Kepler-818 b
Astrophysical Synthesis & Habitability Characterization
Kepler-818 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-818, located approximately 3017.1 light-years (925.04 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.2593% across the stellar disk), this world measures 5.11 Earth radii (0.46 Jupiter radii) and has a measured mass of 22.9 Earth masses. Combining its mass and radius yields a mean bulk density of 0.95 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.88 g⊕ (8.63 m/s²), and an escape velocity of 23.7 km/s.
In its orbital architecture around Kepler-818, Kepler-818 b completes one full revolution every 10.035 Earth days at a semi-major axis of 0.0886 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 96 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 786 K (+513°C / +955°F) and receiving 100.78 S⊕ (~137,160 W/m²), Kepler-818 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-818 is classified as a stellar host with an effective photospheric temperature of 5,638 K, a radius of 0.92 R☉, a mass of 0.94 M☉, an estimated bolometric luminosity of 0.767 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.98 Gyr and a metallicity of [Fe/H] = -0.08 dex (near-solar heavy-element abundance). From Earth, Kepler-818 shines at apparent V-band magnitude 15.368 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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-818 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,638 K |
| Stellar Radius | 0.9200 R☉ |
| Stellar Mass | 0.9400 M☉ |
| Bolometric Luminosity | 0.767 L☉ |
| Metallicity [Fe/H] | -0.080 dex |
| Stellar Age | 3.980 Gyr |
| Apparent Magnitude | V: 15.368 · G: 15.057 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.088600 AU |
| Orbital Period | 10.035 days |
| Mean Orbital Velocity | 96 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.8100° |
| Mean Bulk Density | 0.95 g/cm³ (23.7 km/s vesc) |
| Insolation Flux | 100.7790 S⊕ (~137,160 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3017.100 LY (925.037 pc) |