Kepler-558 b

Astrophysical Synthesis & Habitability Characterization

Kepler-558 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-558, located approximately 2158.7 light-years (661.88 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.072% across the stellar disk), this world measures 2.37 Earth radii and has a measured mass of 6.21 Earth masses. Combining its mass and radius yields a mean bulk density of 2.57 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.11 g⊕ (10.89 m/s²), and an escape velocity of 18.1 km/s.

In its orbital architecture around Kepler-558, Kepler-558 b completes one full revolution every 29.008 Earth days at a semi-major axis of 0.1759 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 66 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 498 K (+225°C / +437°F) and receiving 15.23 S⊕ (~20,724 W/m²), Kepler-558 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-558 is classified as a stellar host with an effective photospheric temperature of 5,242 K, a radius of 0.81 R☉, a mass of 0.85 M☉, an estimated bolometric luminosity of 0.444 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.47 Gyr and a metallicity of [Fe/H] = -0.06 dex (near-solar heavy-element abundance). From Earth, Kepler-558 shines at apparent V-band magnitude 14.899 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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