HD 108863 b
Astrophysical Synthesis & Habitability Characterization
HD 108863 b is a confirmed gas giant exoplanet orbiting the star HD 108863, located approximately 537.3 light-years (164.74 parsecs) from the Solar System. First announced in 2011 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 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 767.242 Earth masses (2.41 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.8 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.34 g⊕ (42.56 m/s²), and an escape velocity of 85 km/s.
In its orbital architecture around HD 108863, HD 108863 b completes one full revolution every 437.7 Earth days (1.2Julian years) at a semi-major axis of 1.32 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 32.8 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.032 (ranging from 1.2778 AU at periapsis to 1.3622 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 491 K (+218°C / +424°F) and receiving 9.64 S⊕ (~13,123 W/m²), HD 108863 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 108863 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 4,878 K, a radius of 5.74 R☉, a mass of 1.59 M☉, an estimated bolometric luminosity of 16.737 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.8 Gyr and a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, HD 108863 shines at apparent V-band magnitude 7.71 (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 108863 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 4,878 K |
| Stellar Radius | 5.7400 R☉ |
| Stellar Mass | 1.5900 M☉ |
| Bolometric Luminosity | 16.737 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | 1.800 Gyr |
| Apparent Magnitude | V: 7.710 · G: 7.454 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.320000 AU |
| Orbital Period | 437.7 days |
| Mean Orbital Velocity | 32.8 km/s |
| Orbital Eccentricity (e) | 0.03200 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.8 g/cm³ (85 km/s vesc) |
| Insolation Flux | 9.6419 S⊕ (~13,123 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 537.300 LY (164.742 pc) |