K2-27 b
Astrophysical Synthesis & Habitability Characterization
K2-27 b is a confirmed sub-neptune exoplanet orbiting the star K2-27, located approximately 814.2 light-years (249.65 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.2461% across the stellar disk), this world measures 4.74 Earth radii (0.42 Jupiter radii) and has a measured mass of 30.2 Earth masses (0.1 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.56 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.34 g⊕ (13.14 m/s²), and an escape velocity of 28.2 km/s.
In its orbital architecture around K2-27, K2-27 b completes one full revolution every 6.771 Earth days at a semi-major axis of 0.06702 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 107.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.251, swinging from 0.0502 AU at periapsis out to 0.0838 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 836 K (+563°C / +1045°F) and receiving 116.00 S⊕ (~157,876 W/m²), K2-27 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-27 is classified as a stellar host with an effective photospheric temperature of 5,246 K, a radius of 0.876 R☉, a mass of 0.88 M☉, an estimated bolometric luminosity of 0.521 L☉. Stellar evolution modeling indicates an estimated stellar age of 10.3 Gyr and a metallicity of [Fe/H] = 0.12 dex (metal-rich relative to the Sun). From Earth, K2-27 shines at apparent V-band magnitude 12.689 (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 | K2-27 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,246 K |
| Stellar Radius | 0.8760 R☉ |
| Stellar Mass | 0.8800 M☉ |
| Bolometric Luminosity | 0.521 L☉ |
| Metallicity [Fe/H] | 0.120 dex |
| Stellar Age | 10.300 Gyr |
| Apparent Magnitude | V: 12.689 · G: 12.453 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.067020 AU |
| Orbital Period | 6.771 days |
| Mean Orbital Velocity | 107.7 km/s |
| Orbital Eccentricity (e) | 0.25100 |
| Orbital Inclination (i) | 88.8713° |
| Mean Bulk Density | 1.56 g/cm³ (28.2 km/s vesc) |
| Insolation Flux | 116.0000 S⊕ (~157,876 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 814.200 LY (249.645 pc) |