Timeline of Discovery of Solar System Planets and Their Moons

17th century
Date	Name	Image	Permanent designation	Discoverer(s) and notes
1610s
o: January 7, 1610 p: March 13, 1610	Ganymede		Jupiter III	Galileo. The Galilean moons. The Galilean satellites were the first celestial objects that were confirmed to orbit an object other than the Sun or Earth. Galileo saw Io and Europa as a single point of light on January 7, 1610; they were seen as separate bodies the following night.
o: January 7, 1610 p: March 13, 1610	Callisto		Jupiter IV
o: January 8, 1610 p: March 13, 1610	Io		Jupiter I
o: January 8, 1610 p: March 13, 1610	Europa		Jupiter II
1650s
o: March 25, 1655 p: March 5, 1656	Titan		Saturn VI	Huygens. He first "published" his discovery as an anagram, sent out on 13 June 1655; later published in pamphlet form as De Saturni luna Observatio Nova and in full in Systema Saturnium (July 1659).
1670s
o: October 25, 1671 p: 1673	Iapetus		Saturn VIII	Cassini
o: December 23, 1672 p: 1673	Rhea		Saturn V	Cassini
1680s
o: March 21, 1684 p: April 22, 1686	Tethys		Saturn III	Cassini. Together with his previous two discoveries, Cassini named these satellites Sidera Lodoicea. In his work Kosmotheôros (published posthumously in 1698), Christiaan Huygens relates "Jupiter you see has his four, and Saturn his five Moons about him, all plac’d in their Orbits."
o: March 21, 1684 p: April 22, 1686	Dione		Saturn IV
Date	Name	Image	Permanent designation	Discoverer(s) and notes

Timeline of Discovery of Solar System Planets and Their Moons - 17th Century