Astronomy:51 Eridani b

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51 Eri b
Direct imaging of 51 Eri b
Discovery
Discovered byMacintosh et al.
Discovery dateDec 2014
Imaged
Orbital characteristics[1]
9.1+0.6
−0.2 astronomical unit|AU
Eccentricity0.55+0.03
−0.07
Orbital period23.5+1.7
−0.9 years
Inclination159°+6°
−11°
Longitude of ascending node58°+81°
−48°
55°+51°
−31°
Star51 Eridani
Physical characteristics[3]
Mean radius1.11+0.16
−0.13 RJ
Mass<9.5 MJ (2σ)[2]
4.26+0.24
−0.25 cgs
Physics760 ± 22 K (486.9 ± 22.0 °C)
Atmosphere[4][5][6]
Composition by volumemethane, water vapour, ammonia, carbon dioxide


51 Eridani b is a "Jupiter-like" planet that orbits the young F0 V star 51 Eridani, in the constellation Eridanus.[7] It is 96 light-years (29 parsecs) away from the Solar system, and it is approximately 20 million years old.[8]

Discovery

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.[9] 51 Eridani b is the first exoplanet discovered by the Gemini Planet Imager.[4] The Gemini Planet Imager was specifically created to discern and evaluate dim, newer planets orbiting bright stars through “direct imaging.”[10] Direct imaging allows astronomers to use adaptive optics to sharpen the resolution of the image of a target star, then obstruct its starlight.[10] Any residual incoming light is then scrutinized, and the brightest spots suggest a possible planet.[10] 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.[11]

Physical characteristics

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.[2] Astrometric data from the Gaia spacecraft has set an upper limit of 9.5 MJ at 2-sigma confidence.[2] 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..[6][12] 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.[1]

Atmosphere

51 Eridani b has relatively low C/O molar ratio of 0.38±0.09.[13] The planet has the second strongest methane (CH4) signature of any exoplanet, after Gliese 504 b.[14] This methane signature, along with the low luminosity of the object, should give additional clues as to how 51 Eridani b was formed.[4] Astronomers also detected the presence of water vapour[15] and ammonia (NH3)[5] in the planet's spectrum. Atmospheric modeling favors a low surface gravity and a partly cloudy atmosphere.[11]

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.[6]

References

  1. ↑ 1.0 1.1 Denis, A.; Vigan, A.; Chauvin, G.; Lacquement, A.; Beust, H.; Ravet, M.; Costes, J.; Radcliffe, A. et al. (2026-03-01). "Eccentric and cool: A high-spectral-resolution view of 51 Eri b with VLT/HiRISE" (in en). Astronomy & Astrophysics 707: L13. doi:10.1051/0004-6361/202658862. ISSN 0004-6361. 
  2. ↑ 2.0 2.1 2.2 Elliott, Ashley; Boyajian, Tabetha; Ellis, Tyler; von Braun, Kaspar; Mann, Andrew W.; Schaefer, Gail (2024). "Measuring the stellar and planetary parameters of the 51 Eridani system". Publications of the Astronomical Society of Australia 41. doi:10.1017/pasa.2024.40. Bibcode: 2024PASA...41...43E. 
  3. ↑ Samland, M.; Mollière, P.; Bonnefoy, M.; Maire, A.-L.; Cantalloube, F.; Cheetham, A. C.; Mesa, D.; Gratton, R. et al. (July 2017). "Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE". Astronomy & Astrophysics 603: A57. doi:10.1051/0004-6361/201629767. ISSN 0004-6361. Bibcode: 2017A&A...603A..57S. http://www.aanda.org/10.1051/0004-6361/201629767. 
  4. ↑ 4.0 4.1 4.2 University, Stanford (13 August 2015). "Astronomers discover 'young Jupiter' exoplanet". http://news.stanford.edu/news/2015/august/exoplanet-macintosh-eridani-081315.html. 
  5. ↑ 5.0 5.1 Whiteford, Niall; Glasse, Alistair; Chubb, Katy L.; Kitzmann, Daniel; Ray, Shrishmoy; Phillips, Mark W.; Biller, Beth A.; Palmer, Paul I. et al. (2023), "Retrieval study of cool directly imaged exoplanet 51 Eri B", Monthly Notices of the Royal Astronomical Society 525: 1375–1400, doi:10.1093/mnras/stad670 
  6. ↑ 6.0 6.1 6.2 Balmer, William O.; Kammerer, Jens; Pueyo, Laurent; Perrin, Marshall D.; Girard, Julien H.; Leisenring, Jarron M.; Lawson, Kellen; Dennen, Henry et al. (2025-03-17). "JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO2 in the HR 8799 and 51 Eri Exoplanets' Atmospheres". The Astronomical Journal 169 (4): 209. doi:10.3847/1538-3881/adb1c6. ISSN 0004-6256. 
  7. ↑ Choi, Charles (August 13, 2015). "Found! 'Young Jupiter,' the Smallest Exoplanet Directly Seen by Telescope". http://www.space.com/30248-young-jupiter-smallest-directly-imaged-exoplanet.html. 
  8. ↑ Hadhazy, Adam (August 13, 2015). "'Young Jupiter' 51 Eridani b: Why Directly Imaging an Exoplanet Is Big". space.com. http://www.space.com/30238-young-jupiter-exoplanet-51-eridani-b-explained.html. 
  9. ↑ 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.
  10. ↑ 10.0 10.1 10.2 Culler, Jessica (14 August 2015). "NASA Scientists Help Understand Newly Discovered Planet". http://www.nasa.gov/feature/ames/nasa-scientists-help-understand-newly-discovered-planet. 
  11. ↑ 11.0 11.1 Billings, Lee. "Astronomers Glimpse a Young Jupiter, 51 Eridani b". http://www.scientificamerican.com/article/astronomers-glimpse-a-young-jupiter-51-eridani-b/. 
  12. ↑ "Exoplanet 51 Eridani b: A Red-Hot Young Jupiter Around Distant Star - Infographic". http://www.space.com/30239-young-jupiter-exoplanet-51-eridani-b.html. 
  13. ↑ Brown-Sevilla, S. B.; Maire, A. -L.; Mollière, P.; Samland, M.; Feldt, M.; Brandner, W.; Henning, Th.; Gratton, R. et al. (2023), "Revisiting the atmosphere of the exoplanet 51 Eridani b with VLT/SPHERE", Astronomy & Astrophysics 673: A98, doi:10.1051/0004-6361/202244826, Bibcode: 2023A&A...673A..98B 
  14. ↑ "Astronomers Discover Young Planet That Looks Like Jupiter 100 Light Years Away". 13 August 2015. https://www.independent.co.uk/news/science/51-eridani-b-astronomers-discover-young-planet-that-looks-like-jupiter-100-light-years-away-10454531.html%7Cdate. 
  15. ↑ "Young 'alien Jupiter' discovered". BBC News. 14 August 2015. https://www.bbc.co.uk/news/science-environment-33922503. 



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