Kepler-1261 b

Astrophysical Synthesis & Habitability Characterization

Kepler-1261 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1261, located approximately 2427.6 light-years (744.29 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0724% across the stellar disk), this world measures 2.26 Earth radii and has a measured mass of 5.73 Earth masses. Combining its mass and radius yields a mean bulk density of 2.74 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.8 km/s.

In its orbital architecture around Kepler-1261, Kepler-1261 b completes one full revolution every 48.431 Earth days at a semi-major axis of 0.239 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 53.7 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 396 K (+123°C / +253°F) and receiving 4.74 S⊕ (~6,457 W/m²), Kepler-1261 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star Kepler-1261 is classified as a stellar host with an effective photospheric temperature of 5,006 K, a radius of 0.77 R☉, a mass of 0.82 M☉, an estimated bolometric luminosity of 0.334 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.47 Gyr and a metallicity of [Fe/H] = 0.03 dex (near-solar heavy-element abundance). From Earth, Kepler-1261 shines at apparent V-band magnitude 15.817 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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