Kepler-396 c
Astrophysical Synthesis & Habitability Characterization
Kepler-396 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-396, located approximately 729.8 light-years (223.76 parsecs) from the Solar System. First announced in 2013 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.2101% across the stellar disk), this world measures 5.3 Earth radii (0.47 Jupiter radii) and has a measured mass of 17.9 Earth masses. Combining its mass and radius yields a mean bulk density of 0.66 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.64 g⊕ (6.28 m/s²), and an escape velocity of 20.6 km/s.
In its orbital architecture around Kepler-396, Kepler-396 c completes one full revolution every 88.505 Earth days at a semi-major axis of 0.38946 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 47.9 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 390 K (+117°C / +243°F) and receiving 5.24 S⊕ (~7,137 W/m²), Kepler-396 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-396 is classified as a stellar host with an effective photospheric temperature of 5,656 K, a radius of 1.06 R☉, a mass of 0.85 M☉, an estimated bolometric luminosity of 1.032 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.62 Gyr and a metallicity of [Fe/H] = 0.156 dex (metal-rich relative to the Sun). From Earth, Kepler-396 shines at apparent V-band magnitude 12.259 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-396 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-396 c sharing its stellar neighborhood alongside Kepler-396 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-396 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,656 K |
| Stellar Radius | 1.0600 R☉ |
| Stellar Mass | 0.8500 M☉ |
| Bolometric Luminosity | 1.032 L☉ |
| Metallicity [Fe/H] | 0.156 dex |
| Stellar Age | 0.620 Gyr |
| Apparent Magnitude | V: 12.259 · G: 11.829 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.389460 AU |
| Orbital Period | 88.505 days |
| Mean Orbital Velocity | 47.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 90.0000° |
| Mean Bulk Density | 0.66 g/cm³ (20.6 km/s vesc) |
| Insolation Flux | 5.2440 S⊕ (~7,137 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 729.800 LY (223.757 pc) |