HATS-9 b
Astrophysical Synthesis & Habitability Characterization
HATS-9 b is a confirmed gas giant exoplanet orbiting the star HATS-9, located approximately 2083.2 light-years (638.7 parsecs) from the Solar System. First announced in 2015 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 0.6625% across the stellar disk), this world measures 13.85 Earth radii (1.24 Jupiter radii) and has a measured mass of 266.024 Earth masses (0.84 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.55 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.39 g⊕ (13.63 m/s²), and an escape velocity of 49 km/s.
In its orbital architecture around HATS-9, HATS-9 b completes one full revolution every 1.915 Earth days at a semi-major axis of 0.0312 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 177.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.075 carries the world between 0.0289 AU at periapsis and 0.0335 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1746 K (+1473°C / +2683°F) and receiving 2,292.08 S⊕ (~3,119,526 W/m²), HATS-9 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-9 is classified as a stellar host with an effective photospheric temperature of 5,599 K, a radius of 1.56 R☉, a mass of 1.1 M☉, an estimated bolometric luminosity of 2.146 L☉. Stellar evolution modeling indicates an estimated stellar age of 10.8 Gyr and a metallicity of [Fe/H] = 0.38 dex (metal-rich relative to the Sun). From Earth, HATS-9 shines at apparent V-band magnitude 13.256 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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: HATSouth · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HATS-9 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,599 K |
| Stellar Radius | 1.5600 R☉ |
| Stellar Mass | 1.1000 M☉ |
| Bolometric Luminosity | 2.146 L☉ |
| Metallicity [Fe/H] | 0.380 dex |
| Stellar Age | 10.800 Gyr |
| Apparent Magnitude | V: 13.256 · G: 13.098 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.031200 AU |
| Orbital Period | 1.915 days |
| Mean Orbital Velocity | 177.2 km/s |
| Orbital Eccentricity (e) | 0.07500 |
| Orbital Inclination (i) | 88.9400° |
| Mean Bulk Density | 0.55 g/cm³ (49 km/s vesc) |
| Insolation Flux | 2292.0839 S⊕ (~3,119,526 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2083.200 LY (638.700 pc) |