HD 173416 b
Astrophysical Synthesis & Habitability Characterization
HD 173416 b is a confirmed gas giant exoplanet orbiting the star HD 173416, located approximately 431.1 light-years (132.18 parsecs) from the Solar System. First announced in 2008 by Xinglong Station using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.4 Earth radii (1.2 Jupiter radii) and has a measured mass of 585.122 Earth masses (1.84 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.34 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.26 g⊕ (31.97 m/s²), and an escape velocity of 73.9 km/s.
In its orbital architecture around HD 173416, HD 173416 b completes one full revolution every 322.03 Earth days at a semi-major axis of 1.158 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 39.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.208 carries the world between 0.9171 AU at periapsis and 1.3989 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 771 K (+498°C / +928°F) and receiving 58.15 S⊕ (~79,148 W/m²), HD 173416 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 173416 is classified as a solar-type yellow star of spectral type G8 with an effective photospheric temperature of 4,683 K, a radius of 13.5 R☉, a mass of 2 M☉, an estimated bolometric luminosity of 78.642 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.73 Gyr and a metallicity of [Fe/H] = -0.22 dex (metal-poor relative to the Sun). From Earth, HD 173416 shines at apparent V-band magnitude 6.042 (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: Xinglong Station · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 173416 |
| Spectral Type | G8 |
| Effective Temp (Teff) | 4,683 K |
| Stellar Radius | 13.5000 R☉ |
| Stellar Mass | 2.0000 M☉ |
| Bolometric Luminosity | 78.642 L☉ |
| Metallicity [Fe/H] | -0.220 dex |
| Stellar Age | 1.730 Gyr |
| Apparent Magnitude | V: 6.042 · G: 5.757 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.158000 AU |
| Orbital Period | 322.03 days |
| Mean Orbital Velocity | 39.1 km/s |
| Orbital Eccentricity (e) | 0.20800 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.34 g/cm³ (73.9 km/s vesc) |
| Insolation Flux | 58.1544 S⊕ (~79,148 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 431.100 LY (132.184 pc) |