Notice that in the telegram from Lowell Observatory — the stuff that comes after the colon — nobody calls it a planet – not yet. Why? Because the astronomers at Lowell know they’ve got something weird. The object they’ve discovered on February 18 is definitely retrograding — that is, it’s definitely in orbit around the sun. But in size, color, and composition, the object is not at all what they expected.
They’re further faced with a weird dilemma – that the object is just about where Percival Lowell’s math suggested it would be. But it’s too small to have been discovered through its perturbative effects on Saturn, Uranus, and Neptune. How can this be?