The first planet discovered that does not rotate around a star
It is very difficult to identify planets that move independently in the galaxy because the do not give out light and cannot be seen as is the case of other planets that rotates around stars. However, due to new methodology it has been possible to start detecting some rogue planets as it is the case with 

SIMP J013656.5 +093347.
This celestial body, located in the constellation Pisces, is defined as a brown dwarf but can be also considered a giant rogué planet.  
Brown dwarfs, also called "failed stars", are small mass stars that do not possess enough mass to start nuclear reactions, They are larger than planets, but not quite large enough to fuse hydrogen, the ways stars do.  

Rogue planets are planets that are not tied to a star and their masses are smaller than typical brown dwarfs, and for this reason SIMP J013656.5 +093347 may be classified as a rogue planet.

It belongs to the spectral class T2.5 and its position shifts due to its proper motion annually by about 1.24 arcsec with a position angle of about 90°.

This rogue planet (brown dwarf) provided the first evidence for periodic variability flux variations among T dwarfs. This has been interpreted as a signature of weather patterns coming in and out of view over the object's 2.4h rotation period.

The shape of this lightcurve evolves over timescales of days, which has been interpreted as a sign of evolution of the cloud patterns in its atmosphere.

In 2017, it was announced that the object's mass may be as low as 12.7 Jupiter masses and should be considered a rogue planet rather than a Brown Dwarf as it seems to be a member of the relatively young, 200 million-year-old Carina-Near stellar moving group.

In 2018, astronomers noted, "Detecting SIMP J01365663+0933473 with the VLA through its auroral radio emission, also means that we may have a new way of detecting exoplanets, including the elusive rogue ones not orbiting a parent star ... This particular object is exciting because studying its magnetic dynamo mechanisms can give us new insights on how the same type of mechanisms can operate in extrasolar planets - planets beyond our Solar System ... We think these mechanisms can work not only in brown dwarfs, but also in both gas giant and terrestrial planets.