HATS-8 b
Astrophysical Synthesis & Habitability Characterization
HATS-8 b is a confirmed gas giant exoplanet orbiting the star HATS-8, located approximately 2591.8 light-years (794.64 parsecs) from the Solar System. First announced in 2015 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 0.6823% across the stellar disk), this world measures 9.785 Earth radii (0.87 Jupiter radii) and has a measured mass of 43.861 Earth masses (0.14 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.26 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.46 g⊕ (4.51 m/s²), and an escape velocity of 23.7 km/s.
In its orbital architecture around HATS-8, HATS-8 b completes one full revolution every 3.584 Earth days at a semi-major axis of 0.04667 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 141.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.376, swinging from 0.0291 AU at periapsis out to 0.0642 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1324 K (+1051°C / +1924°F) and receiving 510.82 S⊕ (~695,225 W/m²), HATS-8 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-8 is classified as a stellar host with an effective photospheric temperature of 5,679 K, a radius of 1.086 R☉, a mass of 1.056 M☉, an estimated bolometric luminosity of 1.101 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.1 Gyr and a metallicity of [Fe/H] = 0.21 dex (metal-rich relative to the Sun). From Earth, HATS-8 shines at apparent V-band magnitude 14.512 (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-8 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,679 K |
| Stellar Radius | 1.0860 R☉ |
| Stellar Mass | 1.0560 M☉ |
| Bolometric Luminosity | 1.101 L☉ |
| Metallicity [Fe/H] | 0.210 dex |
| Stellar Age | 5.100 Gyr |
| Apparent Magnitude | V: 14.512 · G: 14.337 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.046670 AU |
| Orbital Period | 3.584 days |
| Mean Orbital Velocity | 141.7 km/s |
| Orbital Eccentricity (e) | 0.37600 |
| Orbital Inclination (i) | 87.8000° |
| Mean Bulk Density | 0.26 g/cm³ (23.7 km/s vesc) |
| Insolation Flux | 510.8195 S⊕ (~695,225 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2591.800 LY (794.637 pc) |