COCONUTS-2b

Last updated
COCONUTS-2b
Coconuts-2b unwise.png
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 dateAugust 2011 (as a free-floating brown dwarf) [2]


July 2021 (as a planet) [3]
Direct imaging
Designations
WISEPA J075108.79-763449.6 [2]
Orbital characteristics
7,506.0 AU (1.12288×1012 km) [4] or ~0.1185 ly
1,101,369.9 years [4]
Star L 34-26
Physical characteristics
1.11+0.03
−0.04
  RJ
[5]
Mass 8±2  MJ [5]
log(g) = 4.19+0.18
−0.13
  cgs
[5]
Temperature 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]

    Contents

    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 it is more likely that the planet formed on its own via high entropy formation (aka hot-start process). [8] [9]

    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. [10]

    Another study found that their preferred model showed a metallicity that is lower than the host star, which is inconsistent with in-situ binary-like formation. 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] [8]

    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). [8]

    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 chemestry 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

    L 34-26
    COCONUTS-2 system unWISE.png
    L 34-26 (COCONUTS-2A) and its planetary companion in unWISE
    Observation data
    Epoch J2000.0       Equinox J2000.0
    Constellation Chamaeleon
    Right ascension 07h 49m 12.678s [11]
    Declination −76° 42 06.72 [11]
    Apparent magnitude  (V)11.3 [12]
    Characteristics
    Evolutionary stage Red dwarf
    Spectral type M3V [12]
    Astrometry
    Radial velocity (Rv)1.19±0.61 [13]  km/s
    Proper motion (μ)RA: -102.154  mas/yr [11]
    Dec.: -192.918  mas/yr [11]
    Parallax (π)91.8263 ± 0.0185  mas [11]
    Distance 35.519 ± 0.007  ly
    (10.890 ± 0.002  pc)
    Details
    Mass 0.37±0.02 [8]   M
    Radius 0.388±0.11 [8]   R
    Temperature 3,406±69 [8]   K
    Age 150–800 [8]   Myr
    Other designations
    L 34-26, COCONUTS-2A, WISEPA J075108.79-763449.6, 1RXS J074912.9-764202, 2MASS J07491271-7642065, ASAS J074912-7641.9, Gaia DR1 5213167326052013184, Gaia DR2 5213167330349528064, Gaia DR3 5213167330349528064, NLTT 18592 PM J07492-7642, RAVE J074912.7-764207, TIC 272232401, TYC 9381-1809-1, UCAC4 067-006518, USNO-B1.0 0132-00043434
    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 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. [14]

    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. [15] 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. [10]

    Related Research Articles

    <span class="mw-page-title-main">Teegarden's Star</span> M-type red dwarf in the constellation Aries

    Teegarden's Star is an M-type red dwarf star in the constellation Aries, 12.5 light-years from the Solar System. Although it is near Earth it is a dim magnitude 15 and can only be seen through large telescopes. This star was found to have a very large proper motion of about 5 arcseconds per year. Only seven stars with such large proper motions are currently known. Teegarden's Star hosts a planetary system with at least three planets.

    <span class="mw-page-title-main">Ross 128</span> Small star in constellation of Virgo

    Ross 128 is a red dwarf star in the equatorial zodiac constellation of Virgo, near β Virginis. The apparent magnitude of Ross 128 is 11.13, which is too faint to be seen with the unaided eye. Based upon parallax measurements, the distance of this star from Earth is 11.007 light-years, making it the twelfth closest stellar system to the Solar System. It was first cataloged in 1926 by American astronomer Frank Elmore Ross.

    GJ 1061 is a red dwarf star located 12 light-years from Earth in the southern constellation of Horologium. Even though it is a relatively nearby star, it has an apparent visual magnitude of about 13, so it can only be seen with at least a moderately-sized telescope.

    <span class="mw-page-title-main">Rogue planet</span> Planets not gravitationally bound to a star

    A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf.

    <span class="mw-page-title-main">Gliese 876</span> Star in the constellation Aquarius

    Gliese 876 is a red dwarf star 15.2 light-years away from Earth in the constellation of Aquarius. It is one of the closest known stars to the Sun confirmed to possess a planetary system with more than two planets, after GJ 1061, YZ Ceti, Tau Ceti, and Wolf 1061; as of 2018, four extrasolar planets have been found to orbit the star. The planetary system is also notable for the orbital properties of its planets. It is the only known system of orbital companions to exhibit a near-triple conjunction in the rare phenomenon of Laplace resonance. It is also the first extrasolar system around a normal star with measured coplanarity. While planets b and c are located in the system's habitable zone, they are giant planets believed to be analogous to Jupiter.

    HD 114386 is a star with a pair of orbiting exoplanets in the southern constellation of Centaurus. It has an apparent visual magnitude of 8.73, which means it cannot be viewed with the naked eye but can be seen with a telescope or good binoculars. Based on parallax measurements, the system is located at a distance of 91 light years from the Sun. It is receding with a radial velocity of 33.4 km/s. The star shows a high proper motion, traversing the celestial sphere at an angular rate of 0.318 arcsec yr−1.

    <span class="mw-page-title-main">Groombridge 34</span> Binary star system in the constellation of Andromeda

    Groombridge 34 is a binary star system in the northern constellation of Andromeda. It was listed as entry number 34 in A Catalogue of Circumpolar Stars, published posthumously in 1838 by British astronomer Stephen Groombridge. Based upon parallax measurements taken by the Gaia spacecraft, the system is located about 11.6 light-years from the Sun. This positions the pair among the nearest stars to the Solar System.

