51 Eridani b

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51 Eri b
51 Eridani b orbit animated (2014-2018).gif
Direct imaging of 51 Eri b
Discovered byMacintosh et al.
Discovery dateDec 2014
Orbital characteristics
Eccentricity0.49 (± 0.15) [1]
Inclination136.0 (± 11.0) [1] deg
2452014.79 (± 12.0) [1] JD
84.0 (± 58.0) [1] deg
Star51 Eridani
Physical characteristics
Mean radius
Mass2.6 (± 0.3) MJ
3.5 g
Temperature700 K[2]

51 Eridani b is a "Jupiter-like" planet that orbits the young F0 V star 51 Eridani, in the constellation Eridanus.[3] It is 96 light years away from the solar system, and it is approximately 20 million years old.[4]


51 Eridani b was announced in August 2015, but was discovered in December 2014 using the Gemini Planet Imager, an international project led by the Kavli Institute for Particle Astrophysics and Cosmology. 51 Eridani b is the first exoplanet discovered by the Gemini Planet Imager.[5] The Gemini Planet Imager was specifically created to discern and evaluate dim, newer planets orbiting bright stars through “direct imaging.”[6] Direct imaging allows astronomers to use adaptive optics to sharpen the resolution of the image of a target star, then obstruct its starlight.[6] Any residual incoming light is then scrutinized, and the brightest spots suggest a possible planet.[6] Prior to the discovery of 51 Eridani b, each of the directly imaged worlds previously discovered had been gas giants many times the mass of Jupiter.[7]

Physical characteristics[edit]

The planet has a mass at least 2.6MJ, but not more than 11MJ.[8] Its radius is about 1.11 times the radius of Jupiter. It orbits 11.1 AU from its host star, and has an orbital period of roughly 10,000 days.[1] The average temperature is 807±45 K, which is substantially hotter than the 130 K average temperature of Jupiter, the planet in the Solar System of closest size.[9]


'51 Eridani b' has relatively low C/O molar ratio of 0.38±0.09.[9] The planet has the second strongest methane signature of any exoplanet, after GJ 504 b.[10] This methane signature, along with the low luminosity of the object, should produce additional clues as to how 51 Eridani b was formed.[5] Astronomers also detected the presence of water in the planet's spectrum.[11] Atmospheric modeling favors a low surface gravity and a partly cloudy atmosphere.[7]


  1. ^ a b c d e "Planet 51 Eri b". The Extrasolar Planets Encyclopaedia. Retrieved 25 December 2020.
  2. ^ Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager, B. Macintosh, and the GPIES team, Science Published Online August 13, 2015 doi:10.1126/science.aac5891.
  3. ^ Choi, Charles (August 13, 2015). "Found! 'Young Jupiter,' the Smallest Exoplanet Directly Seen by Telescope". Retrieved August 15, 2015.
  4. ^ Hadhazy, Adam (August 13, 2015). "'Young Jupiter' 51 Eridani b: Why Directly Imaging an Exoplanet Is Big". space.com. Retrieved August 15, 2015.
  5. ^ a b University, Stanford (13 August 2015). "Astronomers discover 'young Jupiter' exoplanet".
  6. ^ a b c Culler, Jessica (14 August 2015). "NASA Scientists Help Understand Newly Discovered Planet".
  7. ^ a b Billings, Lee. "Astronomers Glimpse a Young Jupiter, 51 Eridani b".
  8. ^ Limits on the Mass and Initial Entropy of 51 Eri b from Gaia EDR3 Astrometry, 2021, arXiv:2110.13173
  9. ^ a b Revisiting the atmosphere of the exoplanet 51 Eridani b with VLT/SPHERE, 2022, arXiv:2211.14330
  10. ^ "Astronomers Discover Young Planet That Looks Like Jupiter 100 Light Years Away".[dead link]
  11. ^ "Young 'alien Jupiter' discovered". 14 August 2015 – via www.bbc.co.uk.