K2-33 b

Astrophysical Synthesis & Habitability Characterization

K2-33 b is a confirmed sub-neptune exoplanet orbiting the star K2-33, located approximately 454.2 light-years (139.27 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1937% across the stellar disk), this world measures 5.04 Earth radii (0.45 Jupiter radii) and has a measured mass of 1175.971 Earth masses (3.7 Jupiter masses). Combining its mass and radius yields a mean bulk density of 50.65 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 46.3 g⊕ (454.05 m/s²), and an escape velocity of 170.9 km/s.

In its orbital architecture around K2-33, K2-33 b completes one full revolution every 5.425 Earth days at a semi-major axis of 0.0409 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 82 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 850 K (+577°C / +1071°F) and receiving 89.67 S⊕ (~122,040 W/m²), K2-33 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star K2-33 is classified as a low-mass red dwarf of spectral type M3.3 with an effective photospheric temperature of 3,540 K, a radius of 1.05 R☉, a mass of 0.56 M☉, an estimated bolometric luminosity of 0.155 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.009 Gyr. From Earth, K2-33 shines at apparent V-band magnitude 15.838 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.

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