Kepler-228 d
Astrophysical Synthesis & Habitability Characterization
Kepler-228 d 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 0.1334% across the stellar disk), this world measures 4.04 Earth radii (0.36 Jupiter radii) and has a measured mass of 15.4 Earth masses. Combining its mass and radius yields a mean bulk density of 1.29 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 21.8 km/s.
In its orbital architecture around Kepler-228, Kepler-228 d completes one full revolution every 11.094 Earth days at a semi-major axis of 0.101 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 99 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 835 K (+562°C / +1044°F) and receiving 122.78 S⊕ (~167,101 W/m²), Kepler-228 d 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 d sharing its stellar neighborhood alongside Kepler-228 b, Kepler-228 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: 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) | 0.101000 AU |
| Orbital Period | 11.094 days |
| Mean Orbital Velocity | 99 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.1100° |
| Mean Bulk Density | 1.29 g/cm³ (21.8 km/s vesc) |
| Insolation Flux | 122.7780 S⊕ (~167,101 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5364.000 LY (1644.610 pc) |