Gale Crater, the site being explored by the Curiosity rover, was chosen as a landing site because its structure and composition suggested that it might preserve information about Mars’ past. And, as Curiosity’s climbed the slopes of the crater’s central peak, various discoveries have clearly indicated that Mars had a watery past.

Now, scientists have put all these individual discoveries into a big-picture view of the history of Gale Crater. And the picture shows that the crater was water-filled for hundreds of millions of years—and warm for much of that time. Plus, a separate paper indicates that, long after the crater filled up with wind-blown sand, groundwater still percolated through the area.

Reading the layers of history

The new study is built on lots of individual analyses of rock samples done by Curiosity as it headed up the slopes. Various instruments revealed the types of rocks and their chemical composition at specific locations up the slopes, building a picture of the different layers of deposits.