Kepler-261 c
Astrophysical Synthesis & Habitability Characterization
Kepler-261 c is a confirmed super-earth exoplanet orbiting the star Kepler-261, located approximately 1035.5 light-years (317.5 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0533% across the stellar disk), this world measures 2 Earth radii and has a measured mass of 4.66 Earth masses. Combining its mass and radius yields a mean bulk density of 3.21 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.17 g⊕ (11.47 m/s²), and an escape velocity of 17.1 km/s.
In its orbital architecture around Kepler-261, Kepler-261 c completes one full revolution every 24.571 Earth days at a semi-major axis of 0.156 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 69.1 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 505 K (+232°C / +450°F) and receiving 14.51 S⊕ (~19,751 W/m²), Kepler-261 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-261 is classified as a stellar host with an effective photospheric temperature of 5,098 K, a radius of 0.794 R☉, a mass of 0.834 M☉, an estimated bolometric luminosity of 0.382 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.87 Gyr and a metallicity of [Fe/H] = 0.162 dex (metal-rich relative to the Sun). From Earth, Kepler-261 shines at apparent V-band magnitude 13.738 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-261 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-261 c sharing its stellar neighborhood alongside Kepler-261 b.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-261 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,098 K |
| Stellar Radius | 0.7940 R☉ |
| Stellar Mass | 0.8340 M☉ |
| Bolometric Luminosity | 0.382 L☉ |
| Metallicity [Fe/H] | 0.162 dex |
| Stellar Age | 0.870 Gyr |
| Apparent Magnitude | V: 13.738 · G: 13.529 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.156000 AU |
| Orbital Period | 24.571 days |
| Mean Orbital Velocity | 69.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.5200° |
| Mean Bulk Density | 3.21 g/cm³ (17.1 km/s vesc) |
| Insolation Flux | 14.5120 S⊕ (~19,751 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1035.500 LY (317.499 pc) |