HD 191806 b
Astrophysical Synthesis & Habitability Characterization
HD 191806 b is a confirmed gas giant exoplanet orbiting the star HD 191806, located approximately 214.2 light-years (65.67 parsecs) from the Solar System. First announced in 2016 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.5 Earth radii (1.12 Jupiter radii) and has a measured mass of 2966.61 Earth masses (9.33 Jupiter masses). Combining its mass and radius yields a mean bulk density of 8.38 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 18.99 g⊕ (186.23 m/s²), and an escape velocity of 172.3 km/s.
In its orbital architecture around HD 191806, HD 191806 b completes one full revolution every 1603.389 Earth days (4.39Julian years) at a semi-major axis of 2.749 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 18.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.213 carries the world between 2.1635 AU at periapsis and 3.3345 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 12.500 R⊕, HD 191806 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 191806 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 6,010 K, a radius of 1.4022 R☉, a mass of 1.07 M☉, an estimated bolometric luminosity of 2.301 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.9 Gyr and a metallicity of [Fe/H] = 0.3 dex (metal-rich relative to the Sun). From Earth, HD 191806 shines at apparent V-band magnitude 8.09 (accessible to binoculars and small amateur telescopes) 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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 191806 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 6,010 K |
| Stellar Radius | 1.4022 R☉ |
| Stellar Mass | 1.0700 M☉ |
| Bolometric Luminosity | 2.301 L☉ |
| Metallicity [Fe/H] | 0.300 dex |
| Stellar Age | 2.900 Gyr |
| Apparent Magnitude | V: 8.090 · G: 7.933 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.749000 AU |
| Orbital Period | 1603.389 days |
| Mean Orbital Velocity | 18.7 km/s |
| Orbital Eccentricity (e) | 0.21300 |
| Orbital Inclination (i) | 66.5190° |
| Mean Bulk Density | 8.38 g/cm³ (172.3 km/s vesc) |
| Insolation Flux | 0.2951 S⊕ (~402 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 214.200 LY (65.667 pc) |