HD 178911 B b
Astrophysical Synthesis & Habitability Characterization
HD 178911 B b is a confirmed gas giant exoplanet orbiting the star HD 178911 B, located approximately 133.6 light-years (40.97 parsecs) from the Solar System. First announced in 2001 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 12.6 Earth radii (1.12 Jupiter radii) and has a measured mass of 2552.175 Earth masses (8.03 Jupiter masses). Combining its mass and radius yields a mean bulk density of 7.04 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 16.08 g⊕ (157.69 m/s²), and an escape velocity of 159.2 km/s.
In its orbital architecture around HD 178911 B, HD 178911 B b completes one full revolution every 71.484 Earth days at a semi-major axis of 0.34 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 51.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.11 carries the world between 0.3026 AU at periapsis and 0.3774 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 480 K (+207°C / +405°F) and receiving 7.83 S⊕ (~10,659 W/m²), HD 178911 B b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 178911 B is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 5,588 K, a radius of 1.08 R☉, a mass of 1.24 M☉, an estimated bolometric luminosity of 1.02 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.24 dex (metal-rich relative to the Sun). From Earth, HD 178911 B shines at apparent V-band magnitude 7.97 (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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 178911 B |
| Spectral Type | G5 |
| Effective Temp (Teff) | 5,588 K |
| Stellar Radius | 1.0800 R☉ |
| Stellar Mass | 1.2400 M☉ |
| Bolometric Luminosity | 1.02 L☉ |
| Metallicity [Fe/H] | 0.240 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 7.970 · G: 7.867 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.340000 AU |
| Orbital Period | 71.484 days |
| Mean Orbital Velocity | 51.7 km/s |
| Orbital Eccentricity (e) | 0.11000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 7.04 g/cm³ (159.2 km/s vesc) |
| Insolation Flux | 7.8319 S⊕ (~10,659 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 133.600 LY (40.973 pc) |