When were the planets discovered? January 6, 2012 by Pamela Landy · Filed Under: Science Mercury, Mars, Venus, Jupiter, and Saturn were known from ancient times. Uranus was discovered in 1781, Neptune in 1846, and Pluto in 1930. Related PostsWho discovered the speed of light?How many ancient Norse settlements have been discovered in North America?Where was the Comstock Lode first discovered?What were the names of the 1970s British horror films that were inspired by 1950s E.C. Horror Comics?What were the names of the Piels Beer drinkers whose voices were provided by Bob Elliott and Ray Goulding?