HD 86728 b
Astrophysical Synthesis & Habitability Characterization
HD 86728 b is a confirmed sub-neptune exoplanet orbiting the star HD 86728, located approximately 48.7 light-years (14.92 parsecs) from the Solar System. First announced in 2025 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.03 Earth radii (0.27 Jupiter radii) and has a measured mass of 9.43 Earth masses. Combining its mass and radius yields a mean bulk density of 1.87 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.03 g⊕ (10.1 m/s²), and an escape velocity of 19.7 km/s.
In its orbital architecture around HD 86728, HD 86728 b completes one full revolution every 31.152 Earth days at a semi-major axis of 0.1916 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 66.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.067 carries the world between 0.1788 AU at periapsis and 0.2044 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 687 K (+414°C / +777°F) and receiving 37.18 S⊕ (~50,606 W/m²), HD 86728 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 86728 is classified as a solar-type yellow star of spectral type G1V with an effective photospheric temperature of 5,610 K, a radius of 1.237 R☉, a mass of 0.967 M☉, an estimated bolometric luminosity of 1.36 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.52 Gyr and a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, HD 86728 shines at apparent V-band magnitude 5.38 (visible to the unaided human eye under dark skies) in the Northern 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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 86728 |
| Spectral Type | G1V |
| Effective Temp (Teff) | 5,610 K |
| Stellar Radius | 1.2370 R☉ |
| Stellar Mass | 0.9670 M☉ |
| Bolometric Luminosity | 1.36 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | 9.520 Gyr |
| Apparent Magnitude | V: 5.380 · G: 5.209 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.191600 AU |
| Orbital Period | 31.152 days |
| Mean Orbital Velocity | 66.9 km/s |
| Orbital Eccentricity (e) | 0.06700 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.87 g/cm³ (19.7 km/s vesc) |
| Insolation Flux | 37.1828 S⊕ (~50,606 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 48.700 LY (14.920 pc) |