GJ 328 c
Astrophysical Synthesis & Habitability Characterization
GJ 328 c is a confirmed sub-neptune exoplanet orbiting the star GJ 328, located approximately 66.9 light-years (20.53 parsecs) from the Solar System. First announced in 2023 by Roque de los Muchachos Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.91 Earth radii (0.44 Jupiter radii) and has a measured mass of 21.4 Earth masses. Combining its mass and radius yields a mean bulk density of 1 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 23.4 km/s.
In its orbital architecture around GJ 328, GJ 328 c completes one full revolution every 241.8 Earth days at a semi-major axis of 0.657 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 29.6 km/s (compared to Earth's 29.8 km/s).
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 4.910 R⊕, GJ 328 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 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 c sharing its stellar neighborhood alongside GJ 328 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: Roque de los Muchachos 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) | 0.657000 AU |
| Orbital Period | 241.8 days |
| Mean Orbital Velocity | 29.6 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1 g/cm³ (23.4 km/s vesc) |
| Insolation Flux | 0.1927 S⊕ (~262 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 66.900 LY (20.527 pc) |