Kepler-408 b

Astrophysical Synthesis & Habitability Characterization

Kepler-408 b is a confirmed terrestrial exoplanet orbiting the star Kepler-408, located approximately 289.6 light-years (88.78 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0037% across the stellar disk), this world measures 0.82 Earth radii and has a measured mass of 5 Earth masses. Combining its mass and radius yields a mean bulk density of 50 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 7.44 g⊕ (72.96 m/s²), and an escape velocity of 27.6 km/s.

In its orbital architecture around Kepler-408, Kepler-408 b completes one full revolution every 2.465 Earth days at a semi-major axis of 0.03592 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 158.5 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 1561 K (+1288°C / +2350°F) and receiving 1,503.58 S⊕ (~2,046,374 W/m²), Kepler-408 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-408 is classified as a stellar host with an effective photospheric temperature of 6,104 K, a radius of 1.23 R☉, a mass of 1.08 M☉, an estimated bolometric luminosity of 1.884 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.68 Gyr and a metallicity of [Fe/H] = -0.2 dex (metal-poor relative to the Sun). From Earth, Kepler-408 shines at apparent V-band magnitude 8.834 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere.

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