KELT-18 b
Astrophysical Synthesis & Habitability Characterization
KELT-18 b is a confirmed gas giant exoplanet orbiting the star KELT-18, located approximately 1048.2 light-years (321.38 parsecs) from the Solar System. First announced in 2017 by KELT-North using the Transit detection technique (producing an estimated primary transit depth of 0.715% across the stellar disk), this world measures 17.598 Earth radii (1.57 Jupiter radii) and has a measured mass of 375.039 Earth masses (1.18 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.38 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.21 g⊕ (11.87 m/s²), and an escape velocity of 51.6 km/s.
In its orbital architecture around KELT-18, KELT-18 b completes one full revolution every 2.872 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 172.4 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 2085 K (+1812°C / +3294°F) and receiving 3,152.00 S⊕ (~4,289,872 W/m²), KELT-18 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star KELT-18 is classified as a warm F-type star of spectral type F4 V with an effective photospheric temperature of 6,670 K, a radius of 1.908 R☉, a mass of 1.524 M☉, an estimated bolometric luminosity of 6.465 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.9 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, KELT-18 shines at apparent V-band magnitude 10.16 (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-North · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | KELT-18 |
| Spectral Type | F4 V |
| Effective Temp (Teff) | 6,670 K |
| Stellar Radius | 1.9080 R☉ |
| Stellar Mass | 1.5240 M☉ |
| Bolometric Luminosity | 6.465 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 1.900 Gyr |
| Apparent Magnitude | V: 10.160 · G: 10.104 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.045500 AU |
| Orbital Period | 2.872 days |
| Mean Orbital Velocity | 172.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.8600° |
| Mean Bulk Density | 0.38 g/cm³ (51.6 km/s vesc) |
| Insolation Flux | 3152.0000 S⊕ (~4,289,872 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1048.200 LY (321.376 pc) |