HIP 5158 b
Astrophysical Synthesis & Habitability Characterization
HIP 5158 b is a confirmed gas giant exoplanet orbiting the star HIP 5158, located approximately 168.3 light-years (51.6 parsecs) from the Solar System. First announced in 2009 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 451 Earth masses (1.42 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.99 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.44 g⊕ (23.93 m/s²), and an escape velocity of 64.4 km/s.
In its orbital architecture around HIP 5158, HIP 5158 b completes one full revolution every 345.72 Earth days at a semi-major axis of 0.89 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 28 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.52, swinging from 0.4272 AU at periapsis out to 1.3528 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.600 R⊕, HIP 5158 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star HIP 5158 is classified as a stellar host with an effective photospheric temperature of 4,962 K, a radius of 0.75 R☉, a mass of 0.78 M☉, an estimated bolometric luminosity of 0.306 L☉. Stellar evolution modeling indicates an estimated stellar age of 6 Gyr and a metallicity of [Fe/H] = 0.1 dex (metal-rich relative to the Sun). From Earth, HIP 5158 shines at apparent V-band magnitude 10.16 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The HIP 5158 system is a multi-planet architecture hosting 2 confirmed worlds, with HIP 5158 b sharing its stellar neighborhood alongside HIP 5158 c.
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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HIP 5158 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,962 K |
| Stellar Radius | 0.7500 R☉ |
| Stellar Mass | 0.7800 M☉ |
| Bolometric Luminosity | 0.306 L☉ |
| Metallicity [Fe/H] | 0.100 dex |
| Stellar Age | 6.000 Gyr |
| Apparent Magnitude | V: 10.160 · G: 9.802 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.890000 AU |
| Orbital Period | 345.72 days |
| Mean Orbital Velocity | 28 km/s |
| Orbital Eccentricity (e) | 0.52000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.99 g/cm³ (64.4 km/s vesc) |
| Insolation Flux | 0.1389 S⊕ (~189 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 168.300 LY (51.603 pc) |