HAT-P-9 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-9 b is a confirmed gas giant exoplanet orbiting the star HAT-P-9, located approximately 1484.7 light-years (455.2 parsecs) from the Solar System. First announced in 2008 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.1446% across the stellar disk), this world measures 15.614 Earth radii (1.39 Jupiter radii) and has a measured mass of 238.055 Earth masses (0.75 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.34 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 43.7 km/s.
In its orbital architecture around HAT-P-9, HAT-P-9 b completes one full revolution every 3.923 Earth days at a semi-major axis of 0.05287 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 146.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.084 carries the world between 0.0484 AU at periapsis and 0.0573 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1540 K (+1267°C / +2313°F) and receiving 931.00 S⊕ (~1,267,091 W/m²), HAT-P-9 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-9 is classified as a warm F-type star of spectral type F7 with an effective photospheric temperature of 6,350 K, a radius of 1.338 R☉, a mass of 1.281 M☉, an estimated bolometric luminosity of 2.612 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.6 Gyr and a metallicity of [Fe/H] = 0.12 dex (metal-rich relative to the Sun). From Earth, HAT-P-9 shines at apparent V-band magnitude 12.344 (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: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HAT-P-9 |
| Spectral Type | F7 |
| Effective Temp (Teff) | 6,350 K |
| Stellar Radius | 1.3380 R☉ |
| Stellar Mass | 1.2810 M☉ |
| Bolometric Luminosity | 2.612 L☉ |
| Metallicity [Fe/H] | 0.120 dex |
| Stellar Age | 1.600 Gyr |
| Apparent Magnitude | V: 12.344 · G: 12.154 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.052870 AU |
| Orbital Period | 3.923 days |
| Mean Orbital Velocity | 146.6 km/s |
| Orbital Eccentricity (e) | 0.08400 |
| Orbital Inclination (i) | 86.4400° |
| Mean Bulk Density | 0.34 g/cm³ (43.7 km/s vesc) |
| Insolation Flux | 931.0000 S⊕ (~1,267,091 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1484.700 LY (455.203 pc) |