HD 218566 b
Astrophysical Synthesis & Habitability Characterization
HD 218566 b is a confirmed gas giant exoplanet orbiting the star HD 218566, located approximately 94 light-years (28.83 parsecs) from the Solar System. First announced in 2010 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 9.32 Earth radii (0.83 Jupiter radii) and has a measured mass of 63.566 Earth masses (0.2 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.43 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.73 g⊕ (7.16 m/s²), and an escape velocity of 29.2 km/s.
In its orbital architecture around HD 218566, HD 218566 b completes one full revolution every 225.7 Earth days at a semi-major axis of 0.69 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 33.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.3, swinging from 0.483 AU at periapsis out to 0.897 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 9.320 R⊕, HD 218566 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 HD 218566 is classified as an orange K-type star of spectral type K3V with an effective photospheric temperature of 4,730 K, a radius of 0.85 R☉, a mass of 0.76 M☉, an estimated bolometric luminosity of 0.324 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.5 Gyr and a metallicity of [Fe/H] = 0.28 dex (metal-rich relative to the Sun). From Earth, HD 218566 shines at apparent V-band magnitude 8.6 (accessible to binoculars and small amateur telescopes) in the Southern 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 218566 |
| Spectral Type | K3V |
| Effective Temp (Teff) | 4,730 K |
| Stellar Radius | 0.8500 R☉ |
| Stellar Mass | 0.7600 M☉ |
| Bolometric Luminosity | 0.324 L☉ |
| Metallicity [Fe/H] | 0.280 dex |
| Stellar Age | 8.500 Gyr |
| Apparent Magnitude | V: 8.600 · G: 8.274 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.690000 AU |
| Orbital Period | 225.7 days |
| Mean Orbital Velocity | 33.3 km/s |
| Orbital Eccentricity (e) | 0.30000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.43 g/cm³ (29.2 km/s vesc) |
| Insolation Flux | 0.7414 S⊕ (~1,009 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 94.000 LY (28.827 pc) |