HATS-31 b
Astrophysical Synthesis & Habitability Characterization
HATS-31 b is a confirmed gas giant exoplanet orbiting the star HATS-31, located approximately 2524.4 light-years (773.97 parsecs) from the Solar System. First announced in 2016 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 0.8123% across the stellar disk), this world measures 18.383 Earth radii (1.64 Jupiter radii) and has a measured mass of 279.69 Earth masses (0.88 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.25 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.83 g⊕ (8.14 m/s²), and an escape velocity of 43.6 km/s.
In its orbital architecture around HATS-31, HATS-31 b completes one full revolution every 3.378 Earth days at a semi-major axis of 0.0478 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 153.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.233 carries the world between 0.0367 AU at periapsis and 0.0589 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1823 K (+1550°C / +2822°F) and receiving 1,619.41 S⊕ (~2,204,012 W/m²), HATS-31 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-31 is classified as a stellar host with an effective photospheric temperature of 6,050 K, a radius of 1.87 R☉, a mass of 1.275 M☉, an estimated bolometric luminosity of 4.203 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.3 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, HATS-31 shines at apparent V-band magnitude 13.315 (faint and requiring research-grade or CCD telescopic photometry) 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: HATSouth · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HATS-31 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,050 K |
| Stellar Radius | 1.8700 R☉ |
| Stellar Mass | 1.2750 M☉ |
| Bolometric Luminosity | 4.203 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 4.300 Gyr |
| Apparent Magnitude | V: 13.315 · G: 12.961 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.047800 AU |
| Orbital Period | 3.378 days |
| Mean Orbital Velocity | 153.9 km/s |
| Orbital Eccentricity (e) | 0.23300 |
| Orbital Inclination (i) | 85.0000° |
| Mean Bulk Density | 0.25 g/cm³ (43.6 km/s vesc) |
| Insolation Flux | 1619.4060 S⊕ (~2,204,012 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2524.400 LY (773.974 pc) |