Kepler-638 b

Astrophysical Synthesis & Habitability Characterization

Kepler-638 b is a confirmed super-earth exoplanet orbiting the star Kepler-638, located approximately 3232.9 light-years (991.21 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0325% across the stellar disk), this world measures 1.83 Earth radii and has a measured mass of 4.01 Earth masses. Combining its mass and radius yields a mean bulk density of 3.61 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.2 g⊕ (11.77 m/s²), and an escape velocity of 16.6 km/s.

In its orbital architecture around Kepler-638, Kepler-638 b completes one full revolution every 6.08 Earth days at a semi-major axis of 0.06695 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 119.8 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 1111 K (+838°C / +1540°F) and receiving 872.57 S⊕ (~1,187,564 W/m²), Kepler-638 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-638 is classified as a stellar host with an effective photospheric temperature of 5,382 K, a radius of 0.93 R☉, a mass of 0.88 M☉, an estimated bolometric luminosity of 0.651 L☉. Stellar evolution modeling indicates an estimated stellar age of 11.75 Gyr and a metallicity of [Fe/H] = 0.04 dex (near-solar heavy-element abundance). From Earth, Kepler-638 shines at apparent V-band magnitude 13.658 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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