GJ 328 b
Astrophysical Synthesis & Habitability Characterization
GJ 328 b is a confirmed gas giant exoplanet orbiting the star GJ 328, located approximately 66.9 light-years (20.53 parsecs) from the Solar System. First announced in 2013 by McDonald 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 797.749 Earth masses (2.51 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.87 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.51 g⊕ (44.23 m/s²), and an escape velocity of 86.6 km/s.
In its orbital architecture around GJ 328, GJ 328 b completes one full revolution every 3771 Earth days (10.32Julian years) at a semi-major axis of 4.11 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 11.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.227 carries the world between 3.177 AU at periapsis and 5.043 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 74 K (-199°C / -326°F) and an incident flux of 0.00 S⊕ (~7 W/m²), surface water and volatile species on GJ 328 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star GJ 328 is classified as a low-mass red dwarf of spectral type M0.0 with an effective photospheric temperature of 3,897 K, a radius of 0.63 R☉, a mass of 0.65 M☉, an estimated bolometric luminosity of 0.082 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.06 dex (near-solar heavy-element abundance). From Earth, GJ 328 shines at apparent V-band magnitude 9.99 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The GJ 328 system is a multi-planet architecture hosting 2 confirmed worlds, with GJ 328 b sharing its stellar neighborhood alongside GJ 328 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: McDonald Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 328 |
| Spectral Type | M0.0 |
| Effective Temp (Teff) | 3,897 K |
| Stellar Radius | 0.6300 R☉ |
| Stellar Mass | 0.6500 M☉ |
| Bolometric Luminosity | 0.082 L☉ |
| Metallicity [Fe/H] | -0.060 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.990 · G: 9.286 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 4.110000 AU |
| Orbital Period | 3771 days |
| Mean Orbital Velocity | 11.9 km/s |
| Orbital Eccentricity (e) | 0.22700 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.87 g/cm³ (86.6 km/s vesc) |
| Insolation Flux | 0.0049 S⊕ (~7 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 66.900 LY (20.527 pc) |