HIP 19976 b

Astrophysical Synthesis & Habitability Characterization

HIP 19976 b is a confirmed sub-neptune exoplanet orbiting the star HIP 19976, located approximately 131.3 light-years (40.27 parsecs) from the Solar System. First announced in 2022 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.94 Earth radii (0.44 Jupiter radii) and has a measured mass of 21.612 Earth masses. Combining its mass and radius yields a mean bulk density of 0.99 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.89 g⊕ (8.73 m/s²), and an escape velocity of 23.4 km/s.

In its orbital architecture around HIP 19976, HIP 19976 b completes one full revolution every 50.659 Earth days at a semi-major axis of 0.234 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 50.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.304, swinging from 0.1629 AU at periapsis out to 0.3051 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 378 K (+105°C / +221°F) and receiving 3.41 S⊕ (~4,635 W/m²), HIP 19976 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HIP 19976 is classified as a stellar host with an effective photospheric temperature of 4,316 K, a radius of 0.7723 R☉, a mass of 0.67 M☉, an estimated bolometric luminosity of 0.186 L☉. From Earth, HIP 19976 shines at apparent V-band magnitude 10.48 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.

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