HIP 41378 g

Astrophysical Synthesis & Habitability Characterization

HIP 41378 g is a confirmed sub-neptune exoplanet orbiting the star HIP 41378, located approximately 346.7 light-years (106.29 parsecs) from the Solar System. First announced in 2025 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.5 Earth radii and has a measured mass of 6.81 Earth masses. Combining its mass and radius yields a mean bulk density of 2.4 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.5 km/s.

In its orbital architecture around HIP 41378, HIP 41378 g completes one full revolution every 63.19 Earth days. Its moderate orbital eccentricity of e = 0.055 driving measurable seasonal insolation cycles.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 605 K (+332°C / +630°F) and receiving 22.30 S⊕ (~30,350 W/m²), HIP 41378 g orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HIP 41378 is classified as a warm F-type star of spectral type F6 with an effective photospheric temperature of 6,290 K, a radius of 1.3 R☉, a mass of 1.22 M☉, an estimated bolometric luminosity of 2.373 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.07 Gyr and a metallicity of [Fe/H] = -0.05 dex (near-solar heavy-element abundance). From Earth, HIP 41378 shines at apparent V-band magnitude 8.93 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HIP 41378 system is a multi-planet architecture hosting 6 confirmed worlds, with HIP 41378 g sharing its stellar neighborhood alongside HIP 41378 b, HIP 41378 c, HIP 41378 d, HIP 41378 e, HIP 41378 f.

Discovery Facility: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).