HAT-P-42 b

Astrophysical Synthesis & Habitability Characterization

HAT-P-42 b is a confirmed gas giant exoplanet orbiting the star HAT-P-42, located approximately 1321.7 light-years (405.24 parsecs) from the Solar System. First announced in 2012 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.7392% across the stellar disk), this world measures 14.348 Earth radii (1.28 Jupiter radii) and has a measured mass of 331.801 Earth masses (1.04 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.62 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.61 g⊕ (15.79 m/s²), and an escape velocity of 53.8 km/s.

In its orbital architecture around HAT-P-42, HAT-P-42 b completes one full revolution every 4.642 Earth days at a semi-major axis of 0.0575 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 134.8 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 1428 K (+1155°C / +2111°F) and receiving 684.10 S⊕ (~931,056 W/m²), HAT-P-42 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HAT-P-42 is classified as a stellar host with an effective photospheric temperature of 5,743 K, a radius of 1.53 R☉, a mass of 1.178 M☉, an estimated bolometric luminosity of 2.285 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.2 Gyr and a metallicity of [Fe/H] = 0.27 dex (metal-rich relative to the Sun). From Earth, HAT-P-42 shines at apparent V-band magnitude 12.125 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

Discovery Facility: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).