Kepler-618 b
Astrophysical Synthesis & Habitability Characterization
Kepler-618 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-618, located approximately 3985.5 light-years (1221.96 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0487% across the stellar disk), this world measures 2.6 Earth radii and has a measured mass of 7.27 Earth masses. Combining its mass and radius yields a mean bulk density of 2.28 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 18.7 km/s.
In its orbital architecture around Kepler-618, Kepler-618 b completes one full revolution every 3.596 Earth days at a semi-major axis of 0.0449 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 135.8 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 1296 K (+1023°C / +1873°F) and receiving 677.57 S⊕ (~922,171 W/m²), Kepler-618 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-618 is classified as a stellar host with an effective photospheric temperature of 5,860 K, a radius of 1.08 R☉, a mass of 1.05 M☉, an estimated bolometric luminosity of 1.234 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.27 Gyr and a metallicity of [Fe/H] = 0.08 dex (metal-rich relative to the Sun). From Earth, Kepler-618 shines at apparent V-band magnitude 15.087 (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-618 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,860 K |
| Stellar Radius | 1.0800 R☉ |
| Stellar Mass | 1.0500 M☉ |
| Bolometric Luminosity | 1.234 L☉ |
| Metallicity [Fe/H] | 0.080 dex |
| Stellar Age | 4.270 Gyr |
| Apparent Magnitude | V: 15.087 · G: 14.804 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.044900 AU |
| Orbital Period | 3.596 days |
| Mean Orbital Velocity | 135.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 86.3400° |
| Mean Bulk Density | 2.28 g/cm³ (18.7 km/s vesc) |
| Insolation Flux | 677.5690 S⊕ (~922,171 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3985.500 LY (1221.960 pc) |