K2-15 b
Astrophysical Synthesis & Habitability Characterization
K2-15 b is a confirmed sub-neptune exoplanet orbiting the star K2-15, located approximately 1611.2 light-years (493.99 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1118% across the stellar disk), this world measures 2.48 Earth radii and has a measured mass of 6.71 Earth masses. Combining its mass and radius yields a mean bulk density of 2.43 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.4 km/s.
In its orbital architecture around K2-15, K2-15 b completes one full revolution every 11.81 Earth days at a semi-major axis of 0.091 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 83.8 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 676 K (+403°C / +757°F) and receiving 48.00 S⊕ (~65,328 W/m²), K2-15 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-15 is classified as a solar-type yellow star of spectral type G8 with an effective photospheric temperature of 5,131 K, a radius of 0.68 R☉, a mass of 0.72 M☉, an estimated bolometric luminosity of 0.288 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.46 dex (metal-poor relative to the Sun). From Earth, K2-15 shines at apparent V-band magnitude 14.758 (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 | K2-15 |
| Spectral Type | G8 |
| Effective Temp (Teff) | 5,131 K |
| Stellar Radius | 0.6800 R☉ |
| Stellar Mass | 0.7200 M☉ |
| Bolometric Luminosity | 0.288 L☉ |
| Metallicity [Fe/H] | -0.460 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 14.758 · G: 14.424 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.091000 AU |
| Orbital Period | 11.81 days |
| Mean Orbital Velocity | 83.8 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.43 g/cm³ (18.4 km/s vesc) |
| Insolation Flux | 48.0000 S⊕ (~65,328 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1611.200 LY (493.992 pc) |