HAT-P-2 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-2 b is a confirmed gas giant exoplanet orbiting the star HAT-P-2, located approximately 416.7 light-years (127.77 parsecs) from the Solar System. First announced in 2007 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.4943% across the stellar disk), this world measures 10.66 Earth radii (0.95 Jupiter radii) and has a measured mass of 2866.812 Earth masses (9.02 Jupiter masses). Combining its mass and radius yields a mean bulk density of 13.05 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 25.23 g⊕ (247.42 m/s²), and an escape velocity of 183.4 km/s.
In its orbital architecture around HAT-P-2, HAT-P-2 b completes one full revolution every 5.634 Earth days at a semi-major axis of 0.06814 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 131.6 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.5172, swinging from 0.0329 AU at periapsis out to 0.1034 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1540 K (+1267°C / +2313°F) and receiving 588.52 S⊕ (~800,973 W/m²), HAT-P-2 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-2 is classified as a warm F-type star of spectral type F8 with an effective photospheric temperature of 6,380 K, a radius of 1.39 R☉, a mass of 1.33 M☉, an estimated bolometric luminosity of 2.872 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.44 Gyr and a metallicity of [Fe/H] = 0.18 dex (metal-rich relative to the Sun). From Earth, HAT-P-2 shines at apparent V-band magnitude 8.72 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HAT-P-2 system is a multi-planet architecture hosting 2 confirmed worlds, with HAT-P-2 b sharing its stellar neighborhood alongside HAT-P-2 c.
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-2 |
| Spectral Type | F8 |
| Effective Temp (Teff) | 6,380 K |
| Stellar Radius | 1.3900 R☉ |
| Stellar Mass | 1.3300 M☉ |
| Bolometric Luminosity | 2.872 L☉ |
| Metallicity [Fe/H] | 0.180 dex |
| Stellar Age | 1.440 Gyr |
| Apparent Magnitude | V: 8.720 · G: 8.598 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.068140 AU |
| Orbital Period | 5.634 days |
| Mean Orbital Velocity | 131.6 km/s |
| Orbital Eccentricity (e) | 0.51720 |
| Orbital Inclination (i) | 86.1600° |
| Mean Bulk Density | 13.05 g/cm³ (183.4 km/s vesc) |
| Insolation Flux | 588.5180 S⊕ (~800,973 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 416.700 LY (127.774 pc) |