HAT-P-38 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-38 b is a confirmed gas giant exoplanet orbiting the star HAT-P-38, located approximately 832.4 light-years (255.21 parsecs) from the Solar System. First announced in 2012 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.8436% across the stellar disk), this world measures 9.247 Earth radii (0.82 Jupiter radii) and has a measured mass of 84.857 Earth masses (0.27 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.59 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 33.9 km/s.
In its orbital architecture around HAT-P-38, HAT-P-38 b completes one full revolution every 4.64 Earth days at a semi-major axis of 0.0523 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 122.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.067 carries the world between 0.0488 AU at periapsis and 0.0558 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1082 K (+809°C / +1488°F) and receiving 243.03 S⊕ (~330,769 W/m²), HAT-P-38 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-38 is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 5,330 K, a radius of 0.923 R☉, a mass of 0.886 M☉, an estimated bolometric luminosity of 0.617 L☉. Stellar evolution modeling indicates an estimated stellar age of 10.1 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, HAT-P-38 shines at apparent V-band magnitude 12.525 (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-38 |
| Spectral Type | G5 |
| Effective Temp (Teff) | 5,330 K |
| Stellar Radius | 0.9230 R☉ |
| Stellar Mass | 0.8860 M☉ |
| Bolometric Luminosity | 0.617 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 10.100 Gyr |
| Apparent Magnitude | V: 12.525 · G: 12.302 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.052300 AU |
| Orbital Period | 4.64 days |
| Mean Orbital Velocity | 122.6 km/s |
| Orbital Eccentricity (e) | 0.06700 |
| Orbital Inclination (i) | 88.3000° |
| Mean Bulk Density | 0.59 g/cm³ (33.9 km/s vesc) |
| Insolation Flux | 243.0337 S⊕ (~330,769 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 832.400 LY (255.206 pc) |