Kepler-978 b

Astrophysical Synthesis & Habitability Characterization

Kepler-978 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-978, located approximately 2226.1 light-years (682.52 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0632% across the stellar disk), this world measures 2.99 Earth radii and has a measured mass of 9.22 Earth masses. Combining its mass and radius yields a mean bulk density of 1.9 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.03 g⊕ (10.1 m/s²), and an escape velocity of 19.6 km/s.

In its orbital architecture around Kepler-978, Kepler-978 b completes one full revolution every 49.622 Earth days at a semi-major axis of 0.2726 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 59.8 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 546 K (+273°C / +523°F) and receiving 20.99 S⊕ (~28,567 W/m²), Kepler-978 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-978 is classified as a stellar host with an effective photospheric temperature of 6,002 K, a radius of 1.09 R☉, a mass of 1.07 M☉, an estimated bolometric luminosity of 1.383 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.63 Gyr and a metallicity of [Fe/H] = -0.01 dex (near-solar heavy-element abundance). From Earth, Kepler-978 shines at apparent V-band magnitude 13.513 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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