HIP 91258 b
Astrophysical Synthesis & Habitability Characterization
HIP 91258 b is a confirmed gas giant exoplanet orbiting the star HIP 91258, located approximately 149.7 light-years (45.89 parsecs) from the Solar System. First announced in 2013 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.7 Earth radii (1.22 Jupiter radii) and has a measured mass of 346.435 Earth masses (1.09 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.74 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.85 g⊕ (18.14 m/s²), and an escape velocity of 56.3 km/s.
In its orbital architecture around HIP 91258, HIP 91258 b completes one full revolution every 5.051 Earth days at a semi-major axis of 0.06 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 129.2 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.02 (ranging from 0.0588 AU at periapsis to 0.0612 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1025 K (+752°C / +1386°F) and receiving 166.61 S⊕ (~226,754 W/m²), HIP 91258 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HIP 91258 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,519 K, a radius of 0.89 R☉, a mass of 0.97 M☉, an estimated bolometric luminosity of 0.659 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.4 Gyr and a metallicity of [Fe/H] = 0.23 dex (metal-rich relative to the Sun). From Earth, HIP 91258 shines at apparent V-band magnitude 8.65 (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 | HIP 91258 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,519 K |
| Stellar Radius | 0.8900 R☉ |
| Stellar Mass | 0.9700 M☉ |
| Bolometric Luminosity | 0.659 L☉ |
| Metallicity [Fe/H] | 0.230 dex |
| Stellar Age | 2.400 Gyr |
| Apparent Magnitude | V: 8.650 · G: 8.450 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.060000 AU |
| Orbital Period | 5.051 days |
| Mean Orbital Velocity | 129.2 km/s |
| Orbital Eccentricity (e) | 0.02000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.74 g/cm³ (56.3 km/s vesc) |
| Insolation Flux | 166.6086 S⊕ (~226,754 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 149.700 LY (45.885 pc) |