    TZ Arietis is a red dwarf in the northern constellation of Aries. With a normal apparent visual magnitude of 12.3, it is too faint to be seen by the naked eye, although it lies relatively close to the Sun at a distance of 14.6 light-years. It is a flare star, which means it can suddenly increase in brightness for short periods of time.

    <span class="mw-page-title-main">HD 189733</span> Binary star system in the constellation Vulpecula

    HD 189733, also catalogued as V452 Vulpeculae, is a binary star system 64.5 light-years away in the constellation of Vulpecula. The primary star is suspected to be an orange dwarf star, while the secondary star is a red dwarf star. Given that this system has the same visual magnitude as HD 209458, it promises much for the study of close transiting extrasolar planets. The star can be found with binoculars 0.3 degrees east of the Dumbbell Nebula (M27).

    <span class="mw-page-title-main">Planetary-mass object</span> Size-based definition of celestial objects

    A planetary-mass object (PMO), planemo, or planetary body is, by geophysical definition of celestial objects, any celestial object massive enough to achieve hydrostatic equilibrium, but not enough to sustain core fusion like a star.

    <span class="mw-page-title-main">Kepler-444</span> Triple star system in the constellation of Lyra

    Kepler-444 is a triple star system, estimated to be 11.2 billion years old, approximately 119 light-years (36 pc) away from Earth in the constellation Lyra. On 27 January 2015, the Kepler spacecraft is reported to have confirmed the detection of five sub-Earth-sized rocky exoplanets orbiting the main star. The star is a K-type main sequence star. All of the planets are far too close to their star to harbour life forms.

    <span class="mw-page-title-main">LTT 1445</span> Star system in the constellation Eridanus

    LTT 1445 is a triple M-dwarf system 22.4 light-years distant in the constellation Eridanus. The primary LTT 1445 A hosts two exoplanets—one discovered in 2019 that transits the star every 5.36 days, and another found in 2021 that transits the star every 3.12 days, close to a 12:7 resonance. As of October 2022 it is the second closest transiting exoplanet system discovered, with the closest being HD 219134 bc.

    Qatar-2 is a K-type main-sequence star about 595 light-years away in the constellation of Virgo. The star is much older than Sun, and has a concentration of heavy elements similar to solar abundance. The star features a numerous and long-lived starspots, and belongs to a peculiar variety of inflated K-dwarfs with strong magnetic activity inhibiting internal convection.

    WASP-69, also named Wouri, is a K-type main-sequence star 164 light-years away. Its surface temperature is 4782±15 K. WASP-69 is slightly enriched in heavy elements compared to the Sun, with a metallicity Fe/H index of 0.10±0.01, and is much younger than the Sun at 2 billion years. The data regarding starspot activity of WASP-69 are inconclusive, but spot coverage of the photosphere may be very high.

    <span class="mw-page-title-main">Cool Companions on Ultrawide Orbits</span>

    The COol Companions ON Ultrawide orbiTS (COCONUTS) program is a large-scale survey for wide-orbit planetary and substellar companions considered the first survey of this type of celestial bodies. In 2021, the team announced COCONUTS-2b, the closest exoplanet directly imaged ever. The program is a dedicated large-scale search for wide-orbit giant planets and brown dwarf companions, targeting a sample of 300,000 stars. By using multi-wavelength photometry and multi-epoch astrometry, astronomers are able to assess the candidates' companionship and ultracool nature.

    LHS 3844 is a red dwarf star located 48.5 light-years away from the Solar System in the constellation of Indus. The star has about 15% the mass and 19% the radius of the Sun. It is a relatively inactive red dwarf with a slow rotation period of about 128 days, though UV flares have been observed. LHS 3844 is orbited by one known exoplanet.

    TOI-1227 b is one of the youngest transiting exoplanets discovered, alongside K2-33b and HIP 67522 b. The exoplanet TOI-1227 b is about 11±2 million years old and currently 9.6 R🜨 large. It will become a 3-5 R🜨 planet in about 1 billion years, because the planet is still contracting. TOI-1227 b orbits its host star every 27.36 days.

    References

    1. 1 2 "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. 1 2 3 4 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.
    3. 1 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.
    4. 1 2 "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.
    5. 1 2 3 4 5 6 7 8 Zhang, Zhoujian; Mukherjee, Sagnick; Liu, Michael C.; Fortney, Jonathan J.; Mader, Emily; Best, William M. J.; Dupuy, Trent J.; Leggett, Sandy K.; Karalidi, Theodora (2024-10-14). "Disequilibrium Chemistry, Diabatic Thermal Structure, and Clouds in the Atmosphere of COCONUTS-2b". arXiv: 2410.10939 .
    6. "Exoplanet-catalog". Exoplanet Exploration: Planets Beyond our Solar System. Archived from the original on 2021-11-22. Retrieved 2021-11-22.
    7. 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.
    8. 1 2 3 4 5 6 7 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.
    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. 1 2 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. arXiv: 2404.14324 . Bibcode:2024ApJ...967..147M. doi: 10.3847/1538-4357/ad3f1d .
    11. 1 2 3 4 5 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv: 2208.00211 . Bibcode:2023A&A...674A...1G. doi: 10.1051/0004-6361/202243940 . S2CID   244398875. Gaia DR3 record for this source at VizieR.
    12. 1 2 Martin, Pierre-Yves (2021). "Planet COCONUTS-2 b". Extrasolar Planets Encyclopaedia . Retrieved 2023-11-28.
    13. "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2023-11-28.
    14. "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.
    15. 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.