HD 66428 c
Astrophysical Synthesis & Habitability Characterization
HD 66428 c 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 2021 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.5 Earth radii (1.2 Jupiter radii) and has a measured mass of 560.649 Earth masses (1.76 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.26 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.08 g⊕ (30.2 m/s²), and an escape velocity of 72.1 km/s.
In its orbital architecture around HD 66428, HD 66428 c completes one full revolution every 10478.844 Earth days (28.69Julian years) at a semi-major axis of 9.408 AU (a wide outer-system orbit beyond Jupiter's 5.20 AU distance in our Solar System). Its mean orbital velocity is approximately 9.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.207 carries the world between 7.4605 AU at periapsis and 11.3555 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 96 K (-177°C / -287°F) and an incident flux of 0.01 S⊕ (~19 W/m²), surface water and volatile species on HD 66428 c 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 c sharing its stellar neighborhood alongside HD 66428 b.
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: Multiple Observatories · 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) | 9.408000 AU |
| Orbital Period | 10478.844 days |
| Mean Orbital Velocity | 9.8 km/s |
| Orbital Eccentricity (e) | 0.20700 |
| Orbital Inclination (i) | 93.9380° |
| Mean Bulk Density | 1.26 g/cm³ (72.1 km/s vesc) |
| Insolation Flux | 0.0141 S⊕ (~19 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 173.800 LY (53.282 pc) |