K2-308 b
Astrophysical Synthesis & Habitability Characterization
K2-308 b is a confirmed gas giant exoplanet orbiting the star K2-308, located approximately 4287.4 light-years (1314.53 parsecs) from the Solar System. First announced in 2019 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.5375% across the stellar disk), this world measures 9.916 Earth radii (0.88 Jupiter radii) and has a measured mass of 70.6 Earth masses (0.22 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.4 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.72 g⊕ (7.06 m/s²), and an escape velocity of 29.8 km/s.
In its orbital architecture around K2-308, K2-308 b completes one full revolution every 3.386 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1214 K (+941°C / +1726°F) and receiving 512.92 S⊕ (~698,089 W/m²), K2-308 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-308 is classified as a stellar host with an effective photospheric temperature of 6,100 K, a radius of 1.24 R☉, a mass of 1.09 M☉, an estimated bolometric luminosity of 1.91 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.1 dex (near-solar heavy-element abundance). From Earth, K2-308 shines at apparent V-band magnitude 15.072 (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 | K2-308 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,100 K |
| Stellar Radius | 1.2400 R☉ |
| Stellar Mass | 1.0900 M☉ |
| Bolometric Luminosity | 1.91 L☉ |
| Metallicity [Fe/H] | -0.100 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 15.072 · G: 14.895 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 3.386 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.4400° |
| Mean Bulk Density | 0.4 g/cm³ (29.8 km/s vesc) |
| Insolation Flux | 512.9234 S⊕ (~698,089 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4287.400 LY (1314.530 pc) |