HD 43691 b
Astrophysical Synthesis & Habitability Characterization
HD 43691 b is a confirmed gas giant exoplanet orbiting the star HD 43691, located approximately 279.2 light-years (85.6 parsecs) from the Solar System. First announced in 2007 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.2 Earth radii (1.18 Jupiter radii) and has a measured mass of 810.467 Earth masses (2.55 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.94 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.65 g⊕ (45.6 m/s²), and an escape velocity of 87.7 km/s.
In its orbital architecture around HD 43691, HD 43691 b completes one full revolution every 36.999 Earth days at a semi-major axis of 0.238 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 70 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.0796 carries the world between 0.2191 AU at periapsis and 0.2569 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 762 K (+489°C / +912°F) and receiving 55.83 S⊕ (~75,981 W/m²), HD 43691 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 43691 is classified as a solar-type yellow star of spectral type G0 with an effective photospheric temperature of 6,093 K, a radius of 1.6 R☉, a mass of 1.32 M☉, an estimated bolometric luminosity of 3.166 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.39 Gyr and a metallicity of [Fe/H] = 0.33 dex (metal-rich relative to the Sun). From Earth, HD 43691 shines at apparent V-band magnitude 8.03 (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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 43691 |
| Spectral Type | G0 |
| Effective Temp (Teff) | 6,093 K |
| Stellar Radius | 1.6000 R☉ |
| Stellar Mass | 1.3200 M☉ |
| Bolometric Luminosity | 3.166 L☉ |
| Metallicity [Fe/H] | 0.330 dex |
| Stellar Age | 2.390 Gyr |
| Apparent Magnitude | V: 8.030 · G: 7.897 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.238000 AU |
| Orbital Period | 36.999 days |
| Mean Orbital Velocity | 70 km/s |
| Orbital Eccentricity (e) | 0.07960 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.94 g/cm³ (87.7 km/s vesc) |
| Insolation Flux | 55.8272 S⊕ (~75,981 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 279.200 LY (85.601 pc) |