51 Peg b
Astrophysical Synthesis & Habitability Characterization
51 Peg b is a confirmed gas giant exoplanet orbiting the star 51 Peg, located approximately 50.4 light-years (15.46 parsecs) from the Solar System. First announced in 1995 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.1 Earth radii (1.26 Jupiter radii) and has a measured mass of 193.875 Earth masses (0.61 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.38 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 41.5 km/s.
In its orbital architecture around 51 Peg, 51 Peg b completes one full revolution every 4.231 Earth days at a semi-major axis of 0.052 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 133.7 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0063 (ranging from 0.0517 AU at periapsis to 0.0523 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1329 K (+1056°C / +1933°F) and receiving 506.18 S⊕ (~688,908 W/m²), 51 Peg b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star 51 Peg is classified as a solar-type yellow star of spectral type G5V with an effective photospheric temperature of 5,761 K, a radius of 1.19 R☉, a mass of 1.07 M☉, an estimated bolometric luminosity of 1.4 L☉. Stellar evolution modeling indicates an estimated stellar age of 10 Gyr and a metallicity of [Fe/H] = 0.206 dex (metal-rich relative to the Sun). From Earth, 51 Peg shines at apparent V-band magnitude 5.453 (visible to the unaided human eye under dark skies) 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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | 51 Peg |
| Spectral Type | G5V |
| Effective Temp (Teff) | 5,761 K |
| Stellar Radius | 1.1900 R☉ |
| Stellar Mass | 1.0700 M☉ |
| Bolometric Luminosity | 1.4 L☉ |
| Metallicity [Fe/H] | 0.206 dex |
| Stellar Age | 10.000 Gyr |
| Apparent Magnitude | V: 5.453 · G: 5.286 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.052000 AU |
| Orbital Period | 4.231 days |
| Mean Orbital Velocity | 133.7 km/s |
| Orbital Eccentricity (e) | 0.00630 |
| Orbital Inclination (i) | 49.8000° |
| Mean Bulk Density | 0.38 g/cm³ (41.5 km/s vesc) |
| Insolation Flux | 506.1775 S⊕ (~688,908 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 50.400 LY (15.461 pc) |