XO-5 b

Astrophysical Synthesis & Habitability Characterization

XO-5 b is a confirmed gas giant exoplanet orbiting the star XO-5, located approximately 900.9 light-years (276.21 parsecs) from the Solar System. First announced in 2008 by XO using the Transit detection technique (producing an estimated primary transit depth of 1.0751% across the stellar disk), this world measures 12.78 Earth radii (1.14 Jupiter radii) and has a measured mass of 378.2 Earth masses (1.19 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.32 g⊕ (22.75 m/s²), and an escape velocity of 60.9 km/s.

In its orbital architecture around XO-5, XO-5 b completes one full revolution every 4.188 Earth days at a semi-major axis of 0.0515 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 133.8 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 1230 K (+957°C / +1755°F) and receiving 397.48 S⊕ (~540,970 W/m²), XO-5 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star XO-5 is classified as a solar-type yellow star of spectral type G8 V with an effective photospheric temperature of 5,430 K, a radius of 1.13 R☉, a mass of 1.04 M☉, an estimated bolometric luminosity of 0.996 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.5 Gyr and a metallicity of [Fe/H] = 0.05 dex (near-solar heavy-element abundance). From Earth, XO-5 shines at apparent V-band magnitude 12.198 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

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