HAT-P-4 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-4 b is a confirmed gas giant exoplanet orbiting the star HAT-P-4, located approximately 1045.2 light-years (320.45 parsecs) from the Solar System. First announced in 2007 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.6729% across the stellar disk), this world measures 14.28 Earth radii (1.27 Jupiter radii) and has a measured mass of 213.255 Earth masses (0.67 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.4 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 43.2 km/s.
In its orbital architecture around HAT-P-4, HAT-P-4 b completes one full revolution every 3.057 Earth days at a semi-major axis of 0.04438 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 158 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 1686 K (+1413°C / +2575°F) and receiving 1,438.00 S⊕ (~1,957,118 W/m²), HAT-P-4 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-4 is classified as a warm F-type star of spectral type F with an effective photospheric temperature of 5,860 K, a radius of 1.596 R☉, a mass of 1.248 M☉, an estimated bolometric luminosity of 2.695 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.9 Gyr and a metallicity of [Fe/H] = 0.24 dex (metal-rich relative to the Sun). From Earth, HAT-P-4 shines at apparent V-band magnitude 11.118 (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-4 |
| Spectral Type | F |
| Effective Temp (Teff) | 5,860 K |
| Stellar Radius | 1.5960 R☉ |
| Stellar Mass | 1.2480 M☉ |
| Bolometric Luminosity | 2.695 L☉ |
| Metallicity [Fe/H] | 0.240 dex |
| Stellar Age | 3.900 Gyr |
| Apparent Magnitude | V: 11.118 · G: 11.063 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.044380 AU |
| Orbital Period | 3.057 days |
| Mean Orbital Velocity | 158 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9100° |
| Mean Bulk Density | 0.4 g/cm³ (43.2 km/s vesc) |
| Insolation Flux | 1438.0000 S⊕ (~1,957,118 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1045.200 LY (320.451 pc) |