NASA’s Curiosity rover touched down on Mars in August 2012, and it’s been cruising around, shooting lasers at rocks, drilling into the ground, and performing science experiments ever since. Just last week, news came out that Curiosity had found something salty. The rover is driving across Gale Crater, an ancient Martian lake bed that was once filled with water, and has discovered sulfate salts.

Scientists think this is likely due to a very dry period when water evaporated, leaving the salts behind. Our own Earth stays wet because we have an atmosphere and a magnetic field, which keeps our planet watery and healthy so we can comfortably survive. But the story for Mars is a bit more complex. Billions of years ago, Mars had an atmosphere but it’s always had a rather small magnetic field, so the solar winds from the Sun stripped the atmosphere away over time—leaving it the dry, arid planet we have grown to love.

This week we’re going to rove around on Mars alongside the biggest, baddest, robot on the red planet.

NASA tends to name the rocks that Curiosity finds along its journey. Now meet “Old Soaker.” This slab is 3 feet long and has definitely seen some things over the past 3.5 billion years. The crackling effect is due to puddles pooling over this rock and drying out, and pooling again and drying out—a process that repeated itself for aeons, leaving behind this textured look.Photograph: NASA/JPL-Caltech/MSSS
This group of rocks is called Squid Cove, and like Old Soaker, it has seen a lot of wet and dry spells. Most of what has created these formations is sediment building up over billions of years, and Martian geologists seek to infer the water evaporation cycle from the patterns and materials they see. Photograph: NASA/JPL-Caltech/MSSS
The Mars Reconnaissance Orbiter is a workhorse satellite that has taken some of the most stunning photos of Mars ever. These rolling blue hills and dunes are the floor of Gale Crater. In these HiRise camera images, the blue represents the type of material on the ground, which in this case would be extremely fine sand. These false colors are created by the HiRise camera processing—black might indicate salty water, for example.Photograph: NASA/JPL-Caltech/University of Arizona