HD 118203 b
Astrophysical Synthesis & Habitability Characterization
HD 118203 b is a confirmed gas giant exoplanet orbiting the star HD 118203, located approximately 300.9 light-years (92.26 parsecs) from the Solar System. First announced in 2005 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.778 Earth radii (1.14 Jupiter radii) and has a measured mass of 680.153 Earth masses (2.14 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 4.17 g⊕ (40.89 m/s²), and an escape velocity of 81.6 km/s.
In its orbital architecture around HD 118203, HD 118203 b completes one full revolution every 6.135 Earth days at a semi-major axis of 0.0713 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 126.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.3136, swinging from 0.0489 AU at periapsis out to 0.0937 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1361 K (+1088°C / +1990°F) and receiving 593.40 S⊕ (~807,617 W/m²), HD 118203 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 118203 is classified as an orange K-type star of spectral type K0 IV with an effective photospheric temperature of 5,742 K, a radius of 2.04 R☉, a mass of 1.27 M☉, an estimated bolometric luminosity of 4.059 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.73 Gyr and a metallicity of [Fe/H] = 0.287 dex (metal-rich relative to the Sun). From Earth, HD 118203 shines at apparent V-band magnitude 8.05 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 118203 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 118203 b sharing its stellar neighborhood alongside HD 118203 c.
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 118203 |
| Spectral Type | K0 IV |
| Effective Temp (Teff) | 5,742 K |
| Stellar Radius | 2.0400 R☉ |
| Stellar Mass | 1.2700 M☉ |
| Bolometric Luminosity | 4.059 L☉ |
| Metallicity [Fe/H] | 0.287 dex |
| Stellar Age | 4.730 Gyr |
| Apparent Magnitude | V: 8.050 · G: 7.893 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.071300 AU |
| Orbital Period | 6.135 days |
| Mean Orbital Velocity | 126.4 km/s |
| Orbital Eccentricity (e) | 0.31360 |
| Orbital Inclination (i) | 88.4800° |
| Mean Bulk Density | 1.8 g/cm³ (81.6 km/s vesc) |
| Insolation Flux | 593.4000 S⊕ (~807,617 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 300.900 LY (92.259 pc) |