8 UMi b
Astrophysical Synthesis & Habitability Characterization
8 UMi b is a confirmed gas giant exoplanet orbiting the star 8 UMi, located approximately 530.2 light-years (162.55 parsecs) from the Solar System. First announced in 2015 by Bohyunsan Optical Astronomical Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.5 Earth radii (1.2 Jupiter radii) and has a measured mass of 524.417 Earth masses (1.65 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.18 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.88 g⊕ (28.24 m/s²), and an escape velocity of 69.7 km/s.
In its orbital architecture around 8 UMi, 8 UMi b completes one full revolution every 93.31 Earth days at a semi-major axis of 0.462 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 53.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.062 carries the world between 0.4334 AU at periapsis and 0.4906 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1126 K (+853°C / +1567°F) and receiving 247.84 S⊕ (~337,311 W/m²), 8 UMi b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star 8 UMi is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 4,847 K, a radius of 10.73 R☉, a mass of 1.51 M☉, an estimated bolometric luminosity of 57.014 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.7 Gyr and a metallicity of [Fe/H] = -0.03 dex (near-solar heavy-element abundance). From Earth, 8 UMi shines at apparent V-band magnitude 6.833 (accessible to binoculars and small amateur telescopes) 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: Bohyunsan Optical Astronomical Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | 8 UMi |
| Spectral Type | K0 |
| Effective Temp (Teff) | 4,847 K |
| Stellar Radius | 10.7300 R☉ |
| Stellar Mass | 1.5100 M☉ |
| Bolometric Luminosity | 57.014 L☉ |
| Metallicity [Fe/H] | -0.030 dex |
| Stellar Age | 1.700 Gyr |
| Apparent Magnitude | V: 6.833 · G: 6.559 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.462000 AU |
| Orbital Period | 93.31 days |
| Mean Orbital Velocity | 53.9 km/s |
| Orbital Eccentricity (e) | 0.06200 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.18 g/cm³ (69.7 km/s vesc) |
| Insolation Flux | 247.8402 S⊕ (~337,311 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 530.200 LY (162.552 pc) |