WASP-81 b
Astrophysical Synthesis & Habitability Characterization
WASP-81 b is a confirmed gas giant exoplanet orbiting the star WASP-81, located approximately 1299.7 light-years (398.51 parsecs) from the Solar System. First announced in 2017 by Multiple Facilities using the Transit detection technique (producing an estimated primary transit depth of 1.3101% across the stellar disk), this world measures 16.018 Earth radii (1.43 Jupiter radii) and has a measured mass of 231.698 Earth masses (0.73 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.31 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.9 g⊕ (8.83 m/s²), and an escape velocity of 42.5 km/s.
In its orbital architecture around WASP-81, WASP-81 b completes one full revolution every 2.716 Earth days at a semi-major axis of 0.03908 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). Its moderate orbital eccentricity of e = 0.066 carries the world between 0.0365 AU at periapsis and 0.0417 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1623 K (+1350°C / +2462°F) and receiving 1,034.09 S⊕ (~1,407,398 W/m²), WASP-81 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star WASP-81 is classified as a stellar host with an effective photospheric temperature of 5,870 K, a radius of 1.283 R☉, a mass of 1.08 M☉, an estimated bolometric luminosity of 1.753 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.36 dex (metal-poor relative to the Sun). From Earth, WASP-81 shines at apparent V-band magnitude 12.469 (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: Multiple Facilities · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | WASP-81 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,870 K |
| Stellar Radius | 1.2830 R☉ |
| Stellar Mass | 1.0800 M☉ |
| Bolometric Luminosity | 1.753 L☉ |
| Metallicity [Fe/H] | -0.360 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.469 · G: 12.333 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.039080 AU |
| Orbital Period | 2.716 days |
| Mean Orbital Velocity | 156.5 km/s |
| Orbital Eccentricity (e) | 0.06600 |
| Orbital Inclination (i) | 88.6900° |
| Mean Bulk Density | 0.31 g/cm³ (42.5 km/s vesc) |
| Insolation Flux | 1034.0911 S⊕ (~1,407,398 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1299.700 LY (398.505 pc) |