WASP-18 b
Astrophysical Synthesis & Habitability Characterization
WASP-18 b is a confirmed gas giant exoplanet orbiting the star WASP-18, located approximately 402.7 light-years (123.48 parsecs) from the Solar System. First announced in 2009 by SuperWASP using the Transit detection technique (producing an estimated primary transit depth of 0.9333% across the stellar disk), this world measures 13.899 Earth radii (1.24 Jupiter radii) and has a measured mass of 3241.85 Earth masses (10.2 Jupiter masses). Combining its mass and radius yields a mean bulk density of 6.66 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 16.78 g⊕ (164.56 m/s²), and an escape velocity of 170.8 km/s.
In its orbital architecture around WASP-18, WASP-18 b completes one full revolution every 0.941 Earth days at a semi-major axis of 0.02024 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 233.9 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0051 (ranging from 0.0201 AU at periapsis to 0.0203 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 2429 K (+2156°C / +3913°F) and receiving 5,805.00 S⊕ (~7,900,605 W/m²), WASP-18 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star WASP-18 is classified as a warm F-type star of spectral type F6 IV-V with an effective photospheric temperature of 6,432 K, a radius of 1.319 R☉, a mass of 1.294 M☉, an estimated bolometric luminosity of 2.672 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.57 Gyr and a metallicity of [Fe/H] = 0.107 dex (metal-rich relative to the Sun). From Earth, WASP-18 shines at apparent V-band magnitude 9.28 (accessible to binoculars and small amateur telescopes) 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-18 |
| Spectral Type | F6 IV-V |
| Effective Temp (Teff) | 6,432 K |
| Stellar Radius | 1.3190 R☉ |
| Stellar Mass | 1.2940 M☉ |
| Bolometric Luminosity | 2.672 L☉ |
| Metallicity [Fe/H] | 0.107 dex |
| Stellar Age | 1.570 Gyr |
| Apparent Magnitude | V: 9.280 · G: 9.166 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.020240 AU |
| Orbital Period | 0.941 days |
| Mean Orbital Velocity | 233.9 km/s |
| Orbital Eccentricity (e) | 0.00510 |
| Orbital Inclination (i) | 83.5000° |
| Mean Bulk Density | 6.66 g/cm³ (170.8 km/s vesc) |
| Insolation Flux | 5805.0000 S⊕ (~7,900,605 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 402.700 LY (123.483 pc) |