HIP 86221 b

Astrophysical Synthesis & Habitability Characterization

HIP 86221 b is a confirmed gas giant exoplanet orbiting the star HIP 86221, located approximately 96.2 light-years (29.49 parsecs) from the Solar System. First announced in 2021 by Cerro Tololo Inter-American Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14 Earth radii (1.25 Jupiter radii) and has a measured mass of 225.658 Earth masses (0.71 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.45 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.15 g⊕ (11.28 m/s²), and an escape velocity of 44.9 km/s.

In its orbital architecture around HIP 86221, HIP 86221 b completes one full revolution every 2.224 Earth days at a semi-major axis of 0.031 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 151.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.086 carries the world between 0.0283 AU at periapsis and 0.0337 AU at apoapsis, driving measurable seasonal insolation cycles.

☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 14.000 R⊕, HIP 86221 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.

The host star HIP 86221 is classified as an orange K-type star of spectral type K5 V with a mass of 0.79 M☉. From Earth, HIP 86221 shines at apparent V-band magnitude 9.25 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere.

Discovery Facility: Cerro Tololo Inter-American Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).