WASP-4 b
Astrophysical Synthesis & Habitability Characterization
WASP-4 b is a confirmed gas giant exoplanet orbiting the star WASP-4, located approximately 871.5 light-years (267.21 parsecs) from the Solar System. First announced in 2007 by SuperWASP using the Transit detection technique (producing an estimated primary transit depth of 2.3105% across the stellar disk), this world measures 15.121 Earth radii (1.35 Jupiter radii) and has a measured mass of 381.394 Earth masses (1.2 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.61 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.67 g⊕ (16.38 m/s²), and an escape velocity of 56.2 km/s.
In its orbital architecture around WASP-4, WASP-4 b completes one full revolution every 1.338 Earth days at a semi-major axis of 0.02261 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 183.8 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0053 (ranging from 0.0225 AU at periapsis to 0.0227 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1653 K (+1380°C / +2516°F) and receiving 1,188.62 S⊕ (~1,617,714 W/m²), WASP-4 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star WASP-4 is classified as a solar-type yellow star of spectral type G8 with an effective photospheric temperature of 5,436 K, a radius of 0.912 R☉, a mass of 0.899 M☉, an estimated bolometric luminosity of 0.652 L☉. Stellar evolution modeling indicates an estimated stellar age of 7 Gyr and a metallicity of [Fe/H] = -0.05 dex (near-solar heavy-element abundance). From Earth, WASP-4 shines at apparent V-band magnitude 12.483 (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: SuperWASP · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | WASP-4 |
| Spectral Type | G8 |
| Effective Temp (Teff) | 5,436 K |
| Stellar Radius | 0.9120 R☉ |
| Stellar Mass | 0.8990 M☉ |
| Bolometric Luminosity | 0.652 L☉ |
| Metallicity [Fe/H] | -0.050 dex |
| Stellar Age | 7.000 Gyr |
| Apparent Magnitude | V: 12.483 · G: 12.316 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.022610 AU |
| Orbital Period | 1.338 days |
| Mean Orbital Velocity | 183.8 km/s |
| Orbital Eccentricity (e) | 0.00530 |
| Orbital Inclination (i) | 88.0500° |
| Mean Bulk Density | 0.61 g/cm³ (56.2 km/s vesc) |
| Insolation Flux | 1188.6219 S⊕ (~1,617,714 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 871.500 LY (267.206 pc) |