Kepler-328 c
Astrophysical Synthesis & Habitability Characterization
Kepler-328 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-328, located approximately 7218.5 light-years (2213.19 parsecs) from the Solar System. First announced in 2013 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.2181% across the stellar disk), this world measures 5.4 Earth radii (0.48 Jupiter radii) and has a measured mass of 39.4 Earth masses (0.12 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.38 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.35 g⊕ (13.24 m/s²), and an escape velocity of 30.2 km/s.
In its orbital architecture around Kepler-328, Kepler-328 c completes one full revolution every 71.312 Earth days at a semi-major axis of 0.354 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 54 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 475 K (+202°C / +396°F) and receiving 22.03 S⊕ (~29,976 W/m²), Kepler-328 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-328 is classified as a stellar host with an effective photospheric temperature of 6,064 K, a radius of 1.06 R☉, a mass of 1.15 M☉, an estimated bolometric luminosity of 1.363 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.57 Gyr and a metallicity of [Fe/H] = 0.08 dex (metal-rich relative to the Sun). From Earth, Kepler-328 shines at apparent V-band magnitude 15.794 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-328 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-328 c sharing its stellar neighborhood alongside Kepler-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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-328 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,064 K |
| Stellar Radius | 1.0600 R☉ |
| Stellar Mass | 1.1500 M☉ |
| Bolometric Luminosity | 1.363 L☉ |
| Metallicity [Fe/H] | 0.080 dex |
| Stellar Age | 2.570 Gyr |
| Apparent Magnitude | V: 15.794 · G: 15.604 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.354000 AU |
| Orbital Period | 71.312 days |
| Mean Orbital Velocity | 54 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9700° |
| Mean Bulk Density | 1.38 g/cm³ (30.2 km/s vesc) |
| Insolation Flux | 22.0250 S⊕ (~29,976 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 7218.500 LY (2213.190 pc) |