Enigmatic Planet Nine may have been seen by telescope in the 1980s. There is an ongoing debate about whether a huge "super-Earth" lurks in the far reaches of our solar system – but we may actually have observed it almost 40 years ago

https://www.newscientist.com/article/2297376-enigmatic-planet-nine-may-have-been-seen-by-telescope-in-the-1980s/