Kepler-218 c
Astrophysical Synthesis & Habitability Characterization
Kepler-218 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-218, located approximately 2140.8 light-years (656.38 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0733% across the stellar disk), this world measures 3.14 Earth radii (0.28 Jupiter radii) and has a measured mass of 10 Earth masses. Combining its mass and radius yields a mean bulk density of 1.78 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.01 g⊕ (9.9 m/s²), and an escape velocity of 20 km/s.
In its orbital architecture around Kepler-218, Kepler-218 c completes one full revolution every 44.7 Earth days at a semi-major axis of 0.248 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 60.4 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.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 500 K (+227°C / +441°F) and receiving 16.15 S⊕ (~21,976 W/m²), Kepler-218 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-218 is classified as a stellar host with an effective photospheric temperature of 5,502 K, a radius of 1.063 R☉, a mass of 1.019 M☉, an estimated bolometric luminosity of 0.929 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.02 Gyr and a metallicity of [Fe/H] = 0.37 dex (metal-rich relative to the Sun). From Earth, Kepler-218 shines at apparent V-band magnitude 14.035 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-218 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-218 c sharing its stellar neighborhood alongside Kepler-218 b, Kepler-218 d.
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-218 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,502 K |
| Stellar Radius | 1.0630 R☉ |
| Stellar Mass | 1.0190 M☉ |
| Bolometric Luminosity | 0.929 L☉ |
| Metallicity [Fe/H] | 0.370 dex |
| Stellar Age | 3.020 Gyr |
| Apparent Magnitude | V: 14.035 · G: 13.907 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.248000 AU |
| Orbital Period | 44.7 days |
| Mean Orbital Velocity | 60.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.4600° |
| Mean Bulk Density | 1.78 g/cm³ (20 km/s vesc) |
| Insolation Flux | 16.1470 S⊕ (~21,976 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2140.800 LY (656.380 pc) |