Astronomy: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 by | Zhoujian Zhang Michael Liu Zach Claytor William Best Trent Dupuy Robert Siverd[1] |
| Discovery date | August 2011 (as a free-floating brown dwarf)[2]
|
| Direct imaging | |
| Designations | |
| WISEPA J075108.79-763449.6[2] | |
| Orbital characteristics | |
| 7,506+5,205 −2,060 astronomical unit|AU[4] (1.123×1012 km) | |
| Orbital period | 1.1+1.3 −0.4×106[4] years |
| Star | L 34-26 |
| Physical characteristics | |
| Mean radius | 1.11+0.03 −0.04 RJ[5] |
| Mass | 8±2 MJ[5] |
| log(g) = 4.19+0.18 −0.13 cgs[5] | |
| Physics | 483+44 −53 K[5] |
Spectral type | T9.5±0.5[5] |
COCONUTS-2 b is a gas giant exoplanet that orbits the M-type star L 34-26. With a mass of 8 Jupiters,[5] it takes over one million years to complete one orbit around the star orbiting 7,506 AU away from it.[1]
The planet was discovered in 2011 and was initially identified as a T9 free-floating brown dwarf WISEPA J075108.79−763449.6.[2] During the COol Companions ON Ultrawide orbiTS (COCONUTS) survey, its association with L 34-26 was announced in 2021.[6] At a distance of 35.5 light-years (10.9 parsecs), COCONUTS-2b was the closest directly imaged exoplanet to Earth[7] until Epsilon Indi Ab was imaged in 2024.
Proposed formation scenarios
The researchers found that it is unlikely that COCONUTS-2b was formed inside the protoplanetary disk of the host star and may instead have formed separately.[4][8]
The peculiar properties of COCONUTS-2b could be explained with different scenarios as proposed by Marocco et al. in 2024. The properties could be explained by a non-solar carbon-to-oxygen ratio, meaning that it formed inside a disk around L 34–26. In this scenario the most likely way COCONUTS-2b got in a higher orbit is by a stellar fly-by of two binaries or two planetary systems. In the second scenario L 34-26 is not actually young, but mimics youth due to tidal and/or magnetic interactions with an unseen companion. In this scenario COCONUTS-2b would be an old brown dwarf. In a third scenario COCONUTS-2b could be a captured old brown dwarf. This is however seen as unlikely due to the stellar fly-by requiring a low velocity.[9]
Another study in 2024 found that the metallicity of the planet is lower than that of the host star, which is inconsistent with it forming on its current location, like a binary system. Only their third-preferred model is consistent with a binary-like formation, because in this model the metallicity of host star and planet agreed.[5]
Atmosphere
The planet's spectral type suggests high amounts of methane, water vapor and low amounts of carbon monoxide in the atmosphere of COCONUTS-2b. It might also have both clouds and a non-equilibrium process in its atmosphere.[2][4]
Due to its large orbital separation, COCONUTS-2b is a great laboratory to study the atmosphere and composition of young gas-giant exoplanets.[3] Astronomers estimate the planet's temperature to be around 434 K (161 °C; 322 °F).[4]
Observations with Gemini/Flamingos-2 showed a spectral type of T9.5±0.5, near the T/Y transition. The spectrum is also more consistent with disequilibrium chemistry and the presence of clouds. Additionally the atmosphere shows a diabatic thermal structure, meaning the pressure-temperature profile is non-adiabatic. Adiabatic means here an increase of the temperature with pressure. The observation also indicate a sub- or near-solar metallicity.[5]
Host star
260px L 34-26 (COCONUTS-2A) and its planetary companion in unWISE | |
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Chamaeleon |
| Right ascension | 07h 49m 12.678s[10] |
| Declination | −76° 42′ 06.72″[10] |
| Apparent magnitude (V) | 11.3[11] |
| Characteristics | |
| Evolutionary stage | Red dwarf |
| Spectral type | M3V[11] |
| Astrometry | |
| Radial velocity (Rv) | 1.19±0.61[12] km/s |
| Proper motion (μ) | RA: -102.154[10] mas/yr Dec.: -192.918[10] mas/yr |
| Parallax (π) | 91.8263 ± 0.0185[10] mas |
| Distance | 35.519 ± 0.007 ly (10.890 ± 0.002 pc) |
| Details | |
| Mass | 0.37±0.02[4] M☉ |
| Radius | 0.388±0.011[4] R☉ |
| Temperature | 3,406±69[4] K |
| Age | 150–800[4] Myr |
| Other designations | |
L 34-26, COCONUTS-2A, WISEPA J075108.79-763449.6, 1RXS J074912.9-764202, 2MASS J07491271-7642065, NLTT 18592, TIC 272232401, TYC 9381-1809-1, UCAC4 067-006518 | |
| Database references | |
| SIMBAD | data |
L 34–26, also known as COCONUTS-2A and TYC 9381–1809–1, is a M3-type dwarf star located 35 light-years from Earth, 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.[13]
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.[14] The star is seen almost equator-on with i = 81.8±5.8 deg and might belong to the proposed Ursa Major corona, which is 400 million years old.[9]
Gallery
-
The COCONUTS-2 system with unWISE -
The planet COCONUTS-2b with Gemini-South -
Allwise image by the discoverers, showing planet COCONUTS-2b
References
- ↑ 1.0 1.1 "Massive COCONUTS exoplanet discovery led by UH grad student | University of Hawaiʻi System News". University of Hawaiʻi News (University of Hawaiʻi at Mānoa). https://www.hawaii.edu/news/2021/07/27/massive-coconuts-exoplanet-discovery-uh-grad-student/.
