Kepler-1820 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1820 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1820, located approximately 4649 light-years (1425.39 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0943% across the stellar disk), this world measures 3.119 Earth radii (0.28 Jupiter radii) and has a measured mass of 9.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.8 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 19.9 km/s.

In its orbital architecture around Kepler-1820, Kepler-1820 b completes one full revolution every 31.032 Earth days at a semi-major axis of 0.1964 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 68.9 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 561 K (+288°C / +550°F) and receiving 23.41 S⊕ (~31,861 W/m²), Kepler-1820 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-1820 is classified as a stellar host with an effective photospheric temperature of 5,841 K, a radius of 0.931 R☉, a mass of 1.047 M☉, an estimated bolometric luminosity of 0.905 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.4 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, Kepler-1820 shines at apparent V-band magnitude 15.759 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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