K2-77 b

Astrophysical Synthesis & Habitability Characterization

K2-77 b is a confirmed sub-neptune exoplanet orbiting the star K2-77, located approximately 462.3 light-years (141.73 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0837% across the stellar disk), this world measures 2.5 Earth radii and has a measured mass of 603.877 Earth masses (1.9 Jupiter masses). Combining its mass and radius yields a mean bulk density of 213.11 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 96.62 g⊕ (947.52 m/s²), and an escape velocity of 173.9 km/s.

In its orbital architecture around K2-77, K2-77 b completes one full revolution every 8.2 Earth days at a semi-major axis of 0.0753 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 99.9 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.29, swinging from 0.0535 AU at periapsis out to 0.0971 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 806 K (+533°C / +991°F) and receiving 58.00 S⊕ (~78,938 W/m²), K2-77 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star K2-77 is classified as a stellar host with an effective photospheric temperature of 5,160 K, a radius of 0.792 R☉, a mass of 0.847 M☉, an estimated bolometric luminosity of 0.399 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.7 Gyr and a metallicity of [Fe/H] = 0.13 dex (metal-rich relative to the Sun). From Earth, K2-77 shines at apparent V-band magnitude 12.224 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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