K2-225 b

Astrophysical Synthesis & Habitability Characterization

K2-225 b is a confirmed sub-neptune exoplanet orbiting the star K2-225, located approximately 1166.9 light-years (357.78 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 3.609 Earth radii (0.32 Jupiter radii) and has a measured mass of 12.7 Earth masses. Combining its mass and radius yields a mean bulk density of 1.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 21 km/s.

In its orbital architecture around K2-225, K2-225 b completes one full revolution every 15.872 Earth days at a semi-major axis of 0.1409 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 96.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.23 carries the world between 0.1085 AU at periapsis and 0.1733 AU at apoapsis, driving measurable seasonal insolation cycles.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 923 K (+650°C / +1202°F) and receiving 121.39 S⊕ (~165,216 W/m²), K2-225 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star K2-225 is classified as a stellar host with an effective photospheric temperature of 5,520 K, a radius of 1.7 R☉, a mass of 1.482 M☉, an estimated bolometric luminosity of 2.407 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.012 Gyr and a metallicity of [Fe/H] = 0.486 dex (metal-rich relative to the Sun). From Earth, K2-225 shines at apparent V-band magnitude 11.836 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.

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