KELT-9 b
Astrophysical Synthesis & Habitability Characterization
KELT-9 b is a confirmed gas giant exoplanet orbiting the star KELT-9, located approximately 666.8 light-years (204.46 parsecs) from the Solar System. First announced in 2017 by KELT-North using the Transit detection technique (producing an estimated primary transit depth of 0.677% across the stellar disk), this world measures 21.701 Earth radii (1.94 Jupiter radii) and has a measured mass of 915.346 Earth masses (2.88 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.94 g⊕ (19.02 m/s²), and an escape velocity of 72.6 km/s.
In its orbital architecture around KELT-9, KELT-9 b completes one full revolution every 1.481 Earth days at a semi-major axis of 0.03368 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 247.4 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 3921 K (+3648°C / +6598°F) and receiving 44,900.00 S⊕ (~61,108,900 W/m²), KELT-9 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star KELT-9 is classified as a luminous A-type star of spectral type A with an effective photospheric temperature of 9,270 K, a radius of 2.418 R☉, a mass of 2.32 M☉, an estimated bolometric luminosity of 38.737 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.45 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, KELT-9 shines at apparent V-band magnitude 7.55 (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-North · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | KELT-9 |
| Spectral Type | A |
| Effective Temp (Teff) | 9,270 K |
| Stellar Radius | 2.4180 R☉ |
| Stellar Mass | 2.3200 M☉ |
| Bolometric Luminosity | 38.737 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 0.450 Gyr |
| Apparent Magnitude | V: 7.550 · G: 7.577 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.033680 AU |
| Orbital Period | 1.481 days |
| Mean Orbital Velocity | 247.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 86.7900° |
| Mean Bulk Density | 0.49 g/cm³ (72.6 km/s vesc) |
| Insolation Flux | 44900.0000 S⊕ (~61,108,900 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 666.800 LY (204.455 pc) |