HAT-P-12 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-12 b is a confirmed gas giant exoplanet orbiting the star HAT-P-12, located approximately 465.6 light-years (142.75 parsecs) from the Solar System. First announced in 2009 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.9762% across the stellar disk), this world measures 10.749 Earth radii (0.96 Jupiter radii) and has a measured mass of 67.059 Earth masses (0.21 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.3 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.58 g⊕ (5.69 m/s²), and an escape velocity of 27.9 km/s.
In its orbital architecture around HAT-P-12, HAT-P-12 b completes one full revolution every 3.213 Earth days at a semi-major axis of 0.0384 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 130 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 963 K (+690°C / +1274°F) and receiving 118.08 S⊕ (~160,700 W/m²), HAT-P-12 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-12 is classified as an orange K-type star of spectral type K4 with an effective photospheric temperature of 4,650 K, a radius of 0.701 R☉, a mass of 0.733 M☉, an estimated bolometric luminosity of 0.206 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.5 Gyr and a metallicity of [Fe/H] = -0.29 dex (metal-poor relative to the Sun). From Earth, HAT-P-12 shines at apparent V-band magnitude 12.665 (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-12 |
| Spectral Type | K4 |
| Effective Temp (Teff) | 4,650 K |
| Stellar Radius | 0.7010 R☉ |
| Stellar Mass | 0.7330 M☉ |
| Bolometric Luminosity | 0.206 L☉ |
| Metallicity [Fe/H] | -0.290 dex |
| Stellar Age | 2.500 Gyr |
| Apparent Magnitude | V: 12.665 · G: 12.420 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.038400 AU |
| Orbital Period | 3.213 days |
| Mean Orbital Velocity | 130 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.0000° |
| Mean Bulk Density | 0.3 g/cm³ (27.9 km/s vesc) |
| Insolation Flux | 118.0750 S⊕ (~160,700 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 465.600 LY (142.751 pc) |