K2-217 b
Astrophysical Synthesis & Habitability Characterization
K2-217 b is a confirmed sub-neptune exoplanet orbiting the star K2-217, located approximately 1245.5 light-years (381.88 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0605% across the stellar disk), this world measures 3.579 Earth radii (0.32 Jupiter radii) and has a measured mass of 12.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.5 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 20.9 km/s.
In its orbital architecture around K2-217, K2-217 b completes one full revolution every 14.075 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 3.579 R⊕, K2-217 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 K2-217 is classified as a stellar host with an effective photospheric temperature of 5,967 K, a radius of 1.3337 R☉, a mass of 1.1027 M☉, an estimated bolometric luminosity of 2.023 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.04 dex (near-solar heavy-element abundance). From Earth, K2-217 shines at apparent V-band magnitude 12.264 (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 | K2-217 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,967 K |
| Stellar Radius | 1.3337 R☉ |
| Stellar Mass | 1.1027 M☉ |
| Bolometric Luminosity | 2.023 L☉ |
| Metallicity [Fe/H] | 0.040 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.264 · G: 12.028 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 14.075 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.0432° |
| Mean Bulk Density | 1.5 g/cm³ (20.9 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1245.500 LY (381.878 pc) |