HD 4203 c
Astrophysical Synthesis & Habitability Characterization
HD 4203 c is a confirmed gas giant exoplanet orbiting the star HD 4203, located approximately 265.4 light-years (81.38 parsecs) from the Solar System. First announced in 2014 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 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 689.66 Earth masses (2.17 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.62 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.9 g⊕ (38.25 m/s²), and an escape velocity of 80.6 km/s.
In its orbital architecture around HD 4203, HD 4203 c completes one full revolution every 6700 Earth days (18.34Julian years) at a semi-major axis of 6.95 AU (a wide outer-system orbit beyond Jupiter's 5.20 AU distance in our Solar System). Its mean orbital velocity is approximately 11.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.24 carries the world between 5.282 AU at periapsis and 8.618 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 125 K (-148°C / -234°F) and an incident flux of 0.04 S⊕ (~55 W/m²), surface water and volatile species on HD 4203 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 4203 is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 5,582 K, a radius of 1.498 R☉, a mass of 0.99 M☉, an estimated bolometric luminosity of 1.955 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.52 Gyr and a metallicity of [Fe/H] = 0.34 dex (metal-rich relative to the Sun). From Earth, HD 4203 shines at apparent V-band magnitude 8.7 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 4203 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 4203 c sharing its stellar neighborhood alongside HD 4203 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 4203 |
| Spectral Type | G5 |
| Effective Temp (Teff) | 5,582 K |
| Stellar Radius | 1.4980 R☉ |
| Stellar Mass | 0.9900 M☉ |
| Bolometric Luminosity | 1.955 L☉ |
| Metallicity [Fe/H] | 0.340 dex |
| Stellar Age | 8.520 Gyr |
| Apparent Magnitude | V: 8.700 · G: 8.515 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 6.950000 AU |
| Orbital Period | 6700 days |
| Mean Orbital Velocity | 11.3 km/s |
| Orbital Eccentricity (e) | 0.24000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.62 g/cm³ (80.6 km/s vesc) |
| Insolation Flux | 0.0406 S⊕ (~55 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 265.400 LY (81.380 pc) |