HD 66428 b
Astrophysical Synthesis & Habitability Characterization
HD 66428 b is a confirmed gas giant exoplanet orbiting the star HD 66428, located approximately 173.8 light-years (53.28 parsecs) from the Solar System. First announced in 2005 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 12.4 Earth radii (1.11 Jupiter radii) and has a measured mass of 3478.95 Earth masses (10.95 Jupiter masses). Combining its mass and radius yields a mean bulk density of 10.06 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 22.63 g⊕ (221.92 m/s²), and an escape velocity of 187.4 km/s.
In its orbital architecture around HD 66428, HD 66428 b completes one full revolution every 2269.817 Earth days (6.21Julian years) at a semi-major axis of 3.395 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 16.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.471, swinging from 1.796 AU at periapsis out to 4.994 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 159 K (-114°C / -173°F) and an incident flux of 0.11 S⊕ (~147 W/m²), surface water and volatile species on HD 66428 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 66428 is classified as a solar-type yellow star of spectral type G8 IV (+ G) with an effective photospheric temperature of 5,716 K, a radius of 1.13 R☉, a mass of 1.01 M☉, an estimated bolometric luminosity of 1.223 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.515 Gyr and a metallicity of [Fe/H] = 0.23 dex (metal-rich relative to the Sun). From Earth, HD 66428 shines at apparent V-band magnitude 8.25 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 66428 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 66428 b sharing its stellar neighborhood alongside HD 66428 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 66428 |
| Spectral Type | G8 IV (+ G) |
| Effective Temp (Teff) | 5,716 K |
| Stellar Radius | 1.1300 R☉ |
| Stellar Mass | 1.0100 M☉ |
| Bolometric Luminosity | 1.223 L☉ |
| Metallicity [Fe/H] | 0.230 dex |
| Stellar Age | 3.515 Gyr |
| Apparent Magnitude | V: 8.250 · G: 8.081 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 3.395000 AU |
| Orbital Period | 2269.817 days |
| Mean Orbital Velocity | 16.3 km/s |
| Orbital Eccentricity (e) | 0.47100 |
| Orbital Inclination (i) | 16.6390° |
| Mean Bulk Density | 10.06 g/cm³ (187.4 km/s vesc) |
| Insolation Flux | 0.1082 S⊕ (~147 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 173.800 LY (53.282 pc) |