At the end of the 19th century the existence of a planet beyond Neptune was in debate. In 1930, Pluto was discovered, but too far from the prediction.
In 1992 we found out that Pluto is actually a member of a huge belt of icy bodies orbiting beyond Neptune. Also in 1992 it has demonstrated that there never were real evidences for a Planet-X. In 2005, Iris was discovered and was considered has a possible 10th planet. In 2006, the “New Horizons” space mission is launched to the only planet not yet explored. On that same year, Pluto is demoted from planet to dwarf-planet. In 2015, “New Horizons”
reaches Pluto, and its moons, finding many surprises. And then, in 2016, new theories on the existence of another planet come back again. How is this possible? We’ll see about that.