Kepler-1684 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1684 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1684, located approximately 2028.7 light-years (622 parsecs) from the Solar System. First announced in 2020 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1558% across the stellar disk), this world measures 2.871 Earth radii and has a measured mass of 8.6 Earth masses. Combining its mass and radius yields a mean bulk density of 2 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.4 km/s.

In its orbital architecture around Kepler-1684, Kepler-1684 b completes one full revolution every 47.706 Earth days at a semi-major axis of 0.2253 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 51.4 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.

☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.871 R⊕, Kepler-1684 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.

The host star Kepler-1684 is classified as a stellar host with an effective photospheric temperature of 4,707 K, a radius of 0.6668 R☉, a mass of 0.75 M☉, an estimated bolometric luminosity of 0.196 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.127 dex (metal-rich relative to the Sun). From Earth, Kepler-1684 shines at apparent V-band magnitude 15.951 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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