GJ 317 b
Astrophysical Synthesis & Habitability Characterization
GJ 317 b is a confirmed gas giant exoplanet orbiting the star GJ 317, located approximately 49.6 light-years (15.2 parsecs) from the Solar System. First announced in 2007 by W. M. Keck Observatory 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 794.5 Earth masses (2.5 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.86 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.49 g⊕ (44.03 m/s²), and an escape velocity of 86.5 km/s.
In its orbital architecture around GJ 317, GJ 317 b completes one full revolution every 695.69 Earth days (1.9Julian years) at a semi-major axis of 1.138 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 17.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.0826 carries the world between 1.044 AU at periapsis and 1.232 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 100 K (-173°C / -279°F) and an incident flux of 0.02 S⊕ (~22 W/m²), surface water and volatile species on GJ 317 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star GJ 317 is classified as a low-mass red dwarf of spectral type M3.5 V with an effective photospheric temperature of 3,496 K, a radius of 0.403 R☉, a mass of 0.402 M☉, an estimated bolometric luminosity of 0.022 L☉. Stellar evolution modeling indicates an estimated stellar age of 5 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, GJ 317 shines at apparent V-band magnitude 12.4 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The GJ 317 system is a multi-planet architecture hosting 2 confirmed worlds, with GJ 317 b sharing its stellar neighborhood alongside GJ 317 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 317 |
| Spectral Type | M3.5 V |
| Effective Temp (Teff) | 3,496 K |
| Stellar Radius | 0.4030 R☉ |
| Stellar Mass | 0.4020 M☉ |
| Bolometric Luminosity | 0.022 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 5.000 Gyr |
| Apparent Magnitude | V: 12.400 · G: 10.754 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.138000 AU |
| Orbital Period | 695.69 days |
| Mean Orbital Velocity | 17.8 km/s |
| Orbital Eccentricity (e) | 0.08260 |
| Orbital Inclination (i) | 45.0000° |
| Mean Bulk Density | 1.86 g/cm³ (86.5 km/s vesc) |
| Insolation Flux | 0.0159 S⊕ (~22 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 49.600 LY (15.197 pc) |