Kepler-18 b
Astrophysical Synthesis & Habitability Characterization
Kepler-18 b is a confirmed super-earth exoplanet orbiting the star Kepler-18, located approximately 1412.4 light-years (433.05 parsecs) from the Solar System. First announced in 2011 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0274% across the stellar disk), this world measures 2 Earth radii and has a measured mass of 6.9 Earth masses. Combining its mass and radius yields a mean bulk density of 4.76 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.73 g⊕ (16.97 m/s²), and an escape velocity of 20.8 km/s.
In its orbital architecture around Kepler-18, Kepler-18 b completes one full revolution every 3.505 Earth days at a semi-major axis of 0.0447 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 138.8 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 1165 K (+892°C / +1638°F) and receiving 355.74 S⊕ (~484,155 W/m²), Kepler-18 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-18 is classified as a stellar host with an effective photospheric temperature of 5,345 K, a radius of 1.108 R☉, a mass of 0.972 M☉, an estimated bolometric luminosity of 0.899 L☉. Stellar evolution modeling indicates an estimated stellar age of 10 Gyr and a metallicity of [Fe/H] = 0.19 dex (metal-rich relative to the Sun). From Earth, Kepler-18 shines at apparent V-band magnitude 13.771 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-18 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-18 b sharing its stellar neighborhood alongside Kepler-18 c, Kepler-18 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-18 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,345 K |
| Stellar Radius | 1.1080 R☉ |
| Stellar Mass | 0.9720 M☉ |
| Bolometric Luminosity | 0.899 L☉ |
| Metallicity [Fe/H] | 0.190 dex |
| Stellar Age | 10.000 Gyr |
| Apparent Magnitude | V: 13.771 · G: 13.539 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.044700 AU |
| Orbital Period | 3.505 days |
| Mean Orbital Velocity | 138.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 84.9200° |
| Mean Bulk Density | 4.76 g/cm³ (20.8 km/s vesc) |
| Insolation Flux | 355.7350 S⊕ (~484,155 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1412.400 LY (433.047 pc) |