HAT-P-20 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-20 b is a confirmed gas giant exoplanet orbiting the star HAT-P-20, located approximately 231.7 light-years (71.04 parsecs) from the Solar System. First announced in 2010 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.6481% across the stellar disk), this world measures 9.718 Earth radii (0.87 Jupiter radii) and has a measured mass of 2302.899 Earth masses (7.25 Jupiter masses). Combining its mass and radius yields a mean bulk density of 13.84 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 24.38 g⊕ (239.09 m/s²), and an escape velocity of 172.2 km/s.
In its orbital architecture around HAT-P-20, HAT-P-20 b completes one full revolution every 2.875 Earth days at a semi-major axis of 0.0361 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 136.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.015 (ranging from 0.0356 AU at periapsis to 0.0366 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 970 K (+697°C / +1287°F) and receiving 85.12 S⊕ (~115,844 W/m²), HAT-P-20 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-20 is classified as an orange K-type star of spectral type K3 with an effective photospheric temperature of 4,595 K, a radius of 0.694 R☉, a mass of 0.756 M☉, an estimated bolometric luminosity of 0.193 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.7 Gyr and a metallicity of [Fe/H] = 0.35 dex (metal-rich relative to the Sun). From Earth, HAT-P-20 shines at apparent V-band magnitude 11.231 (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-20 |
| Spectral Type | K3 |
| Effective Temp (Teff) | 4,595 K |
| Stellar Radius | 0.6940 R☉ |
| Stellar Mass | 0.7560 M☉ |
| Bolometric Luminosity | 0.193 L☉ |
| Metallicity [Fe/H] | 0.350 dex |
| Stellar Age | 6.700 Gyr |
| Apparent Magnitude | V: 11.231 · G: 10.990 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.036100 AU |
| Orbital Period | 2.875 days |
| Mean Orbital Velocity | 136.6 km/s |
| Orbital Eccentricity (e) | 0.01500 |
| Orbital Inclination (i) | 86.8000° |
| Mean Bulk Density | 13.84 g/cm³ (172.2 km/s vesc) |
| Insolation Flux | 85.1168 S⊕ (~115,844 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 231.700 LY (71.037 pc) |