4 UMa b
Astrophysical Synthesis & Habitability Characterization
4 UMa b is a confirmed gas giant exoplanet orbiting the star 4 UMa, located approximately 239.6 light-years (73.46 parsecs) from the Solar System. First announced in 2006 by Thueringer Landessternwarte Tautenburg using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.6 Earth radii (1.12 Jupiter radii) and has a measured mass of 2511.48 Earth masses (7.9 Jupiter masses). Combining its mass and radius yields a mean bulk density of 6.92 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 15.82 g⊕ (155.14 m/s²), and an escape velocity of 157.9 km/s.
In its orbital architecture around 4 UMa, 4 UMa b completes one full revolution every 270.27 Earth days at a semi-major axis of 0.877 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 35.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.453, swinging from 0.4797 AU at periapsis out to 1.2743 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 967 K (+694°C / +1281°F) and receiving 150.09 S⊕ (~204,276 W/m²), 4 UMa b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star 4 UMa is classified as an orange K-type star of spectral type K1 III with an effective photospheric temperature of 4,415 K, a radius of 18.11 R☉, a mass of 1.234 M☉, an estimated bolometric luminosity of 111.802 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.604 Gyr and a metallicity of [Fe/H] = -0.25 dex (metal-poor relative to the Sun). From Earth, 4 UMa shines at apparent V-band magnitude 4.58 (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: Thueringer Landessternwarte Tautenburg · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | 4 UMa |
| Spectral Type | K1 III |
| Effective Temp (Teff) | 4,415 K |
| Stellar Radius | 18.1100 R☉ |
| Stellar Mass | 1.2340 M☉ |
| Bolometric Luminosity | 111.802 L☉ |
| Metallicity [Fe/H] | -0.250 dex |
| Stellar Age | 4.604 Gyr |
| Apparent Magnitude | V: 4.580 · G: 4.238 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.877000 AU |
| Orbital Period | 270.27 days |
| Mean Orbital Velocity | 35.3 km/s |
| Orbital Eccentricity (e) | 0.45300 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 6.92 g/cm³ (157.9 km/s vesc) |
| Insolation Flux | 150.0929 S⊕ (~204,276 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 239.600 LY (73.460 pc) |