Almost all planets have a regular orbit around a sun or host star. However, a rogue planet is one that has either left its regular orbit or never had a regular orbit to begin with and is now orbiting the galaxy itself.
In 2012 astronomers thought they had found one of the closest rogue planets ever to be discovered, but there were things that didn’t quite add up about the giant object roughly four to seven times bigger than Jupiter.
It was located a mere 100 light years away, which sounds like a long way to the average person, but to astronomers, this makes the rogue planet extremely close. The object was determined to be a candidate for “rogue planet” classification after it was proven that it was smaller than the classification of brown dwarfs which are more than 13 times larger than Jupiter.
It was also discovered that it was moving with a larger group which was orbiting our galaxy together. Based on this information it was determined that the group of objects were approximately 50 to 120 million years old, which in the grand scheme of things is relatively young.
The scientific community was not in full agreement of the object’s classification as a rogue planet, however. There were two main problems that hadn’t been addressed. First, was the fact that there was no evidence that it had ever been a part of any solar system. Second, it was later proven that based on the object’s movement it was not a part of the larger group, and either had very low gravity or extremely high metal content, which makes it harder to determine the object’s mass. Thus it could be considered a brown dwarf with a higher mass.
Based on these findings there are two possible outcomes, either it is a young rogue planet less than 13 times the mass of Jupiter, or a much older (2 to 3 billion years) brown dwarf up to 40 times the mass of Jupiter.
There is also a third possibility, perhaps the most interesting, that the object cannot be classified as either and is a combination of both that needs an entirely new classification.
Luckily, because it is so close it can be continually observed, and with a little more study a determination can be reached.