A good article from the BBC, that goes back to the days of Percival Lowell, who spent a fortune of his own money, to build an observatory to find intelligent life on Mars.
He was later obsessed with finding Planet X that was distorting Neptune's orbit around the Sun.
When he died in 1916 he left in his will a $1Miilion to keep his telescope searching for Planet X, no luck, but his telescope did discover Pluto in 1930.
Fast forward to 2021 and scientists are still searching for Planet X.
https://www.bbc.com/future/article/2...ists-cant-find