HD 111591 b
Astrophysical Synthesis & Habitability Characterization
HD 111591 b is a confirmed gas giant exoplanet orbiting the star HD 111591, located approximately 372.4 light-years (114.17 parsecs) from the Solar System. First announced in 2017 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.9 Earth radii (1.15 Jupiter radii) and has a measured mass of 1398.452 Earth masses (4.4 Jupiter masses). Combining its mass and radius yields a mean bulk density of 3.59 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 8.4 g⊕ (82.38 m/s²), and an escape velocity of 116.5 km/s.
In its orbital architecture around HD 111591, HD 111591 b completes one full revolution every 1056.4 Earth days (2.89Julian years) at a semi-major axis of 2.5 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 25.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.26, swinging from 1.85 AU at periapsis out to 3.15 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 422 K (+149°C / +300°F) and receiving 6.09 S⊕ (~8,290 W/m²), HD 111591 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 111591 is classified as an orange K-type star of spectral type K0 III with an effective photospheric temperature of 4,884 K, a radius of 8.03 R☉, a mass of 1.94 M☉, an estimated bolometric luminosity of 32.917 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.41 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, HD 111591 shines at apparent V-band magnitude 6.417 (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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 111591 |
| Spectral Type | K0 III |
| Effective Temp (Teff) | 4,884 K |
| Stellar Radius | 8.0300 R☉ |
| Stellar Mass | 1.9400 M☉ |
| Bolometric Luminosity | 32.917 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 1.410 Gyr |
| Apparent Magnitude | V: 6.417 · G: 6.152 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.500000 AU |
| Orbital Period | 1056.4 days |
| Mean Orbital Velocity | 25.7 km/s |
| Orbital Eccentricity (e) | 0.26000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 3.59 g/cm³ (116.5 km/s vesc) |
| Insolation Flux | 6.0912 S⊕ (~8,290 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 372.400 LY (114.166 pc) |