Kepler-1866 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1866 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1866, located approximately 3185.7 light-years (976.74 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0311% across the stellar disk), this world measures 2.082 Earth radii and has a measured mass of 4.99 Earth masses. Combining its mass and radius yields a mean bulk density of 3.05 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.15 g⊕ (11.28 m/s²), and an escape velocity of 17.3 km/s.

In its orbital architecture around Kepler-1866, Kepler-1866 b completes one full revolution every 11.66 Earth days at a semi-major axis of 0.1016 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 94.8 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 834 K (+561°C / +1042°F) and receiving 114.36 S⊕ (~155,644 W/m²), Kepler-1866 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-1866 is classified as a stellar host with an effective photospheric temperature of 5,791 K, a radius of 1.083 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.183 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.3 Gyr and a metallicity of [Fe/H] = 0.16 dex (metal-rich relative to the Sun). From Earth, Kepler-1866 shines at apparent V-band magnitude 14.418 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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