HIP 65891 b
Astrophysical Synthesis & Habitability Characterization
HIP 65891 b is a confirmed gas giant exoplanet orbiting the star HIP 65891, located approximately 490.2 light-years (150.29 parsecs) from the Solar System. First announced in 2015 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.7 Earth radii (1.13 Jupiter radii) and has a measured mass of 1938.753 Earth masses (6.1 Jupiter masses). Combining its mass and radius yields a mean bulk density of 5.22 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 12.02 g⊕ (117.88 m/s²), and an escape velocity of 138.2 km/s.
In its orbital architecture around HIP 65891, HIP 65891 b completes one full revolution every 1089.6 Earth days (2.98Julian years) at a semi-major axis of 2.82 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 28.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.09 carries the world between 2.5662 AU at periapsis and 3.0738 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 429 K (+156°C / +313°F) and receiving 5.62 S⊕ (~7,645 W/m²), HIP 65891 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HIP 65891 is classified as an orange K-type star of spectral type K0 III with an effective photospheric temperature of 5,000 K, a radius of 8.93 R☉, a mass of 2.5 M☉, an estimated bolometric luminosity of 44.717 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.16 dex (metal-rich relative to the Sun). From Earth, HIP 65891 shines at apparent V-band magnitude 6.75 (accessible to binoculars and small amateur telescopes) in the Southern 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 | HIP 65891 |
| Spectral Type | K0 III |
| Effective Temp (Teff) | 5,000 K |
| Stellar Radius | 8.9300 R☉ |
| Stellar Mass | 2.5000 M☉ |
| Bolometric Luminosity | 44.717 L☉ |
| Metallicity [Fe/H] | 0.160 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 6.750 · G: 6.482 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.820000 AU |
| Orbital Period | 1089.6 days |
| Mean Orbital Velocity | 28.2 km/s |
| Orbital Eccentricity (e) | 0.09000 |
| Orbital Inclination (i) | 89.9000° |
| Mean Bulk Density | 5.22 g/cm³ (138.2 km/s vesc) |
| Insolation Flux | 5.6170 S⊕ (~7,645 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 490.200 LY (150.292 pc) |