The year 2004 in science had some important events, listed below.

• January 3 - NASA's Spirit rover lands on Mars.
• January 24 - NASA's Opportunity rover lands on Mars.
• March 2 - NASA says that the area where their Mars probe Opportunity landed shows unmistakable signs of contact with water in the geological past.
• March 4 - NASA's Spirit finds proof of past contact with water in volcanic rocks on Mars.
• April 20 - NASA launched the Gravity Probe B to test the general theory of relativity of Einstein.
• October 27 - The Homo floresiensis has been discovered by Peter Brown, Michael Morwood and their colleagues.
• September 13 - Astronomers from the European Southern Observatory announce images that seem to show a planet orbiting a brown dwarf about 230 light years away.
• November 15 - The SMART-1 space probe reaches orbit around the Moon. It is the first European space mission to do so.

• March 15 - John Pople, British Nobel Prize winning chemist
• July 3 - Andriyan Nikolayev, cosmonaut
• July 28 - Francis Crick, found the double helix in DNA