Liquid water might not be a distant memory on Mars. New data suggest that water flows on the Red Planet even today. Seasonal dark streaks etched onto some slopes are coated with salts that need liquid water to form, researchers report online September 28 in Nature Geoscience. The Mars Reconnaissance Orbiter recorded spectra showing hydrated salts at four locations on Mars.
The salty trails appear annually, only in warmer seasons. Rising temperatures probably drive water to the surface, though whether the source is buried ice, local aquifers or something else is unclear. The salt may help keep the water liquid by lowering its freezing point, the researchers say.