Flowing Water On Mars

Mars is drier than the most arid deserts on Earth, yet scientists now know it harbors liquid water just beneath its surface. Images from the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter spacecraft reveal seeps of moisture sliding down steep Martian cliffs that come and go with the seasons. These dark streaks, called recurring slope lineae, appear on sun-facing hillsides, often inside craters. They usually advance slowly, over days or weeks, before fading away at summer’s end. Dissolved salts lower the water's freezing point, perhaps explaining why flows are seen even at low temperatures. The water doesn’t collect into streams or lakes like it might on Earth. Instead, it evaporates into the dry Martian air, leaving behind telltale traces of salt. Using instruments aboard the spacecraft, scientists detected those salts on the same cliffs where they had spied seasonal flows, confirming their aqueous nature. Watch the video to learn more.