GJ 876 b
Astrophysical Synthesis & Habitability Characterization
GJ 876 b is a confirmed gas giant exoplanet orbiting the star GJ 876, located approximately 15.2 light-years (4.68 parsecs) from the Solar System. First announced in 1998 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 723.224 Earth masses (2.28 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.7 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.09 g⊕ (40.11 m/s²), and an escape velocity of 82.5 km/s.
In its orbital architecture around GJ 876, GJ 876 b completes one full revolution every 61.117 Earth days at a semi-major axis of 0.208317 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 37.1 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0324 (ranging from 0.2016 AU at periapsis to 0.2151 AU at apoapsis), the planet experiences minimal orbital distance variation.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.300 R⊕, GJ 876 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star GJ 876 is classified as a low-mass red dwarf of spectral type M2.5V with an effective photospheric temperature of 3,294 K, a radius of 0.3 R☉, a mass of 0.32 M☉, an estimated bolometric luminosity of 0.00951 L☉. Stellar evolution modeling indicates an estimated stellar age of 1 Gyr and a metallicity of [Fe/H] = 0.213 dex (metal-rich relative to the Sun). From Earth, GJ 876 shines at apparent V-band magnitude 10.16 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The GJ 876 system is a multi-planet architecture hosting 4 confirmed worlds, with GJ 876 b sharing its stellar neighborhood alongside GJ 876 d, GJ 876 c, GJ 876 e.
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 Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 876 |
| Spectral Type | M2.5V |
| Effective Temp (Teff) | 3,294 K |
| Stellar Radius | 0.3000 R☉ |
| Stellar Mass | 0.3200 M☉ |
| Bolometric Luminosity | 0.00951 L☉ |
| Metallicity [Fe/H] | 0.213 dex |
| Stellar Age | 1.000 Gyr |
| Apparent Magnitude | V: 10.160 · G: 8.875 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.208317 AU |
| Orbital Period | 61.117 days |
| Mean Orbital Velocity | 37.1 km/s |
| Orbital Eccentricity (e) | 0.03240 |
| Orbital Inclination (i) | 59.0000° |
| Mean Bulk Density | 1.7 g/cm³ (82.5 km/s vesc) |
| Insolation Flux | 0.2857 S⊕ (~389 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 15.200 LY (4.675 pc) |