K2-218 b
Astrophysical Synthesis & Habitability Characterization
K2-218 b is a confirmed sub-neptune exoplanet orbiting the star K2-218, located approximately 1285.3 light-years (394.08 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0546% across the stellar disk), this world measures 2.569 Earth radii and has a measured mass of 7.13 Earth masses. Combining its mass and radius yields a mean bulk density of 2.32 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 K2-218, K2-218 b completes one full revolution every 8.68 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.569 R⊕, K2-218 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star K2-218 is classified as a stellar host with an effective photospheric temperature of 5,757 K, a radius of 1.0082 R☉, a mass of 1.0475 M☉, an estimated bolometric luminosity of 1.002 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.25 dex (metal-rich relative to the Sun). From Earth, K2-218 shines at apparent V-band magnitude 12.92 (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 | K2-218 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,757 K |
| Stellar Radius | 1.0082 R☉ |
| Stellar Mass | 1.0475 M☉ |
| Bolometric Luminosity | 1.002 L☉ |
| Metallicity [Fe/H] | 0.250 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.920 · G: 12.714 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 8.68 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.4526° |
| Mean Bulk Density | 2.32 g/cm³ (18.6 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1285.300 LY (394.083 pc) |