HD 87646 b
Astrophysical Synthesis & Habitability Characterization
HD 87646 b is a confirmed gas giant exoplanet orbiting the star HD 87646, located approximately 240 light-years (73.58 parsecs) from the Solar System. First announced in 2016 by Apache Point Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.4 Earth radii (1.11 Jupiter radii) and has a measured mass of 3941.092 Earth masses (12.4 Jupiter masses). Combining its mass and radius yields a mean bulk density of 11.4 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 25.63 g⊕ (251.34 m/s²), and an escape velocity of 199.4 km/s.
In its orbital architecture around HD 87646, HD 87646 b completes one full revolution every 13.481 Earth days at a semi-major axis of 0.117 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 94.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.05 carries the world between 0.1112 AU at periapsis and 0.1229 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1013 K (+740°C / +1364°F) and receiving 665.81 S⊕ (~906,170 W/m²), HD 87646 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 87646 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,770 K, a radius of 1.55 R☉, a mass of 1.12 M☉, an estimated bolometric luminosity of 2.389 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.17 dex (metal-poor relative to the Sun). From Earth, HD 87646 shines at apparent V-band magnitude 8.07 (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: Apache Point Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 87646 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,770 K |
| Stellar Radius | 1.5500 R☉ |
| Stellar Mass | 1.1200 M☉ |
| Bolometric Luminosity | 2.389 L☉ |
| Metallicity [Fe/H] | -0.170 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 8.070 · G: 7.930 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.117000 AU |
| Orbital Period | 13.481 days |
| Mean Orbital Velocity | 94.4 km/s |
| Orbital Eccentricity (e) | 0.05000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 11.4 g/cm³ (199.4 km/s vesc) |
| Insolation Flux | 665.8120 S⊕ (~906,170 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 240.000 LY (73.584 pc) |