WASP-47 d
Astrophysical Synthesis & Habitability Characterization
WASP-47 d is a confirmed sub-neptune exoplanet orbiting the star WASP-47, located approximately 863.6 light-years (264.78 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0838% across the stellar disk), this world measures 3.65 Earth radii (0.33 Jupiter radii) and has a measured mass of 15.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.76 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.16 g⊕ (11.38 m/s²), and an escape velocity of 23.1 km/s.
In its orbital architecture around WASP-47, WASP-47 d completes one full revolution every 9.031 Earth days at a semi-major axis of 0.085 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 102.4 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.001 (ranging from 0.0849 AU at periapsis to 0.0851 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 885 K (+612°C / +1134°F) and receiving 145.00 S⊕ (~197,345 W/m²), WASP-47 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star WASP-47 is classified as a solar-type yellow star of spectral type G9 with an effective photospheric temperature of 5,565 K, a radius of 1.156 R☉, a mass of 1.058 M☉, an estimated bolometric luminosity of 1.15 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.5 Gyr and a metallicity of [Fe/H] = 0.43 dex (metal-rich relative to the Sun). From Earth, WASP-47 shines at apparent V-band magnitude 11.936 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The WASP-47 system is a multi-planet architecture hosting 4 confirmed worlds, with WASP-47 d sharing its stellar neighborhood alongside WASP-47 e, WASP-47 b, WASP-47 c.
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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | WASP-47 |
| Spectral Type | G9 |
| Effective Temp (Teff) | 5,565 K |
| Stellar Radius | 1.1560 R☉ |
| Stellar Mass | 1.0580 M☉ |
| Bolometric Luminosity | 1.15 L☉ |
| Metallicity [Fe/H] | 0.430 dex |
| Stellar Age | 6.500 Gyr |
| Apparent Magnitude | V: 11.936 · G: 11.789 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.085000 AU |
| Orbital Period | 9.031 days |
| Mean Orbital Velocity | 102.4 km/s |
| Orbital Eccentricity (e) | 0.00100 |
| Orbital Inclination (i) | 89.2300° |
| Mean Bulk Density | 1.76 g/cm³ (23.1 km/s vesc) |
| Insolation Flux | 145.0000 S⊕ (~197,345 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 863.600 LY (264.780 pc) |