HD 187123 c
Astrophysical Synthesis & Habitability Characterization
HD 187123 c is a confirmed gas giant exoplanet orbiting the star HD 187123, located approximately 149.9 light-years (45.96 parsecs) from the Solar System. First announced in 2008 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 13.2 Earth radii (1.18 Jupiter radii) and has a measured mass of 912.168 Earth masses (2.87 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.19 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 5.24 g⊕ (51.39 m/s²), and an escape velocity of 93 km/s.
In its orbital architecture around HD 187123, HD 187123 c completes one full revolution every 3810 Earth days (10.43Julian years) at a semi-major axis of 4.89 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 14 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.252, swinging from 3.6577 AU at periapsis out to 6.1223 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 135 K (-138°C / -216°F) and an incident flux of 0.06 S⊕ (~76 W/m²), surface water and volatile species on HD 187123 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 187123 is classified as a solar-type yellow star of spectral type G3 V with an effective photospheric temperature of 5,790 K, a radius of 1.1504 R☉, a mass of 1.04 M☉, an estimated bolometric luminosity of 1.334 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.4 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, HD 187123 shines at apparent V-band magnitude 7.83 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 187123 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 187123 c sharing its stellar neighborhood alongside HD 187123 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 187123 |
| Spectral Type | G3 V |
| Effective Temp (Teff) | 5,790 K |
| Stellar Radius | 1.1504 R☉ |
| Stellar Mass | 1.0400 M☉ |
| Bolometric Luminosity | 1.334 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 7.400 Gyr |
| Apparent Magnitude | V: 7.830 · G: 7.673 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 4.890000 AU |
| Orbital Period | 3810 days |
| Mean Orbital Velocity | 14 km/s |
| Orbital Eccentricity (e) | 0.25200 |
| Orbital Inclination (i) | 137.2000° |
| Mean Bulk Density | 2.19 g/cm³ (93 km/s vesc) |
| Insolation Flux | 0.0560 S⊕ (~76 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 149.900 LY (45.955 pc) |