HD 159868 c
Astrophysical Synthesis & Habitability Characterization
HD 159868 c is a confirmed gas giant exoplanet orbiting the star HD 159868, located approximately 182.2 light-years (55.85 parsecs) from the Solar System. First announced in 2012 by Anglo-Australian Telescope using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14 Earth radii (1.25 Jupiter radii) and has a measured mass of 244.093 Earth masses (0.77 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.25 g⊕ (12.26 m/s²), and an escape velocity of 46.7 km/s.
In its orbital architecture around HD 159868, HD 159868 c completes one full revolution every 351 Earth days at a semi-major axis of 1.032 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 32 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.184 carries the world between 0.8421 AU at periapsis and 1.2219 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 383 K (+110°C / +230°F) and receiving 3.38 S⊕ (~4,594 W/m²), HD 159868 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 159868 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,534 K, a radius of 2.13 R☉, a mass of 1.19 M☉, an estimated bolometric luminosity of 3.818 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.57 Gyr and a metallicity of [Fe/H] = -0.08 dex (near-solar heavy-element abundance). From Earth, HD 159868 shines at apparent V-band magnitude 7.24 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 159868 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 159868 c sharing its stellar neighborhood alongside HD 159868 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: Anglo-Australian Telescope · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 159868 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,534 K |
| Stellar Radius | 2.1300 R☉ |
| Stellar Mass | 1.1900 M☉ |
| Bolometric Luminosity | 3.818 L☉ |
| Metallicity [Fe/H] | -0.080 dex |
| Stellar Age | 7.570 Gyr |
| Apparent Magnitude | V: 7.240 · G: 7.046 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.032000 AU |
| Orbital Period | 351 days |
| Mean Orbital Velocity | 32 km/s |
| Orbital Eccentricity (e) | 0.18400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.49 g/cm³ (46.7 km/s vesc) |
| Insolation Flux | 3.3758 S⊕ (~4,594 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 182.200 LY (55.850 pc) |