HAT-P-55 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-55 b is a confirmed gas giant exoplanet orbiting the star HAT-P-55, located approximately 1667.9 light-years (511.39 parsecs) from the Solar System. First announced in 2015 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.5162% across the stellar disk), this world measures 14.841 Earth radii (1.32 Jupiter radii) and has a measured mass of 189.426 Earth masses (0.6 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.32 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.86 g⊕ (8.43 m/s²), and an escape velocity of 40 km/s.
In its orbital architecture around HAT-P-55, HAT-P-55 b completes one full revolution every 3.585 Earth days at a semi-major axis of 0.04628 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 140.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.17 carries the world between 0.0384 AU at periapsis and 0.0541 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 583.00 S⊕ (~793,463 W/m²), HAT-P-55 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-55 is classified as a stellar host with an effective photospheric temperature of 5,804 K, a radius of 1.105 R☉, a mass of 1.028 M☉, an estimated bolometric luminosity of 1.243 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.3 Gyr and a metallicity of [Fe/H] = 0.003 dex (near-solar heavy-element abundance). From Earth, HAT-P-55 shines at apparent V-band magnitude 13.197 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HAT-P-55 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,804 K |
| Stellar Radius | 1.1050 R☉ |
| Stellar Mass | 1.0280 M☉ |
| Bolometric Luminosity | 1.243 L☉ |
| Metallicity [Fe/H] | 0.003 dex |
| Stellar Age | 5.300 Gyr |
| Apparent Magnitude | V: 13.197 · G: 13.096 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.046280 AU |
| Orbital Period | 3.585 days |
| Mean Orbital Velocity | 140.4 km/s |
| Orbital Eccentricity (e) | 0.17000 |
| Orbital Inclination (i) | 86.8000° |
| Mean Bulk Density | 0.32 g/cm³ (40 km/s vesc) |
| Insolation Flux | 583.0000 S⊕ (~793,463 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1667.900 LY (511.388 pc) |