Kepler-631 b

Astrophysical Synthesis & Habitability Characterization

Kepler-631 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-631, located approximately 2485.2 light-years (761.97 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.04% across the stellar disk), this world measures 2.9 Earth radii and has a measured mass of 8.75 Earth masses. Combining its mass and radius yields a mean bulk density of 1.98 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.4 km/s.

In its orbital architecture around Kepler-631, Kepler-631 b completes one full revolution every 17.98 Earth days at a semi-major axis of 0.14017 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 84.8 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 828 K (+555°C / +1031°F) and receiving 94.14 S⊕ (~128,120 W/m²), Kepler-631 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-631 is classified as a stellar host with an effective photospheric temperature of 6,185 K, a radius of 1.33 R☉, a mass of 1.24 M☉, an estimated bolometric luminosity of 2.322 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.51 Gyr and a metallicity of [Fe/H] = 0.23 dex (metal-rich relative to the Sun). From Earth, Kepler-631 shines at apparent V-band magnitude 13.563 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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