“Planet 9 this invisible world is currently only theoretical but since it was first proposed in 2016 evidence has been stacking up that it may be out there “
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Not true. Planet 10 (or planet x) was proposed back in the 1980s. There was an article in OMNI or astronomy magazine (I forget which) that proposed that they had measured some gravitational anomalies that can only be explained by the presence of another planet. They called it planet 10 then because pluto was still considered a planet at that time.
But is this elusive Planet really a planet or is it another Celestial body?
You can see the question like that comes up , because Pluto had been called the ninth planet for so many decades , and then it was downgraded.
So perhaps another celestial object is out there , but is it really a planet?