HATS-42 b

Astrophysical Synthesis & Habitability Characterization

HATS-42 b is a confirmed gas giant exoplanet orbiting the star HATS-42, located approximately 2610.5 light-years (800.38 parsecs) from the Solar System. First announced in 2018 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 0.945% across the stellar disk), this world measures 15.693 Earth radii (1.4 Jupiter radii) and has a measured mass of 597.52 Earth masses (1.88 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.85 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.43 g⊕ (23.83 m/s²), and an escape velocity of 69 km/s.

In its orbital architecture around HATS-42, HATS-42 b completes one full revolution every 2.292 Earth days at a semi-major axis of 0.03689 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 175.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.229 carries the world between 0.0284 AU at periapsis and 0.0453 AU at apoapsis, driving measurable seasonal insolation cycles.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1856 K (+1583°C / +2881°F) and receiving 1,637.21 S⊕ (~2,228,237 W/m²), HATS-42 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HATS-42 is classified as a stellar host with an effective photospheric temperature of 6,060 K, a radius of 1.48 R☉, a mass of 1.273 M☉, an estimated bolometric luminosity of 2.65 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.26 Gyr and a metallicity of [Fe/H] = 0.22 dex (metal-rich relative to the Sun). From Earth, HATS-42 shines at apparent V-band magnitude 13.682 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.

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