GJ 581 c
Astrophysical Synthesis & Habitability Characterization
GJ 581 c 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 2007 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.5 Earth radii and has a measured mass of 6.81 Earth masses. Combining its mass and radius yields a mean bulk density of 2.4 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.5 km/s.
In its orbital architecture around GJ 581, GJ 581 c completes one full revolution every 12.921 Earth days at a semi-major axis of 0.0718 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 60.5 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.032 (ranging from 0.0695 AU at periapsis to 0.0741 AU at apoapsis), the planet experiences minimal orbital distance variation.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.500 R⊕, GJ 581 c 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 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 c sharing its stellar neighborhood alongside GJ 581 e, GJ 581 b.
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) | 0.071800 AU |
| Orbital Period | 12.921 days |
| Mean Orbital Velocity | 60.5 km/s |
| Orbital Eccentricity (e) | 0.03200 |
| Orbital Inclination (i) | 47.0000° |
| Mean Bulk Density | 2.4 g/cm³ (18.5 km/s vesc) |
| Insolation Flux | 2.3985 S⊕ (~3,264 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 20.500 LY (6.298 pc) |