KELT-8 b
Astrophysical Synthesis & Habitability Characterization
KELT-8 b is a confirmed gas giant exoplanet orbiting the star KELT-8, located approximately 644.4 light-years (197.57 parsecs) from the Solar System. First announced in 2015 by KELT using the Transit detection technique (producing an estimated primary transit depth of 1.3002% across the stellar disk), this world measures 18.159 Earth radii (1.62 Jupiter radii) and has a measured mass of 209.768 Earth masses (0.66 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.19 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.64 g⊕ (6.28 m/s²), and an escape velocity of 38 km/s.
In its orbital architecture around KELT-8, KELT-8 b completes one full revolution every 3.244 Earth days at a semi-major axis of 0.0455 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 152.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.04 (ranging from 0.0437 AU at periapsis to 0.0473 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1675 K (+1402°C / +2556°F) and receiving 983.31 S⊕ (~1,338,285 W/m²), KELT-8 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star KELT-8 is classified as a solar-type yellow star of spectral type G2 V with an effective photospheric temperature of 5,754 K, a radius of 1.46 R☉, a mass of 0.81 M☉, an estimated bolometric luminosity of 2.096 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.4 Gyr and a metallicity of [Fe/H] = 0.27 dex (metal-rich relative to the Sun). From Earth, KELT-8 shines at apparent V-band magnitude 10.845 (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: KELT · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | KELT-8 |
| Spectral Type | G2 V |
| Effective Temp (Teff) | 5,754 K |
| Stellar Radius | 1.4600 R☉ |
| Stellar Mass | 0.8100 M☉ |
| Bolometric Luminosity | 2.096 L☉ |
| Metallicity [Fe/H] | 0.270 dex |
| Stellar Age | 5.400 Gyr |
| Apparent Magnitude | V: 10.845 · G: 10.670 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.045500 AU |
| Orbital Period | 3.244 days |
| Mean Orbital Velocity | 152.6 km/s |
| Orbital Eccentricity (e) | 0.04000 |
| Orbital Inclination (i) | 82.6500° |
| Mean Bulk Density | 0.19 g/cm³ (38 km/s vesc) |
| Insolation Flux | 983.3098 S⊕ (~1,338,285 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 644.400 LY (197.572 pc) |