K2-228 b
Astrophysical Synthesis & Habitability Characterization
K2-228 b is a confirmed terrestrial exoplanet orbiting the star K2-228, located approximately 422.2 light-years (129.46 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0291% across the stellar disk), this world measures 1.21 Earth radii and has a measured mass of 1.92 Earth masses. Combining its mass and radius yields a mean bulk density of 5.98 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.31 g⊕ (12.85 m/s²), and an escape velocity of 14.1 km/s.
In its orbital architecture around K2-228, K2-228 b completes one full revolution every 2.698 Earth days at a semi-major axis of 0.0338 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 136.3 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 914 K (+641°C / +1186°F) and receiving 123.98 S⊕ (~168,737 W/m²), K2-228 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-228 is classified as a stellar host with an effective photospheric temperature of 4,715 K, a radius of 0.65 R☉, a mass of 0.71 M☉, an estimated bolometric luminosity of 0.187 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.25 dex (metal-poor relative to the Sun). From Earth, K2-228 shines at apparent V-band magnitude 13.028 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.
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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-228 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,715 K |
| Stellar Radius | 0.6500 R☉ |
| Stellar Mass | 0.7100 M☉ |
| Bolometric Luminosity | 0.187 L☉ |
| Metallicity [Fe/H] | -0.250 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.028 · G: 12.653 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.033800 AU |
| Orbital Period | 2.698 days |
| Mean Orbital Velocity | 136.3 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 87.4650° |
| Mean Bulk Density | 5.98 g/cm³ (14.1 km/s vesc) |
| Insolation Flux | 123.9803 S⊕ (~168,737 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 422.200 LY (129.460 pc) |