Kepler-781 b

Astrophysical Synthesis & Habitability Characterization

Kepler-781 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-781, located approximately 3471.8 light-years (1064.47 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1154% across the stellar disk), this world measures 2.89 Earth radii and has a measured mass of 8.7 Earth masses. Combining its mass and radius yields a mean bulk density of 1.99 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-781, Kepler-781 b completes one full revolution every 13.214 Earth days at a semi-major axis of 0.1019 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 83.9 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 629 K (+356°C / +673°F) and receiving 44.40 S⊕ (~60,424 W/m²), Kepler-781 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-781 is classified as a stellar host with an effective photospheric temperature of 5,162 K, a radius of 0.78 R☉, a mass of 0.81 M☉, an estimated bolometric luminosity of 0.388 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.9 Gyr and a metallicity of [Fe/H] = -0.1 dex (near-solar heavy-element abundance). From Earth, Kepler-781 shines at apparent V-band magnitude 16.207 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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