HIP 35173 b

Astrophysical Synthesis & Habitability Characterization

HIP 35173 b is a confirmed sub-neptune exoplanet orbiting the star HIP 35173, located approximately 108.1 light-years (33.16 parsecs) from the Solar System. First announced in 2019 by Las Campanas Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.61 Earth radii (0.32 Jupiter radii) and has a measured mass of 12.7 Earth masses. Combining its mass and radius yields a mean bulk density of 1.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.97 g⊕ (9.51 m/s²), and an escape velocity of 21 km/s.

In its orbital architecture around HIP 35173, HIP 35173 b completes one full revolution every 41.516 Earth days at a semi-major axis of 0.217 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 56.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.16 carries the world between 0.1823 AU at periapsis and 0.2517 AU at apoapsis, driving measurable seasonal insolation cycles.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 444 K (+171°C / +340°F) and receiving 6.50 S⊕ (~8,842 W/m²), HIP 35173 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HIP 35173 is classified as an orange K-type star of spectral type K2 V with an effective photospheric temperature of 4,881 K, a radius of 0.7734 R☉, a mass of 0.79 M☉, an estimated bolometric luminosity of 0.305 L☉. From Earth, HIP 35173 shines at apparent V-band magnitude 9.01 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere.

Discovery Facility: Las Campanas Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).