HD 159868 b
Astrophysical Synthesis & Habitability Characterization
HD 159868 b 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 2006 by Anglo-Australian Telescope using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 704.947 Earth masses (2.22 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.65 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.99 g⊕ (39.13 m/s²), and an escape velocity of 81.4 km/s.
In its orbital architecture around HD 159868, HD 159868 b completes one full revolution every 1184.1 Earth days (3.24Julian years) at a semi-major axis of 2.32 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 21.3 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.024 (ranging from 2.2643 AU at periapsis to 2.3757 AU at apoapsis), the planet experiences minimal orbital distance variation.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.300 R⊕, HD 159868 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
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 b sharing its stellar neighborhood alongside HD 159868 c.
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) | 2.320000 AU |
| Orbital Period | 1184.1 days |
| Mean Orbital Velocity | 21.3 km/s |
| Orbital Eccentricity (e) | 0.02400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.65 g/cm³ (81.4 km/s vesc) |
| Insolation Flux | 0.6680 S⊕ (~909 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 182.200 LY (55.850 pc) |