NASA'S Mars rover Opportunity has discovered evidence of water on the planet. Indeed, Opportunity was able to find enough evidence of nonacidic drinkable water that researchers believed Mars may have at one point had favorable conditions to sustain life.
The rover has been investigating Mars for a decade and is a part of the Mars Exploration Rover Mission launched in 2003. The second rover involved in that mission, Spirit, ceased being operational in 2010 after getting stuck in soft soil on Mars.
Opportunity was investigating "Cape York" when researchers discovered a cracked rock they believed had evidence of water. The features of the rock, called "Esperance," had been changed by running water, and the researchers believe there was more than just trace amounts of evidence due to the erosion as well as the rock's composition, NASA said in a statement.