HD 168746 b
Astrophysical Synthesis & Habitability Characterization
HD 168746 b is a confirmed gas giant exoplanet orbiting the star HD 168746, located approximately 135.6 light-years (41.57 parsecs) from the Solar System. First announced in 2002 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 11.1 Earth radii (0.99 Jupiter radii) and has a measured mass of 85.814 Earth masses (0.27 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.35 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.7 g⊕ (6.86 m/s²), and an escape velocity of 31.1 km/s.
In its orbital architecture around HD 168746, HD 168746 b completes one full revolution every 6.404 Earth days at a semi-major axis of 0.07 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 118.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.11 carries the world between 0.0623 AU at periapsis and 0.0777 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 900 K (+627°C / +1161°F) and receiving 224.49 S⊕ (~305,531 W/m²), HD 168746 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 168746 is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 5,570 K, a radius of 1.09 R☉, a mass of 1.07 M☉, an estimated bolometric luminosity of 1.026 L☉. Stellar evolution modeling indicates an estimated stellar age of 8 Gyr and a metallicity of [Fe/H] = -0.08 dex (near-solar heavy-element abundance). From Earth, HD 168746 shines at apparent V-band magnitude 7.95 (accessible to binoculars and small amateur telescopes) in the Southern 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 168746 |
| Spectral Type | G5 |
| Effective Temp (Teff) | 5,570 K |
| Stellar Radius | 1.0900 R☉ |
| Stellar Mass | 1.0700 M☉ |
| Bolometric Luminosity | 1.026 L☉ |
| Metallicity [Fe/H] | -0.080 dex |
| Stellar Age | 8.000 Gyr |
| Apparent Magnitude | V: 7.950 · G: 7.772 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.070000 AU |
| Orbital Period | 6.404 days |
| Mean Orbital Velocity | 118.9 km/s |
| Orbital Eccentricity (e) | 0.11000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.35 g/cm³ (31.1 km/s vesc) |
| Insolation Flux | 224.4898 S⊕ (~305,531 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 135.600 LY (41.568 pc) |