Kepler-521 b

Astrophysical Synthesis & Habitability Characterization

Kepler-521 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-521, located approximately 2709.2 light-years (830.64 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0399% across the stellar disk), this world measures 3.18 Earth radii (0.28 Jupiter radii) and has a measured mass of 10.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.75 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.01 g⊕ (9.9 m/s²), and an escape velocity of 20 km/s.

In its orbital architecture around Kepler-521, Kepler-521 b completes one full revolution every 22.208 Earth days at a semi-major axis of 0.17116 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). 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 803 K (+530°C / +986°F) and receiving 160.61 S⊕ (~218,593 W/m²), Kepler-521 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-521 is classified as a stellar host with an effective photospheric temperature of 6,406 K, a radius of 1.46 R☉, a mass of 1.34 M☉, an estimated bolometric luminosity of 3.221 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.78 Gyr and a metallicity of [Fe/H] = 0.25 dex (metal-rich relative to the Sun). From Earth, Kepler-521 shines at apparent V-band magnitude 12.94 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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