HD 217107 c
Astrophysical Synthesis & Habitability Characterization
HD 217107 c is a confirmed gas giant exoplanet orbiting the star HD 217107, located approximately 65.4 light-years (20.06 parsecs) from the Solar System. First announced in 2005 by Lick Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.9 Earth radii (1.15 Jupiter radii) and has a measured mass of 1388.91 Earth masses (4.37 Jupiter masses). Combining its mass and radius yields a mean bulk density of 3.57 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 8.35 g⊕ (81.89 m/s²), and an escape velocity of 116.1 km/s.
In its orbital architecture around HD 217107, HD 217107 c completes one full revolution every 5138.7 Earth days (14.07Julian years) at a semi-major axis of 5.922 AU (a wide outer-system orbit beyond Jupiter's 5.20 AU distance in our Solar System). Its mean orbital velocity is approximately 12.5 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.3918, swinging from 3.6018 AU at periapsis out to 8.2422 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 123 K (-150°C / -238°F) and an incident flux of 0.04 S⊕ (~49 W/m²), surface water and volatile species on HD 217107 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 217107 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,622 K, a radius of 1.2245 R☉, a mass of 1.045 M☉, an estimated bolometric luminosity of 1.344 L☉. Stellar evolution modeling indicates an estimated stellar age of 11.9 Gyr and a metallicity of [Fe/H] = 0.37 dex (metal-rich relative to the Sun). From Earth, HD 217107 shines at apparent V-band magnitude 6.155 (visible to the unaided human eye under dark skies) in the Southern celestial hemisphere. The HD 217107 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 217107 c sharing its stellar neighborhood alongside HD 217107 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: Lick Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 217107 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,622 K |
| Stellar Radius | 1.2245 R☉ |
| Stellar Mass | 1.0450 M☉ |
| Bolometric Luminosity | 1.344 L☉ |
| Metallicity [Fe/H] | 0.370 dex |
| Stellar Age | 11.900 Gyr |
| Apparent Magnitude | V: 6.155 · G: 5.964 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 5.922000 AU |
| Orbital Period | 5138.7 days |
| Mean Orbital Velocity | 12.5 km/s |
| Orbital Eccentricity (e) | 0.39180 |
| Orbital Inclination (i) | 88.0000° |
| Mean Bulk Density | 3.57 g/cm³ (116.1 km/s vesc) |
| Insolation Flux | 0.0357 S⊕ (~49 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 65.400 LY (20.062 pc) |