51 Eri b
51 Eri b is a cold gas giant orbiting 51 Eri in the constellation Eridanus. It lies about 97 light-years from Earth and was discovered in 2015 using the imaging method.
Is 51 Eri b in the Habitable Zone?
The position of 51 Eri b relative to the habitable zone of 51 Eri cannot be precisely determined from the available orbital data.
Orbit and Year Length
A year on 51 Eri b — one full orbit around 51 Eri — lasts 9,100.0 Earth days, longer than Jupiter's 12-year orbit. It orbits at an average distance of 10.400 AU. Its orbit is highly elliptical (eccentricity 0.57), swinging dramatically closer to and farther from its star.
How Was 51 Eri b Discovered?
51 Eri b was discovered in 2015 using the imaging method, with observations from Gemini Observatory.
Direct imaging captures actual pictures of a planet by blocking out the overwhelming glare of its host star. It works best for young, hot, massive planets on wide orbits.
How Far Away Is 51 Eri b?
51 Eri b is 97.1 light-years (29.8 parsecs) from Earth. Light arriving here tonight left the planet around the year 1929. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,708,960 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. 51 Eri b scores 0.11, ranking #4,364 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: 51 Eri
51 Eri b belongs to a system of 3 stars; it orbits 51 Eri.
51 Eri
- Mass
- 1.75 M☉
Planetary System
51 Eri b is the only planet known to orbit 51 Eri so far.
51 Eri b — Complete Data
| Mass | 3,464.33 Earth masses (10.900 Jupiter masses) |
|---|---|
| Orbital period | 9,100.00 days |
| Orbital distance | 10.400 AU |
| Eccentricity | 0.570 |
| Earth Similarity Index | 0.11 |
| Distance from Earth | 97.1 light-years (29.8 parsecs) |
| Constellation | Eridanus |
| Discovery method | Imaging |
| Discovery facility | Gemini Observatory |
| Discovery year | 2015 |
Data: NASA Exoplanet Archive, last updated 2025-09-25. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About 51 Eri b
Is 51 Eri b habitable?
51 Eri b is not known to orbit within the habitable zone of 51 Eri, and as a cold gas giant it is an unlikely candidate for life as we know it.
How far away is 51 Eri b?
51 Eri b is about 97 light-years from Earth in the constellation Eridanus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,708,960 years to get there.
How long is a year on 51 Eri b?
One orbit around 51 Eri takes 9,100.0 Earth days.
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