Discovery | |
---|---|
Discovered by | Zhoujian Zhang Michael Liu Zach Claytor William Best Trent Dupuy Robert Siverd [1] |
Discovery date | August 2011
[2] July 2021 [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 (~0.03633 pc) | |
1101369.9 years [4] | |
Star | L 34-26 |
Physical characteristics | |
Mean radius | 1.12±0.04 RJ [5] |
Mass | 6.3+1.5 −1.9 MJ [6] [4] |
4.11+0.11 −0.18 dex [6] | |
Temperature | 434 ± 9 K [6] |
Spectral type | T9 |
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 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. [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). [6] [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]
The planet has a spectral type of T9, based on a low signal-to-noise near-infrared spectrum with Magellan/FIRE. [2] [6] 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. [6]
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). [6]
Observation data Epoch J2000.0 Equinox J2000.0 | |
---|---|
Constellation | Chamaeleon |
Right ascension | 07h 49m 12.71s |
Declination | +76° 42′ 02.5″ |
Apparent magnitude (V) | 11.3 [11] |
Characteristics | |
Evolutionary stage | Red dwarf |
Spectral type | M3V [12] |
Astrometry | |
Radial velocity (Rv) | 1.19 [13] km/s |
Proper motion (μ) |
RA: -102.154
mas/
yr
[13] Dec.: -192.918 mas/ yr [13] |
Parallax (π) | 91.8263 mas [13] |
Distance | 35.5±0.0065
[6]
ly (10.89±0.002 pc) |
Details | |
Mass | 0.37±0.02 [6] M☉ |
Radius | 0.388±0.11 [6] R☉ |
Temperature | 3,406±69 [6] K |
Age | 475±325 [6] 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]