KELT-4 A b
Astrophysical Synthesis & Habitability Characterization
KELT-4 A b is a confirmed gas giant exoplanet orbiting the star KELT-4 A, located approximately 711.2 light-years (218.05 parsecs) from the Solar System. First announced in 2016 by KELT using the Transit detection technique (producing an estimated primary transit depth of 1.1863% across the stellar disk), this world measures 19.044 Earth radii (1.7 Jupiter radii) and has a measured mass of 286.683 Earth masses (0.9 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.23 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.79 g⊕ (7.75 m/s²), and an escape velocity of 43.4 km/s.
In its orbital architecture around KELT-4 A, KELT-4 A b completes one full revolution every 2.99 Earth days at a semi-major axis of 0.04317 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 157.1 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 1823 K (+1550°C / +2822°F) and receiving 1,840.00 S⊕ (~2,504,240 W/m²), KELT-4 A b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star KELT-4 A is classified as a warm F-type star of spectral type F with an effective photospheric temperature of 6,206 K, a radius of 1.603 R☉, a mass of 1.201 M☉, an estimated bolometric luminosity of 3.42 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.44 Gyr and a metallicity of [Fe/H] = -0.116 dex (metal-poor relative to the Sun). From Earth, KELT-4 A shines at apparent V-band magnitude 9.98 (accessible to binoculars and small amateur telescopes) 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: KELT · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | KELT-4 A |
| Spectral Type | F |
| Effective Temp (Teff) | 6,206 K |
| Stellar Radius | 1.6030 R☉ |
| Stellar Mass | 1.2010 M☉ |
| Bolometric Luminosity | 3.42 L☉ |
| Metallicity [Fe/H] | -0.116 dex |
| Stellar Age | 4.440 Gyr |
| Apparent Magnitude | V: 9.980 · G: 9.957 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.043170 AU |
| Orbital Period | 2.99 days |
| Mean Orbital Velocity | 157.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 83.1600° |
| Mean Bulk Density | 0.23 g/cm³ (43.4 km/s vesc) |
| Insolation Flux | 1840.0000 S⊕ (~2,504,240 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 711.200 LY (218.050 pc) |