In what year was each planet in your solar system discovered?

Answer 1

It depends on the planet. here is a list of all planets including dwarf planets with their years of discovery:

1. Mercury (unknown, but first mentioned in about 265 BCE, and first observed by telescope in 1639)
   
2. Venus (unknown, but first observed through a telescope in 1610)
   
3. Earth
   
4. Mars (unknown, but first recorded in 1534 BCE in Egypt, first observed by telescope in 1659)
   
5. Ceres (January 1, 1801)
6. Jupiter (about the 8th Century BCE or older, but first observed through a telescope in1610)
   
7. Saturn (unknown, but first observed through a telescope in 1610)
   
8. Uranus (known in ancient times as a star, first observed as a planet on March 13, 1781)
   
9. Neptune (September 23, 1846...however Galileo may have observed it in 1613)
10. Pluto (February 18, 1930)
11. Haumea (December 28, 2004)
12. Makemake (March 31, 2005)
13. Eris (January 5, 2005)

Answer 2

Mercury, Venus, Earth, Mars, Jupiter, Saturn: "Naked-eye" planets; known since the beginning of time. Uranus: 1781Neptune: 1846 Pluto: 1930