This image, a mosaic collected by the Mast Camera on the Curiosity Mars rover in December 2012, is historic. It shows what the mission science team titled “A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars” in their peer-reviewed paper published in Science a year later. Water once pooled here, for hundreds to tens of thousands of years, and where there is water, there can be life.

“We have found a habitable environment that is so benign and supportive of life that if this water had been around and you had been on the planet, you would have been able to drink it,” says John Grotzinger, project scientist on the mission (AW&ST March 18, 2013, p. 11).

Grotzinger was crowing just a little, because his mission had achieved its primary objective only four months after landing on Mars. Curiosity is not equipped to look for life, but the implications of its finding that Mars was indeed habitable are profound.

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