Kepler-221 c
Astrophysical Synthesis & Habitability Characterization
Kepler-221 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-221, located approximately 1256.5 light-years (385.23 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1071% across the stellar disk), this world measures 2.93 Earth radii and has a measured mass of 9.3 Earth masses. Combining its mass and radius yields a mean bulk density of 2.04 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 19.9 km/s.
In its orbital architecture around Kepler-221, Kepler-221 c completes one full revolution every 5.691 Earth days at a semi-major axis of 0.059 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 112.8 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 860 K (+587°C / +1089°F) and receiving 119.84 S⊕ (~163,097 W/m²), Kepler-221 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-221 is classified as a stellar host with an effective photospheric temperature of 5,243 K, a radius of 0.821 R☉, a mass of 0.854 M☉, an estimated bolometric luminosity of 0.457 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.78 Gyr and a metallicity of [Fe/H] = 0.062 dex (metal-rich relative to the Sun). From Earth, Kepler-221 shines at apparent V-band magnitude 13.97 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-221 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-221 c sharing its stellar neighborhood alongside Kepler-221 b, Kepler-221 d, Kepler-221 e.
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-221 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,243 K |
| Stellar Radius | 0.8210 R☉ |
| Stellar Mass | 0.8540 M☉ |
| Bolometric Luminosity | 0.457 L☉ |
| Metallicity [Fe/H] | 0.062 dex |
| Stellar Age | 1.780 Gyr |
| Apparent Magnitude | V: 13.970 · G: 13.749 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.059000 AU |
| Orbital Period | 5.691 days |
| Mean Orbital Velocity | 112.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.7600° |
| Mean Bulk Density | 2.04 g/cm³ (19.9 km/s vesc) |
| Insolation Flux | 119.8360 S⊕ (~163,097 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1256.500 LY (385.231 pc) |