Kepler-1731 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1731 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1731, located approximately 554.3 light-years (169.95 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1395% across the stellar disk), this world measures 2.933 Earth radii and has a measured mass of 8.92 Earth masses. Combining its mass and radius yields a mean bulk density of 1.95 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 19.5 km/s.

In its orbital architecture around Kepler-1731, Kepler-1731 b completes one full revolution every 21.761 Earth days at a semi-major axis of 0.1399 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 69.9 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 486 K (+213°C / +415°F) and receiving 13.30 S⊕ (~18,101 W/m²), Kepler-1731 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-1731 is classified as a stellar host with an effective photospheric temperature of 4,859 K, a radius of 0.72 R☉, a mass of 0.781 M☉, an estimated bolometric luminosity of 0.259 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.14 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, Kepler-1731 shines at apparent V-band magnitude 12.742 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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