HD 171238 b
Astrophysical Synthesis & Habitability Characterization
HD 171238 b is a confirmed gas giant exoplanet orbiting the star HD 171238, located approximately 146.2 light-years (44.81 parsecs) from the Solar System. First announced in 2009 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.5 Earth radii (1.12 Jupiter radii) and has a measured mass of 2796.89 Earth masses (8.8 Jupiter masses). Combining its mass and radius yields a mean bulk density of 7.9 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 17.9 g⊕ (175.54 m/s²), and an escape velocity of 167.3 km/s.
In its orbital architecture around HD 171238, HD 171238 b completes one full revolution every 1515 Earth days (4.15Julian years) at a semi-major axis of 2.518 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 18.1 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.358, swinging from 1.6166 AU at periapsis out to 3.4194 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 167 K (-106°C / -159°F) and an incident flux of 0.10 S⊕ (~135 W/m²), surface water and volatile species on HD 171238 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 171238 is classified as a solar-type yellow star of spectral type G8 V with an effective photospheric temperature of 5,467 K, a radius of 1.01 R☉, a mass of 0.92 M☉, an estimated bolometric luminosity of 0.818 L☉. Stellar evolution modeling indicates an estimated stellar age of 7 Gyr and a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, HD 171238 shines at apparent V-band magnitude 8.61 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere.
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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 171238 |
| Spectral Type | G8 V |
| Effective Temp (Teff) | 5,467 K |
| Stellar Radius | 1.0100 R☉ |
| Stellar Mass | 0.9200 M☉ |
| Bolometric Luminosity | 0.818 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | 7.000 Gyr |
| Apparent Magnitude | V: 8.610 · G: 8.411 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.518000 AU |
| Orbital Period | 1515 days |
| Mean Orbital Velocity | 18.1 km/s |
| Orbital Eccentricity (e) | 0.35800 |
| Orbital Inclination (i) | 19.1000° |
| Mean Bulk Density | 7.9 g/cm³ (167.3 km/s vesc) |
| Insolation Flux | 0.0989 S⊕ (~135 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 146.200 LY (44.811 pc) |