Kepler-228 c
Astrophysical Synthesis & Habitability Characterization
Kepler-228 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-228, located approximately 5364 light-years (1644.61 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0596% across the stellar disk), this world measures 2.7 Earth radii and has a measured mass of 7.75 Earth masses. Combining its mass and radius yields a mean bulk density of 2.17 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.06 g⊕ (10.4 m/s²), and an escape velocity of 19 km/s.
In its orbital architecture around Kepler-228, Kepler-228 c completes one full revolution every 4.134 Earth days at a semi-major axis of 0.052 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 136.8 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 1160 K (+887°C / +1629°F) and receiving 457.32 S⊕ (~622,410 W/m²), Kepler-228 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-228 is classified as a stellar host with an effective photospheric temperature of 6,043 K, a radius of 1.014 R☉, a mass of 1.006 M☉, an estimated bolometric luminosity of 1.23 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.76 Gyr and a metallicity of [Fe/H] = 0.18 dex (metal-rich relative to the Sun). From Earth, Kepler-228 shines at apparent V-band magnitude 15.902 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-228 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-228 c sharing its stellar neighborhood alongside Kepler-228 b, Kepler-228 d.
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-228 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,043 K |
| Stellar Radius | 1.0140 R☉ |
| Stellar Mass | 1.0060 M☉ |
| Bolometric Luminosity | 1.23 L☉ |
| Metallicity [Fe/H] | 0.180 dex |
| Stellar Age | 6.760 Gyr |
| Apparent Magnitude | V: 15.902 · G: 15.704 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.052000 AU |
| Orbital Period | 4.134 days |
| Mean Orbital Velocity | 136.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 83.7200° |
| Mean Bulk Density | 2.17 g/cm³ (19 km/s vesc) |
| Insolation Flux | 457.3180 S⊕ (~622,410 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5364.000 LY (1644.610 pc) |