WASP-78 b
Astrophysical Synthesis & Habitability Characterization
WASP-78 b is a confirmed gas giant exoplanet orbiting the star WASP-78, located approximately 2460.1 light-years (754.26 parsecs) from the Solar System. First announced in 2012 by SuperWASP using the Transit detection technique (producing an estimated primary transit depth of 0.65% across the stellar disk), this world measures 21.633 Earth radii (1.93 Jupiter radii) and has a measured mass of 352.791 Earth masses (1.11 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.19 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.75 g⊕ (7.35 m/s²), and an escape velocity of 45.2 km/s.
In its orbital architecture around WASP-78, WASP-78 b completes one full revolution every 2.175 Earth days at a semi-major axis of 0.03488 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 174.5 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 2470 K (+2197°C / +3987°F) and receiving 4,812.62 S⊕ (~6,549,981 W/m²), WASP-78 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star WASP-78 is classified as a stellar host with an effective photospheric temperature of 6,100 K, a radius of 2.46 R☉, a mass of 1.87 M☉, an estimated bolometric luminosity of 7.518 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.8 Gyr and a metallicity of [Fe/H] = -0.35 dex (metal-poor relative to the Sun). From Earth, WASP-78 shines at apparent V-band magnitude 11.965 (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-78 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,100 K |
| Stellar Radius | 2.4600 R☉ |
| Stellar Mass | 1.8700 M☉ |
| Bolometric Luminosity | 7.518 L☉ |
| Metallicity [Fe/H] | -0.350 dex |
| Stellar Age | 2.800 Gyr |
| Apparent Magnitude | V: 11.965 · G: 12.188 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.034880 AU |
| Orbital Period | 2.175 days |
| Mean Orbital Velocity | 174.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 83.2000° |
| Mean Bulk Density | 0.19 g/cm³ (45.2 km/s vesc) |
| Insolation Flux | 4812.6238 S⊕ (~6,549,981 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2460.100 LY (754.258 pc) |