HD 204313 c
Astrophysical Synthesis & Habitability Characterization
HD 204313 c is a confirmed sub-neptune exoplanet orbiting the star HD 204313, located approximately 155.9 light-years (47.8 parsecs) from the Solar System. First announced in 2015 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.31 Earth radii (0.38 Jupiter radii) and has a measured mass of 17.163 Earth masses. Combining its mass and radius yields a mean bulk density of 1.18 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.92 g⊕ (9.02 m/s²), and an escape velocity of 22.3 km/s.
In its orbital architecture around HD 204313, HD 204313 c completes one full revolution every 34.959 Earth days at a semi-major axis of 0.211 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 65.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.059 carries the world between 0.1986 AU at periapsis and 0.2234 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 635 K (+362°C / +684°F) and receiving 28.26 S⊕ (~38,468 W/m²), HD 204313 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 204313 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,767 K, a radius of 1.1 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.201 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.38 Gyr and a metallicity of [Fe/H] = 0.18 dex (metal-rich relative to the Sun). From Earth, HD 204313 shines at apparent V-band magnitude 7.99 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 204313 system is a multi-planet architecture hosting 3 confirmed worlds, with HD 204313 c sharing its stellar neighborhood alongside HD 204313 b, HD 204313 e.
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 204313 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,767 K |
| Stellar Radius | 1.1000 R☉ |
| Stellar Mass | 1.0300 M☉ |
| Bolometric Luminosity | 1.201 L☉ |
| Metallicity [Fe/H] | 0.180 dex |
| Stellar Age | 3.380 Gyr |
| Apparent Magnitude | V: 7.990 · G: 7.832 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.211000 AU |
| Orbital Period | 34.959 days |
| Mean Orbital Velocity | 65.7 km/s |
| Orbital Eccentricity (e) | 0.05900 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.18 g/cm³ (22.3 km/s vesc) |
| Insolation Flux | 28.2644 S⊕ (~38,468 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 155.900 LY (47.795 pc) |