HD 4208 b
Astrophysical Synthesis & Habitability Characterization
HD 4208 b is a confirmed gas giant exoplanet orbiting the star HD 4208, located approximately 111.5 light-years (34.19 parsecs) from the Solar System. First announced in 2001 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 13.9 Earth radii (1.24 Jupiter radii) and has a measured mass of 257.442 Earth masses (0.81 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.53 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.33 g⊕ (13.04 m/s²), and an escape velocity of 48.1 km/s.
In its orbital architecture around HD 4208, HD 4208 b completes one full revolution every 832.97 Earth days (2.28Julian years) at a semi-major axis of 1.662 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 21.7 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.042 (ranging from 1.5922 AU at periapsis to 1.7318 AU at apoapsis), the planet experiences minimal orbital distance variation.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.900 R⊕, HD 4208 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star HD 4208 is classified as a solar-type yellow star of spectral type G7 V Fe-1 CH-0.5 with an effective photospheric temperature of 5,717 K, a radius of 0.846 R☉, a mass of 0.883 M☉, an estimated bolometric luminosity of 0.686 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.813 Gyr and a metallicity of [Fe/H] = -0.28 dex (metal-poor relative to the Sun). From Earth, HD 4208 shines at apparent V-band magnitude 7.783 (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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 4208 |
| Spectral Type | G7 V Fe-1 CH-0.5 |
| Effective Temp (Teff) | 5,717 K |
| Stellar Radius | 0.8460 R☉ |
| Stellar Mass | 0.8830 M☉ |
| Bolometric Luminosity | 0.686 L☉ |
| Metallicity [Fe/H] | -0.280 dex |
| Stellar Age | 3.813 Gyr |
| Apparent Magnitude | V: 7.783 · G: 7.611 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.662000 AU |
| Orbital Period | 832.97 days |
| Mean Orbital Velocity | 21.7 km/s |
| Orbital Eccentricity (e) | 0.04200 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.53 g/cm³ (48.1 km/s vesc) |
| Insolation Flux | 0.2878 S⊕ (~392 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 111.500 LY (34.194 pc) |