HD 164509 b
Astrophysical Synthesis & Habitability Characterization
HD 164509 b is a confirmed gas giant exoplanet orbiting the star HD 164509, located approximately 173.2 light-years (53.11 parsecs) from the Solar System. First announced in 2012 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.3 Earth radii (1.28 Jupiter radii) and has a measured mass of 140.799 Earth masses (0.44 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.27 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.69 g⊕ (6.77 m/s²), and an escape velocity of 35.1 km/s.
In its orbital architecture around HD 164509, HD 164509 b completes one full revolution every 280.17 Earth days at a semi-major axis of 0.87 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 33.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.238 carries the world between 0.6629 AU at periapsis and 1.0771 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 14.300 R⊕, HD 164509 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 HD 164509 is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 5,859 K, a radius of 1.11 R☉, a mass of 1.12 M☉, an estimated bolometric luminosity of 1.303 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.32 Gyr and a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, HD 164509 shines at apparent V-band magnitude 8.1 (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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 164509 |
| Spectral Type | G5 |
| Effective Temp (Teff) | 5,859 K |
| Stellar Radius | 1.1100 R☉ |
| Stellar Mass | 1.1200 M☉ |
| Bolometric Luminosity | 1.303 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | 2.320 Gyr |
| Apparent Magnitude | V: 8.100 · G: 7.956 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.870000 AU |
| Orbital Period | 280.17 days |
| Mean Orbital Velocity | 33.8 km/s |
| Orbital Eccentricity (e) | 0.23800 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.27 g/cm³ (35.1 km/s vesc) |
| Insolation Flux | 1.7417 S⊕ (~2,370 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 173.200 LY (53.112 pc) |