Antarctica's Don Juan Pond, the world's saltiest body of water, needs its salt to keep from freezing into oblivion. Scientists had assumed that the saltwater brine that sustains the pond must come from groundwater. But using time-lapse photography, Brown University researchers show the pond actually gets its water from snowmelt, and its salt from nearby surface sediment. The video shows pond levels increasing in daily pulses correlated with peaks in surface temperature (charted on the right), a sure signal that the water comes from melting snow. The saltwater is seen entering the pond from the west. The hydrology of a pond in one of the coldest and driest places on Earth could shed light on the potential for flowing water on Mars.