K2-222 b

Astrophysical Synthesis & Habitability Characterization

K2-222 b is a confirmed sub-neptune exoplanet orbiting the star K2-222, located approximately 330.5 light-years (101.32 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0379% across the stellar disk), this world measures 2.275 Earth radii and has a measured mass of 7.5 Earth masses. Combining its mass and radius yields a mean bulk density of 3.51 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.45 g⊕ (14.22 m/s²), and an escape velocity of 20.3 km/s.

In its orbital architecture around K2-222, K2-222 b completes one full revolution every 15.389 Earth days at a semi-major axis of 0.1186 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). With a near-circular eccentricity of e = 0.021 (ranging from 0.1161 AU at periapsis to 0.1211 AU at apoapsis), the planet experiences minimal orbital distance variation.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 803 K (+530°C / +986°F) and receiving 95.00 S⊕ (~129,295 W/m²), K2-222 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star K2-222 is classified as a solar-type yellow star of spectral type G0 with an effective photospheric temperature of 5,942 K, a radius of 1.072 R☉, a mass of 0.94 M☉, an estimated bolometric luminosity of 1.285 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.1 Gyr and a metallicity of [Fe/H] = -0.315 dex (metal-poor relative to the Sun). From Earth, K2-222 shines at apparent V-band magnitude 9.543 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere.

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