The so-called "rogue" planet does not revolve around a star, but instead rotates around the galactic center in interstellar space.
The massive planet is 20 light years away from Earth.
"This object is right at the boundary between a planet and a brown dwarf, or 'failed star, ' and is giving us some surprises that can potentially help us understand magnetic processes on both stars and planets", said Melodie Kao, an astronomer at Arizona State University.
The recently discovered planetary mass was originally found in 2016 but was mistaken for a brown dwarf planet. The object is about twelve times as massive as Jupiter and has a surprisingly powerful magnetic field.
It was detected using US National Science Foundation's Karl G Jansky Very Large Array (VLA) telescope.
In the first radio-telescope detection of a planetary-mass object beyond our solar system, astronomers have found the odd celestial body has 12.7 times the mass of Jupiter.
Brown dwarfs are objects too massive to be considered planets, yet not massive enough to sustain nuclear fusion of hydrogen in their cores - the process that powers stars.
The unusual object sits in a grey area between a star and a planet, and was originally classed as a "brown dwarf" - a failed star.
Both its mass and the enormous strength of its magnetic field, which is more than 200 times stronger than Jupiter's, challenge what scientists know about the variety of astronomical objects found in the depths of space.
Despite its weight, the newly discovered planet has a radius only 1.2 times that of Jupiter, the study said. Researchers aren't sure how brown dwarf auroras happen - "rogue" planets like these lack a nearby star's solar wind for the magnetic field to interact with.
Kao led this study while a graduate student at California Institute of Technology (Caltech).
Once more data was obtained, the idea that SIMP J01365663+0933473 was a brown dwarf was scrapped.
Brown dwarf masses are notoriously hard to measure, and at the time, SIMP0136 was thought to be an old and much more massive brown dwarf.
Compared to the Sun's 5,500-degree-Celsius surface temperature (9,932 degrees Fahrenheit), it's relatively cool, coming in with a surface temperature of 825 degrees Celsius (around 1517 degrees Fahrenheit).
The team is particularly excited by the new research because it relies in part on radio observations of the object's auroras - which means that radio telescopes may be able to identify new planets by their auroras.