There's a bit of a misunderstanding here. There haven't been any new planets discovered in our solar system since the early 1800s. We currently recognize eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Here's the breakdown:

* Uranus: Discovered in 1781 by William Herschel.

* Neptune: Discovered in 1846 by Urbain Le Verrier and John Couch Adams (though neither actually saw it, their calculations led to its discovery).

Since then, we've reclassified Pluto and other objects as dwarf planets.