COCONUTS-2b

COCONUTS-2 b, or WISEPA J075108.79-763449.6, is a gas giant exoplanet that orbits the M-type star L 34-26. With a mass of 6.3 Jupiters, it takes over one million years to complete one orbit around the star, and it is 7,506 AU away from it.[1]

COCONUTS-2b
COCONUTS-2b with unWISE. The planet in the center of the image stands out due to its red color. The host star is not pictured here.
Discovery
Discovered byZhoujian Zhang
Michael Liu
Zach Claytor
William Best
Trent Dupuy
Robert Siverd[1]
Discovery date2011
July 2021[2]
Direct imaging
Designations
WISEPA J075108.79-763449.6
Orbital characteristics
7,506.0 AU (1.12288×1012 km)[3] or ~0.1185 ly (~0.03633 pc)
1101369.9 years[3]
StarL 34-26
Physical characteristics
Mean radius
1.12±0.04 RJ[4]
Mass6.3+1.5
−1.9 MJ[5][3]
4.11+0.11
−0.18 dex[5]
Temperature434 ± 9 K[5]
Spectral type
T9

    The planet was discovered in 2011 and was initially identified as a T9 free-floating brown dwarf WISEPA J075108.79−763449.6.[6] During the COol Companions ON Ultrawide orbiTS (COCONUTS) survey, its association with L 34-26 was announced in 2021.[7] At a distance of 10.9 pc, COCONUTS-2b is the closest directly imaged exoplanet to Earth known to date.[8]

    The researchers found that it is unlikely that COCONUTS-2b was formed inside the protoplanetary disk of the host star and it is more likely that the planet formed on its own via high entropy formation (aka hot-start process).[5][9]

    Atmosphere

    The planet has a spectral type of T9, based on a low signal-to-noise near-infrared spectrum with Magellan/FIRE.[6][5] This spectral type suggests high amounts of methane, water vapor and low amounts of carbon monoxide in the atmosphere of COCONUTS-2b.

    COCONUTS-2b might have both clouds and a non-equilibrium process in its atmosphere.[5]

    Due to its large orbital separation, COCONUTS-2b is a great laboratory to study the atmosphere and composition of young gas-giant exoplanets.[2] Astronomers estimate the planet’s temperature to be around 434 K (161 °C; 322 °F).[5]

    Host star

    L 34-26, also known as COCONUTS-2A and TYC 9381-1809-1, is a M3-type dwarf star located 35 light-years away, in the constellation of Chamaeleon. The star is about one-third the mass of the Sun, with an age between 150 and 800 million years old.[10]

    Researchers using TESS found that L 34-26 showed stellar flares about every 0.48 days. It was the most active planet hosting star in their sample. The team studying the host star also found that L 34-26 is fast rotating with a rotation period of 2.83 days. The planet should not be influenced by the flares, because of the large orbital separation.[11]

    • The COCONUTS-2 system with unWISE
      The COCONUTS-2 system with unWISE
    • The planet COCONUTS-2b with Gemini-South
      The planet COCONUTS-2b with Gemini-South
    • Allwise image by the discoverers, showing planet COCONUTS-2b
      Allwise image by the discoverers, showing planet COCONUTS-2b

    References
    1. "Massive COCONUTS exoplanet discovery led by UH grad student | University of Hawaiʻi System News". University of Hawaiʻi News. University of Hawaiʻi at Mānoa. Archived from the original on 15 December 2021. Retrieved 21 December 2021.
    2. Kooser, Amanda. "Massive exoplanet 'Coconuts-2b' could help reveal the secrets of young gas giants". CNET. Archived from the original on 21 December 2021. Retrieved 21 December 2021.
    3. "COCONUTS-2 b". Exoplanet Exploration: Planets Beyond our Solar System. National Aeronautics and Space Administration. Archived from the original on 22 November 2021. Retrieved 21 December 2021.
    4. "COCONUTS-2". Open Exoplanet Catalogue. Archived from the original on 21 December 2021. Retrieved 21 December 2021.
    5. Zhang, Zhoujian; Liu, Michael C.; Claytor, Zachary R.; Best, William M. J.; Dupuy, Trent J.; Siverd, Robert J. (2021-08-01). "The Second Discovery from the COCONUTS Program: A Cold Wide-orbit Exoplanet around a Young Field M Dwarf at 10.9 pc". The Astrophysical Journal. 916 (2): L11. arXiv:2107.02805. Bibcode:2021ApJ...916L..11Z. doi:10.3847/2041-8213/ac1123. ISSN 0004-637X.
    6. Kirkpatrick, J. Davy; Cushing, Michael C.; Gelino, Christopher R.; Griffith, Roger L.; Skrutskie, Michael F.; Marsh, Kenneth A.; Wright, Edward L.; Mainzer, A.; Eisenhardt, Peter R.; McLean, Ian S.; Thompson, Maggie A.; Bauer, James M.; Benford, Dominic J.; Bridge, Carrie R.; Lake, Sean E. (2011-12-01). "The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)". The Astrophysical Journal Supplement Series. 197 (2): 19. arXiv:1108.4677. Bibcode:2011ApJS..197...19K. doi:10.1088/0067-0049/197/2/19. ISSN 0067-0049. S2CID 16850733.
    7. "Exoplanet-catalog". Exoplanet Exploration: Planets Beyond our Solar System. Archived from the original on 2021-11-22. Retrieved 2021-11-22.
    8. Siegel, Ethan. "Astronomers Go Nuts For Closest Exoplanet Directly Imaged Ever: COCONUTS-2b". Forbes. Archived from the original on 2021-11-22. Retrieved 2021-11-22.
    9. Marley, Mark S.; Fortney, Jonathan J.; Hubickyj, Olenka; Bodenheimer, Peter; Lissauer, Jack J. (2007-01-01). "On the Luminosity of Young Jupiters". The Astrophysical Journal. 655 (1): 541–549. arXiv:astro-ph/0609739. Bibcode:2007ApJ...655..541M. doi:10.1086/509759. ISSN 0004-637X. S2CID 7793365.
    10. "Giant Exoplanet Orbits Its Host Star Once Every 1.1 Million Years | Astronomy | Sci-News.com". Breaking Science News | Sci-News.com. Archived from the original on 2021-11-22. Retrieved 2021-11-22.
    11. Stelzer, B.; Bogner, M.; Magaudda, E.; Raetz, St. (2022). "Flares and rotation of M dwarfs with habitable zones accessible to TESS planet detections". Astronomy and Astrophysics. 665: A30. arXiv:2207.03794. Bibcode:2022A&A...665A..30S. doi:10.1051/0004-6361/202142088. S2CID 249662585.
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