Kepler-1981 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1981 b is a confirmed gas giant exoplanet orbiting the star Kepler-1981, located approximately 2150.7 light-years (659.4 parsecs) from the Solar System. First announced in 2023 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0792% across the stellar disk), this world measures 9.23 Earth radii (0.82 Jupiter radii) and has a measured mass of 62.5 Earth masses (0.2 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.44 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.73 g⊕ (7.16 m/s²), and an escape velocity of 29.1 km/s.

In its orbital architecture around Kepler-1981, Kepler-1981 b completes one full revolution every 453.542 Earth days (1.24Julian years) at a semi-major axis of 1.3292 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 31.9 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 390 K (+117°C / +243°F) and receiving 5.45 S⊕ (~7,417 W/m²), Kepler-1981 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-1981 is classified as a stellar host with an effective photospheric temperature of 5,874 K, a radius of 3.006 R☉, a mass of 1.519 M☉, an estimated bolometric luminosity of 9.652 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.12 dex (metal-rich relative to the Sun). From Earth, Kepler-1981 shines at apparent V-band magnitude 13.563 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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