Kao's team used a radio astronomy observatory located in central New Mexico called - fittingly - the "Very Large Array" (VLA) to pick up its magnetic activity and study it. It appears to be traveling through space alone.
"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", Melodie Kao, leader of the study and Hubble postdoctoral fellow at Arizona State University, said in a press release.
A brown dwarf is an object too large to be a planet, but isn't big enough to sustain the nuclear fusion of hydrogen in its core that is typical of stars.
Although the planet is roaming the galaxy by itself, without a companion star to orbit, its surface is quite hot judging by planetary standards. Some brown dwarfs have powerful auroras like those seen around the poles of Earth, Jupiter and Saturn caused by the interactions of a planet's magnetic field and the electrically charged solar wind.
Initially believed to be a brown dwarf star, the peculiar celestial object, boasting a suite of unusual physical traits, turned out to be a planet after all. It also has a strong magnetic field, 200 times the strength of Jupiter.
An artist's impression of an unusual body 12 times more massive than Jupiter some 20 light years away featuring an aurora generated by a magnetic field 200 times more powerful than Jupiter's.
The object, which has been named SIMP J01365663+0933473, was first detected in 2016, but was thought to be a brown dwarf.
Despite its weight, the newly discovered planet has a radius only 1.2 times that of Jupiter, the study said.
Simultaneously, the Caltech team that originally detected its radio emission in 2016 had observed it again in a new study at even higher radio frequencies and confirmed that its magnetic field was even stronger than first measured.
Such a strong magnetic field "presents huge challenges to our understanding of the dynamo mechanism that produces the magnetic fields in brown dwarfs and exoplanets and helps drive the auroras we see", said Gregg Hallinan, of Caltech.
The VLA observations provided both the first radio detection and the first measurement of the magnetic field of a possible planetary mass object beyond our solar system. "We think these mechanisms can work not only in brown dwarfs, but also in both gas giant and terrestrial planets", Kao said. They are reporting their findings in the Astrophysical Journal.
Dubbed SIMP J01365663+0933473, this peculiar exoplanet has baffled astronomers because it seems to be floating around without being attached to a parent star, which qualifies it as a "rogue", notes the National Radio Astronomy Observatory.