HATS-4 b
Astrophysical Synthesis & Habitability Characterization
HATS-4 b is a confirmed gas giant exoplanet orbiting the star HATS-4, located approximately 1358.3 light-years (416.46 parsecs) from the Solar System. First announced in 2014 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 1.284% across the stellar disk), this world measures 11.433 Earth radii (1.02 Jupiter radii) and has a measured mass of 420.471 Earth masses (1.32 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.55 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.22 g⊕ (31.58 m/s²), and an escape velocity of 67.8 km/s.
In its orbital architecture around HATS-4, HATS-4 b completes one full revolution every 2.517 Earth days at a semi-major axis of 0.0362 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 156.5 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.013 (ranging from 0.0357 AU at periapsis to 0.0367 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1315 K (+1042°C / +1908°F) and receiving 558.83 S⊕ (~760,565 W/m²), HATS-4 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-4 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,403 K, a radius of 0.925 R☉, a mass of 1.001 M☉, an estimated bolometric luminosity of 0.654 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.1 Gyr and a metallicity of [Fe/H] = 0.43 dex (metal-rich relative to the Sun). From Earth, HATS-4 shines at apparent V-band magnitude 13.516 (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-4 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,403 K |
| Stellar Radius | 0.9250 R☉ |
| Stellar Mass | 1.0010 M☉ |
| Bolometric Luminosity | 0.654 L☉ |
| Metallicity [Fe/H] | 0.430 dex |
| Stellar Age | 2.100 Gyr |
| Apparent Magnitude | V: 13.516 · G: 13.286 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.036200 AU |
| Orbital Period | 2.517 days |
| Mean Orbital Velocity | 156.5 km/s |
| Orbital Eccentricity (e) | 0.01300 |
| Orbital Inclination (i) | 88.5000° |
| Mean Bulk Density | 1.55 g/cm³ (67.8 km/s vesc) |
| Insolation Flux | 558.8280 S⊕ (~760,565 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1358.300 LY (416.459 pc) |