New Horizons Spacecraft approaching Pluto
Pluto was formerly defined as the ninth and smallest planet in our solar system but on August 24, 2006 it was redefined as a dwarf planet, and the total number of planets was reduced to eight. This happened because astronomers discovered several similarly sized objects in a belt just past Neptune, known as the Kuiper belt.
I remember growing up as a kid, having the notion that there are nine planets in our solar system rammed into my head. Well, even scientific claims like the number of planets is subject to change. Although I must admit, I still think of Pluto as a planet. And all that other similarly sized stuff, well, it’s just stuff. (The power of naming, I guess).