Kepler-1538 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1538 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1538, located approximately 3670.2 light-years (1125.3 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.063% across the stellar disk), this world measures 2.82 Earth radii and has a measured mass of 8.35 Earth masses. Combining its mass and radius yields a mean bulk density of 2.05 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 19.2 km/s.

In its orbital architecture around Kepler-1538, Kepler-1538 b completes one full revolution every 175.139 Earth days at a semi-major axis of 0.6095 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 37.9 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 2.820 R⊕, Kepler-1538 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-1538 is classified as a stellar host with an effective photospheric temperature of 5,837 K, a radius of 1.03 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.105 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.37 Gyr and a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, Kepler-1538 shines at apparent V-band magnitude 15.551 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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