HAT-P-31 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-31 b is a confirmed gas giant exoplanet orbiting the star HAT-P-31, located approximately 1122.1 light-years (344.05 parsecs) from the Solar System. First announced in 2011 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.6494% across the stellar disk), this world measures 12.218 Earth radii (1.09 Jupiter radii) and has a measured mass of 721.474 Earth masses (2.27 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.18 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 4.83 g⊕ (47.37 m/s²), and an escape velocity of 86 km/s.
In its orbital architecture around HAT-P-31, HAT-P-31 b completes one full revolution every 5.005 Earth days at a semi-major axis of 0.061 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 132.6 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 0.0458 AU at periapsis out to 0.0763 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1450 K (+1177°C / +2151°F) and receiving 746.90 S⊕ (~1,016,534 W/m²), HAT-P-31 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-31 is classified as a stellar host with an effective photospheric temperature of 6,065 K, a radius of 1.39 R☉, a mass of 1.31 M☉, an estimated bolometric luminosity of 2.346 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.17 Gyr and a metallicity of [Fe/H] = 0.15 dex (metal-rich relative to the Sun). From Earth, HAT-P-31 shines at apparent V-band magnitude 11.667 (faint and requiring research-grade or CCD telescopic photometry) 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: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HAT-P-31 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,065 K |
| Stellar Radius | 1.3900 R☉ |
| Stellar Mass | 1.3100 M☉ |
| Bolometric Luminosity | 2.346 L☉ |
| Metallicity [Fe/H] | 0.150 dex |
| Stellar Age | 3.170 Gyr |
| Apparent Magnitude | V: 11.667 · G: 11.450 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.061000 AU |
| Orbital Period | 5.005 days |
| Mean Orbital Velocity | 132.6 km/s |
| Orbital Eccentricity (e) | 0.25000 |
| Orbital Inclination (i) | 87.1000° |
| Mean Bulk Density | 2.18 g/cm³ (86 km/s vesc) |
| Insolation Flux | 746.9025 S⊕ (~1,016,534 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1122.100 LY (344.050 pc) |