HIP 4845 b

Astrophysical Synthesis & Habitability Characterization

HIP 4845 b is a confirmed sub-neptune exoplanet orbiting the star HIP 4845, located approximately 68.8 light-years (21.1 parsecs) from the Solar System. First announced in 2020 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.89 Earth radii (0.35 Jupiter radii) and has a measured mass of 14.4 Earth masses. Combining its mass and radius yields a mean bulk density of 1.35 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.95 g⊕ (9.32 m/s²), and an escape velocity of 21.5 km/s.

In its orbital architecture around HIP 4845, HIP 4845 b completes one full revolution every 34.15 Earth days at a semi-major axis of 0.176 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 56.1 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 0.132 AU at periapsis out to 0.22 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 358 K (+85°C / +185°F) and receiving 2.99 S⊕ (~4,064 W/m²), HIP 4845 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HIP 4845 is classified as an orange K-type star of spectral type K7V with an effective photospheric temperature of 4,010 K, a radius of 0.604 R☉, a mass of 0.62 M☉, an estimated bolometric luminosity of 0.085 L☉. From Earth, HIP 4845 shines at apparent V-band magnitude 10.06 (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).