Kepler-428 b
Astrophysical Synthesis & Habitability Characterization
Kepler-428 b is a confirmed gas giant exoplanet orbiting the star Kepler-428, located approximately 2238.4 light-years (686.28 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 1.926% across the stellar disk), this world measures 12.11 Earth radii (1.08 Jupiter radii) and has a measured mass of 403.63 Earth masses (1.27 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.25 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.75 g⊕ (26.97 m/s²), and an escape velocity of 64.6 km/s.
In its orbital architecture around Kepler-428, Kepler-428 b completes one full revolution every 3.526 Earth days at a semi-major axis of 0.0433 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 133.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.22 carries the world between 0.0338 AU at periapsis and 0.0528 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1070 K (+797°C / +1467°F) and receiving 195.09 S⊕ (~265,515 W/m²), Kepler-428 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-428 is classified as an orange K-type star of spectral type K1 V with an effective photospheric temperature of 5,150 K, a radius of 0.8 R☉, a mass of 0.87 M☉, an estimated bolometric luminosity of 0.404 L☉. Stellar evolution modeling indicates an estimated stellar age of 5 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, Kepler-428 shines at apparent V-band magnitude 15.362 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-428 |
| Spectral Type | K1 V |
| Effective Temp (Teff) | 5,150 K |
| Stellar Radius | 0.8000 R☉ |
| Stellar Mass | 0.8700 M☉ |
| Bolometric Luminosity | 0.404 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 5.000 Gyr |
| Apparent Magnitude | V: 15.362 · G: 15.222 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.043300 AU |
| Orbital Period | 3.526 days |
| Mean Orbital Velocity | 133.6 km/s |
| Orbital Eccentricity (e) | 0.22000 |
| Orbital Inclination (i) | 89.3600° |
| Mean Bulk Density | 1.25 g/cm³ (64.6 km/s vesc) |
| Insolation Flux | 195.0880 S⊕ (~265,515 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2238.400 LY (686.284 pc) |