Kepler-873 b

Astrophysical Synthesis & Habitability Characterization

Kepler-873 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-873, located approximately 3855.9 light-years (1182.22 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0733% across the stellar disk), this world measures 3.75 Earth radii (0.33 Jupiter radii) and has a measured mass of 13.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.41 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.96 g⊕ (9.41 m/s²), and an escape velocity of 21.2 km/s.

In its orbital architecture around Kepler-873, Kepler-873 b completes one full revolution every 20.553 Earth days at a semi-major axis of 0.1542 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 81.6 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 749 K (+476°C / +889°F) and receiving 68.02 S⊕ (~92,568 W/m²), Kepler-873 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-873 is classified as a stellar host with an effective photospheric temperature of 6,163 K, a radius of 1.27 R☉, a mass of 1.18 M☉, an estimated bolometric luminosity of 2.088 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.95 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, Kepler-873 shines at apparent V-band magnitude 15.052 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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