HATS-39 b
Astrophysical Synthesis & Habitability Characterization
HATS-39 b is a confirmed gas giant exoplanet orbiting the star HATS-39, located approximately 2865.3 light-years (878.52 parsecs) from the Solar System. First announced in 2018 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 0.9906% across the stellar disk), this world measures 17.598 Earth radii (1.57 Jupiter radii) and has a measured mass of 200.233 Earth masses (0.63 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.2 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.65 g⊕ (6.37 m/s²), and an escape velocity of 37.7 km/s.
In its orbital architecture around HATS-39, HATS-39 b completes one full revolution every 4.578 Earth days at a semi-major axis of 0.06007 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 142.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.275, swinging from 0.0436 AU at periapsis out to 0.0766 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1645 K (+1372°C / +2502°F) and receiving 1,547.10 S⊕ (~2,105,605 W/m²), HATS-39 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-39 is classified as a stellar host with an effective photospheric temperature of 6,572 K, a radius of 1.621 R☉, a mass of 1.379 M☉, an estimated bolometric luminosity of 4.398 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.06 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, HATS-39 shines at apparent V-band magnitude 12.745 (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-39 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,572 K |
| Stellar Radius | 1.6210 R☉ |
| Stellar Mass | 1.3790 M☉ |
| Bolometric Luminosity | 4.398 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 2.060 Gyr |
| Apparent Magnitude | V: 12.745 · G: 12.654 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.060070 AU |
| Orbital Period | 4.578 days |
| Mean Orbital Velocity | 142.8 km/s |
| Orbital Eccentricity (e) | 0.27500 |
| Orbital Inclination (i) | 84.9800° |
| Mean Bulk Density | 0.2 g/cm³ (37.7 km/s vesc) |
| Insolation Flux | 1547.1014 S⊕ (~2,105,605 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2865.300 LY (878.521 pc) |