4 UMa b
4 UMa b is a cold gas giant orbiting the K1 III star 4 UMa in the constellation Ursa Major. It lies about 240 light-years from Earth and was discovered in 2006 using the radial velocity method.
Is 4 UMa b in the Habitable Zone?
4 UMa b orbits inside the inner edge of the habitable zone of 4 UMa. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of 4 UMa: 8.480–21.034 AU (conservative: 10.741–19.942 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on 4 UMa b — one full orbit around 4 UMa — lasts 270.3 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.877 AU — comparable to the inner Solar System. Its orbit is highly elliptical (eccentricity 0.45), swinging dramatically closer to and farther from its star.
How Was 4 UMa b Discovered?
4 UMa b was discovered in 2006 using the radial velocity method, with observations from Thueringer Landessternwarte Tautenburg.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is 4 UMa b?
4 UMa b is 239.6 light-years (73.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1787. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,216,960 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. 4 UMa b scores 0.08, ranking #4,742 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: 4 UMa
4 UMa
- Spectral type
- K1 III
- Surface temperature
- 4,415 K (Sun: 5,772 K)
- Mass
- 1.23 M☉
- Radius
- 18.11 R☉
- Age
- 4.6 billion years (Sun: 4.6)
Planetary System
4 UMa b is the only planet known to orbit 4 UMa so far.
4 UMa b — Complete Data
| Mass (best estimate) | 2,511.48 Earth masses |
|---|---|
| Orbital period | 270.27 days |
| Orbital distance | 0.877 AU |
| Eccentricity | 0.453 |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 239.6 light-years (73.5 parsecs) |
| Constellation | Ursa Major |
| Discovery method | Radial Velocity |
| Discovery facility | Thueringer Landessternwarte Tautenburg |
| Discovery year | 2006 |
Data: NASA Exoplanet Archive, last updated 2023-09-19. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About 4 UMa b
Is 4 UMa b habitable?
No — 4 UMa b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is 4 UMa b?
4 UMa b is about 240 light-years from Earth in the constellation Ursa Major. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,216,960 years to get there.
How long is a year on 4 UMa b?
One orbit around 4 UMa takes 270.3 Earth days.
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