K2-118 b
Astrophysical Synthesis & Habitability Characterization
K2-118 b is a confirmed sub-neptune exoplanet orbiting the star K2-118, located approximately 1049.3 light-years (321.72 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1005% across the stellar disk), this world measures 2.54 Earth radii and has a measured mass of 6.99 Earth masses. Combining its mass and radius yields a mean bulk density of 2.35 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 18.6 km/s.
In its orbital architecture around K2-118, K2-118 b completes one full revolution every 50.921 Earth days at a semi-major axis of 0.245 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 52.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.2 carries the world between 0.196 AU at periapsis and 0.294 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 395 K (+122°C / +252°F) and receiving 4.30 S⊕ (~5,852 W/m²), K2-118 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-118 is classified as a stellar host with an effective photospheric temperature of 4,726 K, a radius of 0.7346 R☉, a mass of 0.7564 M☉, an estimated bolometric luminosity of 0.242 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.129 dex (metal-rich relative to the Sun). From Earth, K2-118 shines at apparent V-band magnitude 14 (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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-118 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,726 K |
| Stellar Radius | 0.7346 R☉ |
| Stellar Mass | 0.7564 M☉ |
| Bolometric Luminosity | 0.242 L☉ |
| Metallicity [Fe/H] | 0.129 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 14.000 · G: 13.748 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.245000 AU |
| Orbital Period | 50.921 days |
| Mean Orbital Velocity | 52.3 km/s |
| Orbital Eccentricity (e) | 0.20000 |
| Orbital Inclination (i) | 89.5000° |
| Mean Bulk Density | 2.35 g/cm³ (18.6 km/s vesc) |
| Insolation Flux | 4.3000 S⊕ (~5,852 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1049.300 LY (321.722 pc) |