The mysterious world – dubbed Planet Nine – is about 10 times bigger than the Earth and thought to be gaseous.
Scientists believe it traces a highly elongated orbit and takes between 10,000 and 20,000 years to make just one journey around the sun.
Planet Nine is, on average, about 20 times further from the sun than Neptune, which orbits at a distance of about 2.8 billion miles.
Since the staggering discovery, UFO hunters around the world have speculated that aliens could be living on the planet.
Writing on social media, Donn Morgan Kipgen said Planet Nine may be "harbouring" extra-terrestrial life.
And Jason Tammemagi tweeted: "If Planet Nine doesn't have ancient alien structures, I will be really disappointed."