HD 156668 c
Astrophysical Synthesis & Habitability Characterization
HD 156668 c is a confirmed gas giant exoplanet orbiting the star HD 156668, located approximately 79.4 light-years (24.33 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 6.17 Earth radii (0.55 Jupiter radii) and has a measured mass of 31.497 Earth masses (0.1 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.74 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.83 g⊕ (8.14 m/s²), and an escape velocity of 25.3 km/s.
In its orbital architecture around HD 156668, HD 156668 c completes one full revolution every 811.3 Earth days (2.22Julian years) at a semi-major axis of 1.57 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 21.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.089 carries the world between 1.4303 AU at periapsis and 1.7097 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 166 K (-107°C / -161°F) and an incident flux of 0.12 S⊕ (~159 W/m²), surface water and volatile species on HD 156668 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 156668 is classified as an orange K-type star of spectral type K2 with an effective photospheric temperature of 4,904 K, a radius of 0.7745 R☉, a mass of 0.7852 M☉, an estimated bolometric luminosity of 0.311 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.6 Gyr and a metallicity of [Fe/H] = 0.049 dex (near-solar heavy-element abundance). From Earth, HD 156668 shines at apparent V-band magnitude 8.43 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 156668 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 156668 c sharing its stellar neighborhood alongside HD 156668 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 156668 |
| Spectral Type | K2 |
| Effective Temp (Teff) | 4,904 K |
| Stellar Radius | 0.7745 R☉ |
| Stellar Mass | 0.7852 M☉ |
| Bolometric Luminosity | 0.311 L☉ |
| Metallicity [Fe/H] | 0.049 dex |
| Stellar Age | 8.600 Gyr |
| Apparent Magnitude | V: 8.430 · G: 8.108 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.570000 AU |
| Orbital Period | 811.3 days |
| Mean Orbital Velocity | 21.1 km/s |
| Orbital Eccentricity (e) | 0.08900 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.74 g/cm³ (25.3 km/s vesc) |
| Insolation Flux | 0.1169 S⊕ (~159 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 79.400 LY (24.332 pc) |