HD 13931 b
Astrophysical Synthesis & Habitability Characterization
HD 13931 b is a confirmed gas giant exoplanet orbiting the star HD 13931, located approximately 154.6 light-years (47.4 parsecs) from the Solar System. First announced in 2009 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 889.92 Earth masses (2.8 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.13 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 5.11 g⊕ (50.11 m/s²), and an escape velocity of 91.8 km/s.
In its orbital architecture around HD 13931, HD 13931 b completes one full revolution every 4218 Earth days (11.55Julian years) at a semi-major axis of 5.15 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 13.3 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.02 (ranging from 5.047 AU at periapsis to 5.253 AU at apoapsis), the planet experiences minimal orbital distance variation.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 139 K (-134°C / -209°F) and an incident flux of 0.06 S⊕ (~81 W/m²), surface water and volatile species on HD 13931 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 13931 is classified as a solar-type yellow star of spectral type G0 with an effective photospheric temperature of 5,867 K, a radius of 1.25 R☉, a mass of 1.3 M☉, an estimated bolometric luminosity of 1.661 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.4 Gyr and a metallicity of [Fe/H] = 0.05 dex (near-solar heavy-element abundance). From Earth, HD 13931 shines at apparent V-band magnitude 7.61 (accessible to binoculars and small amateur telescopes) in the Northern 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 13931 |
| Spectral Type | G0 |
| Effective Temp (Teff) | 5,867 K |
| Stellar Radius | 1.2500 R☉ |
| Stellar Mass | 1.3000 M☉ |
| Bolometric Luminosity | 1.661 L☉ |
| Metallicity [Fe/H] | 0.050 dex |
| Stellar Age | 8.400 Gyr |
| Apparent Magnitude | V: 7.610 · G: 7.455 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 5.150000 AU |
| Orbital Period | 4218 days |
| Mean Orbital Velocity | 13.3 km/s |
| Orbital Eccentricity (e) | 0.02000 |
| Orbital Inclination (i) | 43.0000° |
| Mean Bulk Density | 2.13 g/cm³ (91.8 km/s vesc) |
| Insolation Flux | 0.0592 S⊕ (~81 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 154.600 LY (47.396 pc) |