Kepler-1204 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1204 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1204, located approximately 3833.1 light-years (1175.22 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0737% across the stellar disk), this world measures 3.05 Earth radii (0.27 Jupiter radii) and has a measured mass of 9.53 Earth masses. Combining its mass and radius yields a mean bulk density of 1.85 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 19.8 km/s.

In its orbital architecture around Kepler-1204, Kepler-1204 b completes one full revolution every 85.735 Earth days at a semi-major axis of 0.3877 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 49.2 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 448 K (+175°C / +347°F) and receiving 7.02 S⊕ (~9,556 W/m²), Kepler-1204 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-1204 is classified as a stellar host with an effective photospheric temperature of 5,825 K, a radius of 1.03 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.096 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.27 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, Kepler-1204 shines at apparent V-band magnitude 15.45 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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