HAT-P-8 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-8 b is a confirmed gas giant exoplanet orbiting the star HAT-P-8, located approximately 690 light-years (211.55 parsecs) from the Solar System. First announced in 2008 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.8398% across the stellar disk), this world measures 15.693 Earth radii (1.4 Jupiter radii) and has a measured mass of 406.822 Earth masses (1.28 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.58 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.65 g⊕ (16.18 m/s²), and an escape velocity of 57 km/s.
In its orbital architecture around HAT-P-8, HAT-P-8 b completes one full revolution every 3.076 Earth days at a semi-major axis of 0.04496 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 159 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1713 K (+1440°C / +2624°F) and receiving 1,519.96 S⊕ (~2,068,672 W/m²), HAT-P-8 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-8 is classified as a warm F-type star of spectral type F6 with an effective photospheric temperature of 6,200 K, a radius of 1.57 R☉, a mass of 1.27 M☉, an estimated bolometric luminosity of 3.268 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.4 Gyr and a metallicity of [Fe/H] = 0.01 dex (near-solar heavy-element abundance). From Earth, HAT-P-8 shines at apparent V-band magnitude 10.358 (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-8 |
| Spectral Type | F6 |
| Effective Temp (Teff) | 6,200 K |
| Stellar Radius | 1.5700 R☉ |
| Stellar Mass | 1.2700 M☉ |
| Bolometric Luminosity | 3.268 L☉ |
| Metallicity [Fe/H] | 0.010 dex |
| Stellar Age | 3.400 Gyr |
| Apparent Magnitude | V: 10.358 · G: 10.149 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.044960 AU |
| Orbital Period | 3.076 days |
| Mean Orbital Velocity | 159 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.8000° |
| Mean Bulk Density | 0.58 g/cm³ (57 km/s vesc) |
| Insolation Flux | 1519.9645 S⊕ (~2,068,672 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 690.000 LY (211.553 pc) |