HN Lib b
Astrophysical Synthesis & Habitability Characterization
HN Lib b is a confirmed sub-neptune exoplanet orbiting the star HN Lib, located approximately 20.4 light-years (6.24 parsecs) from the Solar System. First announced in 2023 by Calar Alto Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.2 Earth radii and has a measured mass of 5.46 Earth masses. Combining its mass and radius yields a mean bulk density of 2.83 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 17.6 km/s.
In its orbital architecture around HN Lib, HN Lib b completes one full revolution every 36.116 Earth days at a semi-major axis of 0.1417 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 42.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.079 carries the world between 0.1305 AU at periapsis and 0.1529 AU at apoapsis, driving measurable seasonal insolation cycles.
✓ Classified as a Temperate Habitable Zone Candidate.
With an estimated equilibrium temperature of 234 K (-39°C / -38°F) and an incident stellar irradiance of 0.50 S⊕ (~685 W/m²), HN Lib b orbits within the empirical circumstellar habitable zone where a rocky surface under sufficient atmospheric pressure can maintain liquid surface water.
The host star HN Lib is classified as a low-mass red dwarf of spectral type M4.0 V with an effective photospheric temperature of 3,347 K, a radius of 0.299 R☉, a mass of 0.291 M☉, an estimated bolometric luminosity of 0.01 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.4 Gyr and a metallicity of [Fe/H] = -0.18 dex (metal-poor relative to the Sun). From Earth, HN Lib shines at apparent V-band magnitude 11.311 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Calar Alto Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HN Lib |
| Spectral Type | M4.0 V |
| Effective Temp (Teff) | 3,347 K |
| Stellar Radius | 0.2990 R☉ |
| Stellar Mass | 0.2910 M☉ |
| Bolometric Luminosity | 0.01 L☉ |
| Metallicity [Fe/H] | -0.180 dex |
| Stellar Age | 4.400 Gyr |
| Apparent Magnitude | V: 11.311 · G: 9.879 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.141700 AU |
| Orbital Period | 36.116 days |
| Mean Orbital Velocity | 42.7 km/s |
| Orbital Eccentricity (e) | 0.07900 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.83 g/cm³ (17.6 km/s vesc) |
| Insolation Flux | 0.5030 S⊕ (~685 W/m²) |
| Habitable Zone Status | ★ Temperate Zone |
| Celestial Distance | 20.400 LY (6.244 pc) |