Kepler-4 b
Astrophysical Synthesis & Habitability Characterization
Kepler-4 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-4, located approximately 1591.4 light-years (487.92 parsecs) from the Solar System. First announced in 2009 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0609% across the stellar disk), this world measures 4.002 Earth radii (0.36 Jupiter radii) and has a measured mass of 24.472 Earth masses. Combining its mass and radius yields a mean bulk density of 2.11 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.53 g⊕ (15 m/s²), and an escape velocity of 27.7 km/s.
In its orbital architecture around Kepler-4, Kepler-4 b completes one full revolution every 3.213 Earth days at a semi-major axis of 0.0456 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 154.4 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 1650 K (+1377°C / +2511°F) and receiving 1,245.43 S⊕ (~1,695,032 W/m²), Kepler-4 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-4 is classified as a stellar host with an effective photospheric temperature of 5,857 K, a radius of 1.487 R☉, a mass of 1.223 M☉, an estimated bolometric luminosity of 2.335 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.5 Gyr and a metallicity of [Fe/H] = 0.17 dex (metal-rich relative to the Sun). From Earth, Kepler-4 shines at apparent V-band magnitude 12.285 (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-4 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,857 K |
| Stellar Radius | 1.4870 R☉ |
| Stellar Mass | 1.2230 M☉ |
| Bolometric Luminosity | 2.335 L☉ |
| Metallicity [Fe/H] | 0.170 dex |
| Stellar Age | 4.500 Gyr |
| Apparent Magnitude | V: 12.285 · G: 12.158 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.045600 AU |
| Orbital Period | 3.213 days |
| Mean Orbital Velocity | 154.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7600° |
| Mean Bulk Density | 2.11 g/cm³ (27.7 km/s vesc) |
| Insolation Flux | 1245.4310 S⊕ (~1,695,032 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1591.400 LY (487.916 pc) |