K2-12 b
Astrophysical Synthesis & Habitability Characterization
K2-12 b is a confirmed sub-neptune exoplanet orbiting the star K2-12, located approximately 1064.5 light-years (326.38 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0401% across the stellar disk), this world measures 2.44 Earth radii and has a measured mass of 5.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.97 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.87 g⊕ (8.53 m/s²), and an escape velocity of 16.3 km/s.
In its orbital architecture around K2-12, K2-12 b completes one full revolution every 8.282 Earth days at a semi-major axis of 0.0792 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 104 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.5, swinging from 0.0396 AU at periapsis out to 0.1188 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1026 K (+753°C / +1387°F) and receiving 185.00 S⊕ (~251,785 W/m²), K2-12 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-12 is classified as a warm F-type star of spectral type F9 with an effective photospheric temperature of 5,672 K, a radius of 1.117 R☉, a mass of 0.965 M☉, an estimated bolometric luminosity of 1.159 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.9 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, K2-12 shines at apparent V-band magnitude 12.38 (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 | K2-12 |
| Spectral Type | F9 |
| Effective Temp (Teff) | 5,672 K |
| Stellar Radius | 1.1170 R☉ |
| Stellar Mass | 0.9650 M☉ |
| Bolometric Luminosity | 1.159 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 8.900 Gyr |
| Apparent Magnitude | V: 12.380 · G: 12.088 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.079200 AU |
| Orbital Period | 8.282 days |
| Mean Orbital Velocity | 104 km/s |
| Orbital Eccentricity (e) | 0.50000 |
| Orbital Inclination (i) | 87.6000° |
| Mean Bulk Density | 1.97 g/cm³ (16.3 km/s vesc) |
| Insolation Flux | 185.0000 S⊕ (~251,785 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1064.500 LY (326.381 pc) |