HD 4308 b
Astrophysical Synthesis & Habitability Characterization
HD 4308 b is a confirmed sub-neptune exoplanet orbiting the star HD 4308, located approximately 71.8 light-years (22.02 parsecs) from the Solar System. First announced in 2005 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.12 Earth radii (0.37 Jupiter radii) and has a measured mass of 15.892 Earth masses. Combining its mass and radius yields a mean bulk density of 1.25 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 22 km/s.
In its orbital architecture around HD 4308, HD 4308 b completes one full revolution every 15.56 Earth days at a semi-major axis of 0.12 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 83.9 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 799 K (+526°C / +979°F) and receiving 68.81 S⊕ (~93,647 W/m²), HD 4308 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 4308 is classified as a solar-type yellow star of spectral type G5V with an effective photospheric temperature of 5,686 K, a radius of 1.02 R☉, a mass of 0.93 M☉, an estimated bolometric luminosity of 0.976 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.3 Gyr and a metallicity of [Fe/H] = -0.35 dex (metal-poor relative to the Sun). From Earth, HD 4308 shines at apparent V-band magnitude 6.55 (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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 4308 |
| Spectral Type | G5V |
| Effective Temp (Teff) | 5,686 K |
| Stellar Radius | 1.0200 R☉ |
| Stellar Mass | 0.9300 M☉ |
| Bolometric Luminosity | 0.976 L☉ |
| Metallicity [Fe/H] | -0.350 dex |
| Stellar Age | 4.300 Gyr |
| Apparent Magnitude | V: 6.550 · G: 6.376 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.120000 AU |
| Orbital Period | 15.56 days |
| Mean Orbital Velocity | 83.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.25 g/cm³ (22 km/s vesc) |
| Insolation Flux | 68.8078 S⊕ (~93,647 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 71.800 LY (22.016 pc) |