HD 51608 c
Astrophysical Synthesis & Habitability Characterization
HD 51608 c is a confirmed sub-neptune exoplanet orbiting the star HD 51608, located approximately 114.3 light-years (35.06 parsecs) from the Solar System. First announced in 2019 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.87 Earth radii (0.35 Jupiter radii) and has a measured mass of 14.31 Earth masses. Combining its mass and radius yields a mean bulk density of 1.36 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.96 g⊕ (9.41 m/s²), and an escape velocity of 21.5 km/s.
In its orbital architecture around HD 51608, HD 51608 c completes one full revolution every 95.945 Earth days at a semi-major axis of 0.3809 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 43.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.14 carries the world between 0.3276 AU at periapsis and 0.4342 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 401 K (+128°C / +262°F) and receiving 3.93 S⊕ (~5,347 W/m²), HD 51608 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 51608 is classified as a solar-type yellow star of spectral type G7 V with an effective photospheric temperature of 5,358 K, a radius of 0.9161 R☉, a mass of 0.8 M☉, an estimated bolometric luminosity of 0.621 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.07 dex (near-solar heavy-element abundance). From Earth, HD 51608 shines at apparent V-band magnitude 8.17 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 51608 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 51608 c sharing its stellar neighborhood alongside HD 51608 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 51608 |
| Spectral Type | G7 V |
| Effective Temp (Teff) | 5,358 K |
| Stellar Radius | 0.9161 R☉ |
| Stellar Mass | 0.8000 M☉ |
| Bolometric Luminosity | 0.621 L☉ |
| Metallicity [Fe/H] | -0.070 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 8.170 · G: 7.961 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.380900 AU |
| Orbital Period | 95.945 days |
| Mean Orbital Velocity | 43.2 km/s |
| Orbital Eccentricity (e) | 0.14000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.36 g/cm³ (21.5 km/s vesc) |
| Insolation Flux | 3.9287 S⊕ (~5,347 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 114.300 LY (35.055 pc) |