The Mars Exploration Rover "Spirit" safely lands on the Red Planet | January 3, 2004 | HISTORY

The Mars Exploration Rover Spirit lands on the Red Planet on January 3, 2004. 21 days later, its twin, Opportunity, also arrived safely. In one of the longest and most successful missions in NASA history, Spirit would survey Martian geography for the next seven years, while Opportunity remained active until June of 2018.

The rovers' primary mission was expected to last 90 sols, the term used for Martian days. In March, scientists announced that they had made a momentous discovery: a survey of Martian rocks strongly suggested that water had once flowed there, and analysis of Opportunity's landing site indicated that it had once been the bed of a salty sea. Later in 2004, Opportunity also discovered the first meteorite to be found on Mars.