Kepler-657 b

Astrophysical Synthesis & Habitability Characterization

Kepler-657 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-657, located approximately 5518.2 light-years (1691.88 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1021% across the stellar disk), this world measures 3.52 Earth radii (0.31 Jupiter radii) and has a measured mass of 12.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.54 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 20.8 km/s.

In its orbital architecture around Kepler-657, Kepler-657 b completes one full revolution every 24.544 Earth days at a semi-major axis of 0.17337 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76.8 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 616 K (+343°C / +649°F) and receiving 62.20 S⊕ (~84,654 W/m²), Kepler-657 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-657 is classified as a stellar host with an effective photospheric temperature of 5,808 K, a radius of 1.01 R☉, a mass of 1.01 M☉, an estimated bolometric luminosity of 1.041 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.17 Gyr and a metallicity of [Fe/H] = 0.03 dex (near-solar heavy-element abundance). From Earth, Kepler-657 shines at apparent V-band magnitude 15.404 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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