- ↑ 2.0 2.1 2.2 2.3 Kirkpatrick, J. Davy; Cushing, Michael C.; Gelino, Christopher R.; Griffith, Roger L.; Skrutskie, Michael F.; Marsh, Kenneth A.; Wright, Edward L.; Mainzer, A. et al. (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. doi:10.1088/0067-0049/197/2/19. ISSN 0067-0049. Bibcode: 2011ApJS..197...19K. https://ui.adsabs.harvard.edu/abs/2011ApJS..197...19K.
- ↑ 3.0 3.1 Kooser, Amanda. "Massive exoplanet 'Coconuts-2b' could help reveal the secrets of young gas giants" (in en). CNET. https://www.cnet.com/news/meet-coconuts-2b-an-exoplanet-with-six-times-the-mass-of-jupiter/.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 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. doi:10.3847/2041-8213/ac1123. ISSN 0004-637X. Bibcode: 2021ApJ...916L..11Z.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Zhang, Zhoujian et al. (2025). "Disequilibrium Chemistry, Diabatic Thermal Structure, and Clouds in the Atmosphere of COCONUTS-2b". The Astronomical Journal 169 (1). doi:10.3847/1538-3881/ad8b2d. Bibcode: 2025AJ....169....9Z.
- ↑ "Exoplanet-catalog". https://exoplanets.nasa.gov/exoplanet-catalog/7945/coconuts-2-b/.
- ↑ Siegel, Ethan. "Astronomers Go Nuts For Closest Exoplanet Directly Imaged Ever: COCONUTS-2b" (in en). https://www.forbes.com/sites/startswithabang/2021/08/02/astronomers-go-nuts-for-closest-exoplanet-directly-imaged-ever-coconuts-2b/.
- ↑ 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. doi:10.1086/509759. ISSN 0004-637X. Bibcode: 2007ApJ...655..541M.
- ↑ 9.0 9.1 Marocco, Federico; Kirkpatrick, J. Davy; Schneider, Adam C. et al. (2024-04-22). "Thirteen New M Dwarf + T Dwarf Pairs Identified with WISE/NEOWISE". The Astrophysical Journal 967 (2): 147. doi:10.3847/1538-4357/ad3f1d. Bibcode: 2024ApJ...967..147M.
- ↑ 10.0 10.1 10.2 10.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 11.0 11.1 Martin, Pierre-Yves (2021). "Planet COCONUTS-2 b" (in en). Extrasolar Planets Encyclopaedia. https://exoplanet.eu/catalog/coconuts_2_b--7920/. Retrieved 2023-11-28.
- ↑ "Simbad - Object view". https://simbad.cds.unistra.fr/mobile/object.html?object_name=COCONUTS-2A.
- ↑ "Giant Exoplanet Orbits Its Host Star Once Every 1.1 Million Years | Astronomy | Sci-News.com" (in en-US). http://www.sci-news.com/astronomy/coconuts-2b-exoplanet-09922.html.
- ↑ 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. doi:10.1051/0004-6361/202142088. Bibcode: 2022A&A...665A..30S.
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