HATS-15 b
Astrophysical Synthesis & Habitability Characterization
HATS-15 b is a confirmed gas giant exoplanet orbiting the star HATS-15, located approximately 3716.7 light-years (1139.55 parsecs) from the Solar System. First announced in 2016 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 1.5168% across the stellar disk), this world measures 12.386 Earth radii (1.11 Jupiter radii) and has a measured mass of 689.691 Earth masses (2.17 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 4.5 g⊕ (44.13 m/s²), and an escape velocity of 83.5 km/s.
In its orbital architecture around HATS-15, HATS-15 b completes one full revolution every 1.747 Earth days at a semi-major axis of 0.02712 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 168.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.126 carries the world between 0.0237 AU at periapsis and 0.0305 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1505 K (+1232°C / +2250°F) and receiving 2,201.34 S⊕ (~2,996,019 W/m²), HATS-15 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-15 is classified as a solar-type yellow star of spectral type G9 V with an effective photospheric temperature of 5,311 K, a radius of 0.922 R☉, a mass of 0.871 M☉, an estimated bolometric luminosity of 0.607 L☉. Stellar evolution modeling indicates an estimated stellar age of 11 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, HATS-15 shines at apparent V-band magnitude 14.909 (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-15 |
| Spectral Type | G9 V |
| Effective Temp (Teff) | 5,311 K |
| Stellar Radius | 0.9220 R☉ |
| Stellar Mass | 0.8710 M☉ |
| Bolometric Luminosity | 0.607 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 11.000 Gyr |
| Apparent Magnitude | V: 14.909 · G: 14.647 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.027120 AU |
| Orbital Period | 1.747 days |
| Mean Orbital Velocity | 168.8 km/s |
| Orbital Eccentricity (e) | 0.12600 |
| Orbital Inclination (i) | 87.1300° |
| Mean Bulk Density | 2 g/cm³ (83.5 km/s vesc) |
| Insolation Flux | 2201.3363 S⊕ (~2,996,019 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3716.700 LY (1139.550 pc) |