2004

January

• January 2: Stardust visits the comet Wild 2.

February

• February 17: The Minor planet Orcus is discovered.

June

• June 1: Methone and Pallene are discovered.

July

• July 1: Cassini-Huygens enters orbit of Saturn.

August

• August 3: MESSENGER is launched.

September

• September 8: Genesis lands back on Earth.
• September 22: Salacia is discovered.

October

• October 24: Polydeuces is discovered.

December

• December 12: S/2004 S 7, Fornjot, Farbauti, Aegir, Bebhionn, S/2004 S 12, S/2004 S 13, Hati, Bergelmir, S/2004 S 20, and S/2004 S 21 are discovered.
• December 13: Fenrir, S/2004 S 17, S/2004 S 22, S/2004 S 23, S/2004 S 24, S/2004 S 25, S/2004 S 26, S/2004 S 27, S/2004 S 28, S/2004 S 29, S/2004 S 30, S/2004 S 31, S/2004 S 32, S/2004 S 33, S/2004 S 34, S/2004 S 35, S/2004 S 36, S/2004 S 37, S/2004 S 38, S/2004 S 39, and Bestla are discovered.

• December 28: Michael Brown discovers the Dwarf planet named Haumea.