New investigations of mysterious lonely planet

An object with code  CFBDSIR 2149-0403  was detected in 2012 by team of astronomers led by Philippe Delorme. It was initially identified as ultracold brown dwarf, part of the AB Doradus moving group - tight group of young stars with similar parameters, indicating that they formed simultaneously. 

CFBDSIR 2149-0403 is located about 20 parsecs (62,5 light years) from Earth, its mass is estimated between 2 - 12 Jupiter masses (13 Jupiter masses - fusion threshold when brown dwarf turns to real star). Spectral observations show surface temperature about 700 K (426 C) and indicate traces of methan and water in the atmosphere.

New investigation, published March 2 in a paper on arxiv.org by the same group, shows that CFBDSIR 2149-0403 does not belong to the group. It is isolated body - planet without sun, or ultracold brown dwarf with high metallicity.

Image:  ESO/L. Calçada/P. Delorme/R. Saito/VVV Consortium. Isolated planet in infrared light

The data, obtained from the Very Large Telescope (VLT) and Spitzer space telescope prove that CFBDSIR 2149-0403 never was a part of any star system, ejected from it by another star gravity. It is free floating body with unusual properties, such as high metallicity.

There is however another hypothesis - that CFBDSIR 2149-0403 is a part of unresolved binary system, in which smaller companion is a planet. Such systems exist: a very cold pair of brown dwarfs with surface temperature no more than 100 C was discovered with the same VLT.  it could even have water clouds in its atmosphere .

For further reading: https://phys.org/news/2017-03-mysterious-isolated-astronomers.html

https://phys.org/news/2011-03-cool-pair-brown-dwarfs.html#nRlv