K2-105 b

Astrophysical Synthesis & Habitability Characterization

K2-105 b is a confirmed sub-neptune exoplanet orbiting the star K2-105, located approximately 645.8 light-years (197.99 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1186% across the stellar disk), this world measures 3.4 Earth radii (0.3 Jupiter radii) and has a measured mass of 15.4 Earth 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 1.33 g⊕ (13.04 m/s²), and an escape velocity of 23.8 km/s.

In its orbital architecture around K2-105, K2-105 b completes one full revolution every 8.267 Earth days at a semi-major axis of 0.0796 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 104.7 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 805 K (+532°C / +990°F) and receiving 100.00 S⊕ (~136,100 W/m²), K2-105 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star K2-105 is classified as an orange K-type star of spectral type K1 with an effective photospheric temperature of 5,373 K, a radius of 0.905 R☉, a mass of 0.94 M☉, an estimated bolometric luminosity of 0.612 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.6 Gyr and a metallicity of [Fe/H] = 0.22 dex (metal-rich relative to the Sun). From Earth, K2-105 shines at apparent V-band magnitude 11.752 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

Discovery Facility: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).