HD 161178 b
Astrophysical Synthesis & Habitability Characterization
HD 161178 b is a confirmed gas giant exoplanet orbiting the star HD 161178, located approximately 349.6 light-years (107.19 parsecs) from the Solar System. First announced in 2021 by Okayama Astrophysical Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.1 Earth radii (1.26 Jupiter radii) and has a measured mass of 181.162 Earth masses (0.57 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.36 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.91 g⊕ (8.92 m/s²), and an escape velocity of 40.1 km/s.
In its orbital architecture around HD 161178, HD 161178 b completes one full revolution every 279.3 Earth days at a semi-major axis of 0.85 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 33.1 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.044 (ranging from 0.8126 AU at periapsis to 0.8874 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 828 K (+555°C / +1031°F) and receiving 78.01 S⊕ (~106,167 W/m²), HD 161178 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 161178 is classified as a solar-type yellow star of spectral type G9 III with an effective photospheric temperature of 4,786 K, a radius of 10.95 R☉, a mass of 1.06 M☉, an estimated bolometric luminosity of 56.443 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.21 dex (metal-poor relative to the Sun). From Earth, HD 161178 shines at apparent V-band magnitude 5.884 (visible to the unaided human eye under dark skies) 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: Okayama Astrophysical Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 161178 |
| Spectral Type | G9 III |
| Effective Temp (Teff) | 4,786 K |
| Stellar Radius | 10.9500 R☉ |
| Stellar Mass | 1.0600 M☉ |
| Bolometric Luminosity | 56.443 L☉ |
| Metallicity [Fe/H] | -0.210 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 5.884 · G: 5.600 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.850000 AU |
| Orbital Period | 279.3 days |
| Mean Orbital Velocity | 33.1 km/s |
| Orbital Eccentricity (e) | 0.04400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.36 g/cm³ (40.1 km/s vesc) |
| Insolation Flux | 78.0069 S⊕ (~106,167 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 349.600 LY (107.188 pc) |