![](/static/253f0d9b/assets/icons/icon-96x96.png)
![](https://lemmy.world/pictrs/image/44bf11eb-4336-40eb-9778-e96fc5223124.png)
Pluto was discovered because the orbit of Neptune didn’t match predictions, so astronomers decided that there must be a ninth planet out there. It was very close to where the math predicted it would be.
It turned out later that Pluto was much, much smaller than at first thought, and couldn’t be the 9th planet. It then turned out that the mass of Neptune was greater than expected, and the orbit actually matched expectations without the need for a 9th planet.
Same