GJ 581 b
Astrophysical Synthesis & Habitability Characterization
GJ 581 b is a confirmed sub-neptune exoplanet orbiting the star GJ 581, located approximately 20.5 light-years (6.3 parsecs) from the Solar System. First announced in 2005 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.79 Earth radii (0.43 Jupiter radii) and has a measured mass of 20.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.03 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.89 g⊕ (8.73 m/s²), and an escape velocity of 23.1 km/s.
In its orbital architecture around GJ 581, GJ 581 b completes one full revolution every 5.369 Earth days at a semi-major axis of 0.0399 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 80.9 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0342 (ranging from 0.0385 AU at periapsis to 0.0413 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 464 K (+191°C / +376°F) and receiving 7.77 S⊕ (~10,571 W/m²), GJ 581 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 581 is classified as a low-mass red dwarf of spectral type M3.0 V with an effective photospheric temperature of 3,500 K, a radius of 0.302 R☉, a mass of 0.295 M☉, an estimated bolometric luminosity of 0.012 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.3 Gyr and a metallicity of [Fe/H] = -0.08 dex (near-solar heavy-element abundance). From Earth, GJ 581 shines at apparent V-band magnitude 10.57 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The GJ 581 system is a multi-planet architecture hosting 3 confirmed worlds, with GJ 581 b sharing its stellar neighborhood alongside GJ 581 e, GJ 581 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 581 |
| Spectral Type | M3.0 V |
| Effective Temp (Teff) | 3,500 K |
| Stellar Radius | 0.3020 R☉ |
| Stellar Mass | 0.2950 M☉ |
| Bolometric Luminosity | 0.012 L☉ |
| Metallicity [Fe/H] | -0.080 dex |
| Stellar Age | 4.300 Gyr |
| Apparent Magnitude | V: 10.570 · G: 9.411 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.039900 AU |
| Orbital Period | 5.369 days |
| Mean Orbital Velocity | 80.9 km/s |
| Orbital Eccentricity (e) | 0.03420 |
| Orbital Inclination (i) | 47.0000° |
| Mean Bulk Density | 1.03 g/cm³ (23.1 km/s vesc) |
| Insolation Flux | 7.7669 S⊕ (~10,571 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 20.500 LY (6.298 pc) |