 km/s |
| Orbital Eccentricity (e) | 0.18000 |
| Orbital Inclination (i) | 86.1351° |
| Mean Bulk Density | 2.16 g/cm³ (37.3 km/s vesc) |
| Insolation Flux | 762.0000 S⊕ (~1,037,082 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1556.700 LY (477.295 pc) |