HD 168009 b
Astrophysical Synthesis & Habitability Characterization
HD 168009 b is a confirmed sub-neptune exoplanet orbiting the star HD 168009, located approximately 76 light-years (23.3 parsecs) from the Solar System. First announced in 2021 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.05 Earth radii (0.27 Jupiter radii) and has a measured mass of 9.535 Earth masses. Combining its mass and radius yields a mean bulk density of 1.85 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 19.8 km/s.
In its orbital architecture around HD 168009, HD 168009 b completes one full revolution every 15.148 Earth days at a semi-major axis of 0.1192 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 85.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.12 carries the world between 0.1049 AU at periapsis and 0.1335 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 888 K (+615°C / +1139°F) and receiving 99.37 S⊕ (~135,247 W/m²), HD 168009 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 168009 is classified as a solar-type yellow star of spectral type G2V with an effective photospheric temperature of 5,778 K, a radius of 1.2095 R☉, a mass of 0.9861 M☉, an estimated bolometric luminosity of 1.463 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.68 Gyr and a metallicity of [Fe/H] = 0.018 dex (near-solar heavy-element abundance). From Earth, HD 168009 shines at apparent V-band magnitude 6.295 (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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 168009 |
| Spectral Type | G2V |
| Effective Temp (Teff) | 5,778 K |
| Stellar Radius | 1.2095 R☉ |
| Stellar Mass | 0.9861 M☉ |
| Bolometric Luminosity | 1.463 L☉ |
| Metallicity [Fe/H] | 0.018 dex |
| Stellar Age | 9.680 Gyr |
| Apparent Magnitude | V: 6.295 · G: 6.141 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.119200 AU |
| Orbital Period | 15.148 days |
| Mean Orbital Velocity | 85.6 km/s |
| Orbital Eccentricity (e) | 0.12000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.85 g/cm³ (19.8 km/s vesc) |
| Insolation Flux | 99.3735 S⊕ (~135,247 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 76.000 LY (23.303 pc) |