* Uranus: Discovered in 1781 by William Herschel.

* Neptune: Discovered in 1846 by Urbain Le Verrier and John Couch Adams (though neither actually saw it).

* Pluto: Discovered in 1930 by Clyde Tombaugh.

It's important to note that Pluto is no longer considered a planet but is now classified as a dwarf planet.

The other planets in our solar system (Mercury, Venus, Mars, Jupiter, Saturn) were all known to ancient civilizations.