Evidence from Curiosity suggests Gale Crater once contained a lake

BBC : The two-year journey that Curiosity has taken through the Gale Crater on Mars has provided researchers with enough evidence to claim that the crater held a lake for much of its existence. A lake in Gale Crater would also explain the unusual presence of Mount Sharp at its center: Although many craters often have a central mound that forms as the ground rebounds after an asteroid or comet impact, Mount Sharp is much larger than would be expected. Curiosity has seen significant evidence of a history of flowing water in the crater as well as many different layers of sediment. And those layers have been inclined in such a way as to indicate that they were deposited as water moved down toward the center of the crater. As the water pooled there, it would have deposited the rest of the sediment it carried. After the water evaporated, wind may have eroded the softer sediments on the slopes of the crater while leaving the more heavily compacted sediment in the middle. Over time, Mount Sharp was carved out of the deposited sediments.