HATS-51 b
Astrophysical Synthesis & Habitability Characterization
HATS-51 b is a confirmed gas giant exoplanet orbiting the star HATS-51, located approximately 1270.6 light-years (389.57 parsecs) from the Solar System. First announced in 2017 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 1.0125% across the stellar disk), this world measures 15.805 Earth radii (1.41 Jupiter radii) and has a measured mass of 244.093 Earth masses (0.77 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 44 km/s.
In its orbital architecture around HATS-51, HATS-51 b completes one full revolution every 3.349 Earth days at a semi-major axis of 0.04639 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 150.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.33, swinging from 0.0311 AU at periapsis out to 0.0617 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1553 K (+1280°C / +2336°F) and receiving 740.22 S⊕ (~1,007,446 W/m²), HATS-51 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-51 is classified as a stellar host with an effective photospheric temperature of 5,758 K, a radius of 1.44 R☉, a mass of 1.187 M☉, an estimated bolometric luminosity of 2.045 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.74 Gyr. From Earth, HATS-51 shines at apparent V-band magnitude 12.525 (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-51 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,758 K |
| Stellar Radius | 1.4400 R☉ |
| Stellar Mass | 1.1870 M☉ |
| Bolometric Luminosity | 2.045 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | 4.740 Gyr |
| Apparent Magnitude | V: 12.525 · G: 12.329 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.046390 AU |
| Orbital Period | 3.349 days |
| Mean Orbital Velocity | 150.7 km/s |
| Orbital Eccentricity (e) | 0.33000 |
| Orbital Inclination (i) | 87.1000° |
| Mean Bulk Density | 0.34 g/cm³ (44 km/s vesc) |
| Insolation Flux | 740.2246 S⊕ (~1,007,446 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1270.600 LY (389.570 pc) |