HAT-P-27 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-27 b is a confirmed gas giant exoplanet orbiting the star HAT-P-27, located approximately 649.6 light-years (199.17 parsecs) from the Solar System. First announced in 2011 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.4686% across the stellar disk), this world measures 11.43 Earth radii (1.02 Jupiter radii) and has a measured mass of 197.05 Earth masses (0.62 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.73 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.51 g⊕ (14.81 m/s²), and an escape velocity of 46.4 km/s.
In its orbital architecture around HAT-P-27, HAT-P-27 b completes one full revolution every 3.04 Earth days at a semi-major axis of 0.04 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 143.2 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1092 K (+819°C / +1506°F) and receiving 336.04 S⊕ (~457,348 W/m²), HAT-P-27 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-27 is classified as a solar-type yellow star of spectral type G8 with an effective photospheric temperature of 5,316 K, a radius of 0.8647 R☉, a mass of 0.916 M☉, an estimated bolometric luminosity of 0.536 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.4 Gyr and a metallicity of [Fe/H] = 0.3 dex (metal-rich relative to the Sun). From Earth, HAT-P-27 shines at apparent V-band magnitude 12.052 (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-27 |
| Spectral Type | G8 |
| Effective Temp (Teff) | 5,316 K |
| Stellar Radius | 0.8647 R☉ |
| Stellar Mass | 0.9160 M☉ |
| Bolometric Luminosity | 0.536 L☉ |
| Metallicity [Fe/H] | 0.300 dex |
| Stellar Age | 4.400 Gyr |
| Apparent Magnitude | V: 12.052 · G: 11.956 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.040000 AU |
| Orbital Period | 3.04 days |
| Mean Orbital Velocity | 143.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 85.0000° |
| Mean Bulk Density | 0.73 g/cm³ (46.4 km/s vesc) |
| Insolation Flux | 336.0384 S⊕ (~457,348 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 649.600 LY (199.173 pc) |