HATS-55 b
Astrophysical Synthesis & Habitability Characterization
HATS-55 b is a confirmed gas giant exoplanet orbiting the star HATS-55, located approximately 1989 light-years (609.84 parsecs) from the Solar System. First announced in 2019 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 1.3034% across the stellar disk), this world measures 14.022 Earth radii (1.25 Jupiter radii) and has a measured mass of 292.721 Earth masses (0.92 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.59 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.49 g⊕ (14.61 m/s²), and an escape velocity of 51.1 km/s.
In its orbital architecture around HATS-55, HATS-55 b completes one full revolution every 4.204 Earth days at a semi-major axis of 0.05412 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 140 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.092 carries the world between 0.0491 AU at periapsis and 0.0591 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1367 K (+1094°C / +2001°F) and receiving 355.91 S⊕ (~484,392 W/m²), HATS-55 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-55 is classified as a stellar host with an effective photospheric temperature of 6,214 K, a radius of 1.126 R☉, a mass of 1.1955 M☉, an estimated bolometric luminosity of 1.696 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.4 Gyr and a metallicity of [Fe/H] = 0.108 dex (metal-rich relative to the Sun). From Earth, HATS-55 shines at apparent V-band magnitude 13.525 (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-55 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,214 K |
| Stellar Radius | 1.1260 R☉ |
| Stellar Mass | 1.1955 M☉ |
| Bolometric Luminosity | 1.696 L☉ |
| Metallicity [Fe/H] | 0.108 dex |
| Stellar Age | 0.400 Gyr |
| Apparent Magnitude | V: 13.525 · G: 13.350 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.054120 AU |
| Orbital Period | 4.204 days |
| Mean Orbital Velocity | 140 km/s |
| Orbital Eccentricity (e) | 0.09200 |
| Orbital Inclination (i) | 86.3200° |
| Mean Bulk Density | 0.59 g/cm³ (51.1 km/s vesc) |
| Insolation Flux | 355.9090 S⊕ (~484,392 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1989.000 LY (609.838 pc) |