The name interstellar planet refers to a planet (in the sense that humans know of a planet) that is not connected to a Solar System, but rather floating around in interstellar space.
What does the name interstellar planet refer to?
Scientists agree that interstellar planets formed as regular planets, in the sense that Earth and Jupiter are planets, but that at some point during their creation, part of the planet jettisoned off into outer space and is no longer part of the system from which it was formed. Scientists agree on this process of formation, but they don’t agree on the terminology with which it is named.
The definition of a planet is a geological mass that orbits around a star like our sun. Since interstellar planets are not orbiting around a star, their own sun, they cannot be called a planet, interstellar or otherwise. Hence, the debate lies in the terminology used to describe interstellar planets, not in their existence.
In the 1950s there was a book (science fiction) that brought the idea of planets being ripped out of their solar systems by a change in space. In the book, the Earth was ripped away from the sun, with all sorts of adventurous disaster following suit.
Of course, this type of book is science fiction, but the principle of a planet being knocked out of its orbit and even being knocked out of its own solar system entirely is completely valid. If this were to happen to the Earth, no life would survive it, but the planet, itself, would survive.
It would not survive in its present state, not with oceans and all, but the core of the Earth, the inner geological mass would survive, at least for a while, ejected out beyond the confines of our solar system.
So, while the name interstellar planet needs some work before it will be widely accepted by astronomers and scientists of the most exacting kind, they don’t seem to need more evidence that interstellar planets exist.
The question is how to change a name such as this? If the Mars was a planet at some point, and everyone agreed that it was a planet (unlike poor Pluto), how can the name ‘planet’ be ripped away from it when its orbit changes? Sure, one of the defining characteristics of a planet is that it revolves around a star, but shouldn’t the term ‘planet’ be modified slightly, such that a planet could be a mass that orbits, or once orbited, around an identified star If that were the case, interstellar planets could still be interstellar planets and they could also remain planets. It seems quite odd to rip the title ‘planet’ away from a celestial body that has been a planet for millions of years.
As a star goes through its life phases, its name changes slightly; however, it is still a star. Couldn’t the name ‘interstellar planet’ refer to a planet that was once a planet and then was ejected out of orbit around its star and has become an interstellar planet That would, after all, be the exact meaning of ‘interstellar planet’. ‘
Inter’ meaning ‘between’ and ‘stellar’ meaning ‘stars’, such that an interstellar planet is a planet that is between stars. To some, the name is perfectly logical when taken as a full compound and analyzed as three parts that all come together to form the concept of what an interstellar planet actually is.
However, some astronomers cannot get past the word planet being in the compound name. For these scientists, the discussion stops there, because a planet can only be a planet if it’s orbiting a star; that’s where the distinction ‘interstellar’ comes into play.