article_snippet.sent: Evidence of water on Mars dates back to the Mariner 9 mission, which arrived in 1971.
article_snippet.sent: Evidence of water on Mars revealed clues of water erosion in river beds and canyons as well as weather fronts and fogs.
article_snippet.sent: Viking orbiters that followed caused a revolution in our ideas about water on Mars by showing how floods broke through dams and carved deep valleys.
article_snippet.sent: Mars is currently in the middle of an ice age, so liquid water cannot exist on Mars surface at the present time.
article_snippet.sent: However, Mars seems to have been warmer and wetter in the past.
article_snippet.sent: In June 2013, Curiosity found powerful evidence that water good enough to drink once flowed on Mars.
article_snippet.sent: In September, the first scoop of soil analysed by Curiosity revealed that fine materials on the surface of Mars contain two per cent water by weight.