HD 217786 b
Astrophysical Synthesis & Habitability Characterization
HD 217786 b is a confirmed gas giant exoplanet orbiting the star HD 217786, located approximately 181 light-years (55.49 parsecs) from the Solar System. First announced in 2011 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.3 Earth radii (1.1 Jupiter radii) and has a measured mass of 4402.559 Earth masses (13.85 Jupiter masses). Combining its mass and radius yields a mean bulk density of 13.05 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 29.1 g⊕ (285.37 m/s²), and an escape velocity of 211.6 km/s.
In its orbital architecture around HD 217786, HD 217786 b completes one full revolution every 1301.36 Earth days (3.56Julian years) at a semi-major axis of 2.446 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 20.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.311, swinging from 1.6853 AU at periapsis out to 3.2067 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 12.300 R⊕, HD 217786 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 217786 is classified as a warm F-type star of spectral type F8 V with an effective photospheric temperature of 5,966 K, a radius of 1.27 R☉, a mass of 1.14 M☉, an estimated bolometric luminosity of 1.833 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.6 Gyr and a metallicity of [Fe/H] = -0.135 dex (metal-poor relative to the Sun). From Earth, HD 217786 shines at apparent V-band magnitude 7.78 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 217786 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 217786 b sharing its stellar neighborhood alongside HD 217786 c.
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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 217786 |
| Spectral Type | F8 V |
| Effective Temp (Teff) | 5,966 K |
| Stellar Radius | 1.2700 R☉ |
| Stellar Mass | 1.1400 M☉ |
| Bolometric Luminosity | 1.833 L☉ |
| Metallicity [Fe/H] | -0.135 dex |
| Stellar Age | 7.600 Gyr |
| Apparent Magnitude | V: 7.780 · G: 7.636 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.446000 AU |
| Orbital Period | 1301.36 days |
| Mean Orbital Velocity | 20.4 km/s |
| Orbital Eccentricity (e) | 0.31100 |
| Orbital Inclination (i) | 69.7670° |
| Mean Bulk Density | 13.05 g/cm³ (211.6 km/s vesc) |
| Insolation Flux | 0.3159 S⊕ (~430 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 181.000 LY (55.485 pc) |