HD 5891 b
Astrophysical Synthesis & Habitability Characterization
HD 5891 b is a confirmed gas giant exoplanet orbiting the star HD 5891, located approximately 924.7 light-years (283.5 parsecs) from the Solar System. First announced in 2011 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 2425.043 Earth masses (7.63 Jupiter masses). Combining its mass and radius yields a mean bulk density of 6.68 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 15.27 g⊕ (149.75 m/s²), and an escape velocity of 155.2 km/s.
In its orbital architecture around HD 5891, HD 5891 b completes one full revolution every 177.11 Earth days at a semi-major axis of 0.64 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 39.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.5952 AU at periapsis and 0.6848 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 919 K (+646°C / +1195°F) and receiving 96.19 S⊕ (~130,916 W/m²), HD 5891 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 5891 is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 4,673 K, a radius of 10.64 R☉, a mass of 1.93 M☉, an estimated bolometric luminosity of 48.435 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.5 Gyr and a metallicity of [Fe/H] = -0.37 dex (metal-poor relative to the Sun). From Earth, HD 5891 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 5891 |
| Spectral Type | G5 |
| Effective Temp (Teff) | 4,673 K |
| Stellar Radius | 10.6400 R☉ |
| Stellar Mass | 1.9300 M☉ |
| Bolometric Luminosity | 48.435 L☉ |
| Metallicity [Fe/H] | -0.370 dex |
| Stellar Age | 1.500 Gyr |
| Apparent Magnitude | V: 8.090 · G: 7.798 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.640000 AU |
| Orbital Period | 177.11 days |
| Mean Orbital Velocity | 39.3 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 6.68 g/cm³ (155.2 km/s vesc) |
| Insolation Flux | 96.1914 S⊕ (~130,916 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 924.700 LY (283.502 pc) |