Kepler-991 b

Astrophysical Synthesis & Habitability Characterization

Kepler-991 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-991, located approximately 1270.6 light-years (389.56 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1457% across the stellar disk), this world measures 2.54 Earth radii and has a measured mass of 6.99 Earth masses. Combining its mass and radius yields a mean bulk density of 2.35 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 18.6 km/s.

In its orbital architecture around Kepler-991, Kepler-991 b completes one full revolution every 82.534 Earth days at a semi-major axis of 0.3104 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 40.9 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.

☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.540 R⊕, Kepler-991 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.

The host star Kepler-991 is classified as a stellar host with an effective photospheric temperature of 4,392 K, a radius of 0.61 R☉, a mass of 0.64 M☉, an estimated bolometric luminosity of 0.124 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.47 Gyr and a metallicity of [Fe/H] = -0.25 dex (metal-poor relative to the Sun). From Earth, Kepler-991 shines at apparent V-band magnitude 15.626 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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