HD 133131 A b
Astrophysical Synthesis & Habitability Characterization
HD 133131 A b is a confirmed gas giant exoplanet orbiting the star HD 133131 A, located approximately 167.9 light-years (51.47 parsecs) from the Solar System. First announced in 2016 by Las Campanas Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 451.319 Earth masses (1.42 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.99 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.44 g⊕ (23.93 m/s²), and an escape velocity of 64.4 km/s.
In its orbital architecture around HD 133131 A, HD 133131 A b completes one full revolution every 649 Earth days (1.78Julian years) at a semi-major axis of 1.44 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 24.1 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.33, swinging from 0.9648 AU at periapsis out to 1.9152 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.600 R⊕, HD 133131 A 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 133131 A is classified as a solar-type yellow star of spectral type G2 V with an effective photospheric temperature of 5,799 K, a radius of 0.955 R☉, a mass of 0.95 M☉, an estimated bolometric luminosity of 0.925 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.7 Gyr and a metallicity of [Fe/H] = -0.306 dex (metal-poor relative to the Sun). From Earth, HD 133131 A shines at apparent V-band magnitude 7.66 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 133131 A system is a multi-planet architecture hosting 2 confirmed worlds, with HD 133131 A b sharing its stellar neighborhood alongside HD 133131 A 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: Las Campanas Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 133131 A |
| Spectral Type | G2 V |
| Effective Temp (Teff) | 5,799 K |
| Stellar Radius | 0.9550 R☉ |
| Stellar Mass | 0.9500 M☉ |
| Bolometric Luminosity | 0.925 L☉ |
| Metallicity [Fe/H] | -0.306 dex |
| Stellar Age | 9.700 Gyr |
| Apparent Magnitude | V: 7.660 · G: 8.275 |
| System Architecture | 2 Stars, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.440000 AU |
| Orbital Period | 649 days |
| Mean Orbital Velocity | 24.1 km/s |
| Orbital Eccentricity (e) | 0.33000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.99 g/cm³ (64.4 km/s vesc) |
| Insolation Flux | 0.4642 S⊕ (~632 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 167.900 LY (51.474 pc) |