When Alfred McEwen tells you a place on Mars has warm summers, don’t picture the Florida Keys—think Antarctica at its balmiest. McEwen, the lead scientist for the filing-cabinet-sized camera riding on NASA’s Mars Reconnaissance Orbiter, took photos five years ago of dark, water-like trails on slopes where temperatures on summer days can sometimes reach the melting point of water. But to test to see if water really created the trails, the scientists needed more than ordinary photos.

When water evaporates, it leaves salts behind, creating a chemical trail in its path. And just as each wire on a piano vibrates at a different frequency, each salt reflects a particular wavelength of light. To hunt for the salts, astronomers led by Scott Murchie of Johns Hopkins University used a smaller camera on the orbiter that’s able to capture infrared light. Analyzing the light reflected by the trails, they picked up wavelengths belonging to a variety of salts almost certainly carried by flowing water, said Murchie. The combined teams of astronomers reported their findings this September in an article in the journal Nature Geoscience.

But could life possibly exist on such a salty, freezing cold slope that’s wet only part of the year? Geologists like Joe Levy at the University of Texas in Austin seek answers to that question in Antarctica, the part of Earth most like the red planet. Levy says a whole ecosystem of small organisms enjoys the South Pole summer on occasionally damp Antarctic hillsides with Mars-like water trails. Plus, they can “just freeze dry themselves” for the off-season when it’s too cold to process food, he notes. These microbes and tiny eight-legged creatures called tardigrades can also tolerate some of the saltiest water on Earth.

But before looking for life on the water trails of Mars, we need to address more basic questions, like the source of the flowing water. It could come from underground, from precipitation, from ice melt, or salts could absorb it from the mostly dry atmosphere—but no one yet knows which. “That’s a great mystery,” says Levy.