HAT-P-51 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-51 b is a confirmed gas giant exoplanet orbiting the star HAT-P-51, located approximately 1435.4 light-years (440.09 parsecs) from the Solar System. First announced in 2015 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.5489% across the stellar disk), this world measures 13.507 Earth radii (1.21 Jupiter radii) and has a measured mass of 97.573 Earth masses (0.31 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.22 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.53 g⊕ (5.2 m/s²), and an escape velocity of 30.1 km/s.
In its orbital architecture around HAT-P-51, HAT-P-51 b completes one full revolution every 4.218 Earth days at a semi-major axis of 0.05042 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 130 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.0469 AU at periapsis and 0.0539 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1168 K (+895°C / +1643°F) and receiving 310.00 S⊕ (~421,910 W/m²), HAT-P-51 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-51 is classified as a solar-type yellow star of spectral type G7 with an effective photospheric temperature of 5,453 K, a radius of 0.995 R☉, a mass of 0.961 M☉, an estimated bolometric luminosity of 0.785 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.1 Gyr and a metallicity of [Fe/H] = 0.302 dex (metal-rich relative to the Sun). From Earth, HAT-P-51 shines at apparent V-band magnitude 13.51 (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: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HAT-P-51 |
| Spectral Type | G7 |
| Effective Temp (Teff) | 5,453 K |
| Stellar Radius | 0.9950 R☉ |
| Stellar Mass | 0.9610 M☉ |
| Bolometric Luminosity | 0.785 L☉ |
| Metallicity [Fe/H] | 0.302 dex |
| Stellar Age | 8.100 Gyr |
| Apparent Magnitude | V: 13.510 · G: 13.285 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.050420 AU |
| Orbital Period | 4.218 days |
| Mean Orbital Velocity | 130 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 89.2800° |
| Mean Bulk Density | 0.22 g/cm³ (30.1 km/s vesc) |
| Insolation Flux | 310.0000 S⊕ (~421,910 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1435.400 LY (440.089 pc) |