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51 Eridani b
51 Eridani b is a "Jupiter-like" planet that orbits the young F0 V star 51 Eridani, in the constellation Eridanus. It is 96 light-years (29 parsecs) away from the Solar system, and it is approximately 20 million years old.
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. The Gemini Planet Imager was specifically created to discern and evaluate dim, newer planets orbiting bright stars through “direct imaging.” Direct imaging allows astronomers to use adaptive optics to sharpen the resolution of the image of a target star, then obstruct its starlight. Any residual incoming light is then scrutinized, and the brightest spots suggest a possible planet. 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.
51 Eridani b has a mass of 4.1±0.4 Jupiter masses (MJ), based on the predictions of substellar evolution models for its effective temperature and age. Astrometric data from the Gaia spacecraft has set an upper limit of 9.5 MJ at 2-sigma confidence. Its radius is about 1.30 times the radius of Jupiter (RJ), and its effective temperature is 632 ± 13 K (358.9 ± 13.0 °C), which is substantially hotter than the 128 K average temperature of Jupiter, the planet in the Solar System of closest size.. It orbits at 9.1 AU from its host star, has an orbital period of roughly 23.5 years, following an eccentric path with e = 0.55. The higher than expected eccentricity indicates that there is another body gravitationally perturbing the planet's orbit.
51 Eridani b has relatively low C/O molar ratio of 0.38±0.09. The planet has the second strongest methane (CH4) signature of any exoplanet, after Gliese 504 b. This methane signature, along with the low luminosity of the object, should give additional clues as to how 51 Eridani b was formed. Astronomers also detected the presence of water vapour and ammonia (NH3) in the planet's spectrum. Atmospheric modeling favors a low surface gravity and a partly cloudy atmosphere.
The detection of water and carbon dioxide (CO2) in the planetary atmosphere was announced in 2025. It was the second time CO2 was directly (as opposed to by transit spectra) detected in an exoplanet.
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51 Eridani b
51 Eridani b is a "Jupiter-like" planet that orbits the young F0 V star 51 Eridani, in the constellation Eridanus. It is 96 light-years (29 parsecs) away from the Solar system, and it is approximately 20 million years old.
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. The Gemini Planet Imager was specifically created to discern and evaluate dim, newer planets orbiting bright stars through “direct imaging.” Direct imaging allows astronomers to use adaptive optics to sharpen the resolution of the image of a target star, then obstruct its starlight. Any residual incoming light is then scrutinized, and the brightest spots suggest a possible planet. 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.
51 Eridani b has a mass of 4.1±0.4 Jupiter masses (MJ), based on the predictions of substellar evolution models for its effective temperature and age. Astrometric data from the Gaia spacecraft has set an upper limit of 9.5 MJ at 2-sigma confidence. Its radius is about 1.30 times the radius of Jupiter (RJ), and its effective temperature is 632 ± 13 K (358.9 ± 13.0 °C), which is substantially hotter than the 128 K average temperature of Jupiter, the planet in the Solar System of closest size.. It orbits at 9.1 AU from its host star, has an orbital period of roughly 23.5 years, following an eccentric path with e = 0.55. The higher than expected eccentricity indicates that there is another body gravitationally perturbing the planet's orbit.
51 Eridani b has relatively low C/O molar ratio of 0.38±0.09. The planet has the second strongest methane (CH4) signature of any exoplanet, after Gliese 504 b. This methane signature, along with the low luminosity of the object, should give additional clues as to how 51 Eridani b was formed. Astronomers also detected the presence of water vapour and ammonia (NH3) in the planet's spectrum. Atmospheric modeling favors a low surface gravity and a partly cloudy atmosphere.
The detection of water and carbon dioxide (CO2) in the planetary atmosphere was announced in 2025. It was the second time CO2 was directly (as opposed to by transit spectra) detected in an exoplanet.