Kepler-639 b

Astrophysical Synthesis & Habitability Characterization

Kepler-639 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-639, located approximately 2773.1 light-years (850.24 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0286% across the stellar disk), this world measures 2.38 Earth radii and has a measured mass of 6.26 Earth masses. Combining its mass and radius yields a mean bulk density of 2.56 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.11 g⊕ (10.89 m/s²), and an escape velocity of 18.1 km/s.

In its orbital architecture around Kepler-639, Kepler-639 b completes one full revolution every 10.214 Earth days at a semi-major axis of 0.09358 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 99.7 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 957 K (+684°C / +1263°F) and receiving 295.83 S⊕ (~402,619 W/m²), Kepler-639 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-639 is classified as a stellar host with an effective photospheric temperature of 5,896 K, a radius of 1.29 R☉, a mass of 1.14 M☉, an estimated bolometric luminosity of 1.804 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.37 Gyr and a metallicity of [Fe/H] = 0.23 dex (metal-rich relative to the Sun). From Earth, Kepler-639 shines at apparent V-band magnitude 13.358 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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