HD 156668 b
Astrophysical Synthesis & Habitability Characterization
HD 156668 b is a confirmed super-earth exoplanet orbiting the star HD 156668, located approximately 79.4 light-years (24.33 parsecs) from the Solar System. First announced in 2010 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 1.87 Earth radii and has a measured mass of 4.15 Earth masses. Combining its mass and radius yields a mean bulk density of 3.5 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.19 g⊕ (11.67 m/s²), and an escape velocity of 16.7 km/s.
In its orbital architecture around HD 156668, HD 156668 b completes one full revolution every 4.646 Earth days at a semi-major axis of 0.05 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 117.1 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 887 K (+614°C / +1137°F) and receiving 679.30 S⊕ (~924,524 W/m²), HD 156668 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 156668 is classified as an orange K-type star of spectral type K2 with an effective photospheric temperature of 4,850 K, a radius of 0.72 R☉, a mass of 0.772 M☉, an estimated bolometric luminosity of 0.257 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.6 Gyr and a metallicity of [Fe/H] = 0.05 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 b sharing its stellar neighborhood alongside HD 156668 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 156668 |
| Spectral Type | K2 |
| Effective Temp (Teff) | 4,850 K |
| Stellar Radius | 0.7200 R☉ |
| Stellar Mass | 0.7720 M☉ |
| Bolometric Luminosity | 0.257 L☉ |
| Metallicity [Fe/H] | 0.050 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) | 0.050000 AU |
| Orbital Period | 4.646 days |
| Mean Orbital Velocity | 117.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 3.5 g/cm³ (16.7 km/s vesc) |
| Insolation Flux | 679.2975 S⊕ (~924,524 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 79.400 LY (24.332 pc) |