WASP-138 b

Astrophysical Synthesis & Habitability Characterization

WASP-138 b is a confirmed gas giant exoplanet orbiting the star WASP-138, located approximately 1351 light-years (414.23 parsecs) from the Solar System. First announced in 2016 by SuperWASP using the Transit detection technique (producing an estimated primary transit depth of 0.6784% across the stellar disk), this world measures 12.218 Earth radii (1.09 Jupiter radii) and has a measured mass of 387.753 Earth masses (1.22 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.17 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.6 g⊕ (25.5 m/s²), and an escape velocity of 63 km/s.

In its orbital architecture around WASP-138, WASP-138 b completes one full revolution every 3.634 Earth days at a semi-major axis of 0.0494 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 147.9 km/s (compared to Earth's 29.8 km/s).

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1590 K (+1317°C / +2403°F) and receiving 1,133.73 S⊕ (~1,543,007 W/m²), WASP-138 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star WASP-138 is classified as a stellar host with an effective photospheric temperature of 6,272 K, a radius of 1.36 R☉, a mass of 1.22 M☉, an estimated bolometric luminosity of 2.568 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.44 Gyr and a metallicity of [Fe/H] = -0.09 dex (near-solar heavy-element abundance). From Earth, WASP-138 shines at apparent V-band magnitude 11.796 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.

Discovery Facility: SuperWASP · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).