As it seeps down the slopes of Martian craters and mountains, it leaves narrow streaks less than five metres wide, which appear and lengthen during the warm season and fade during the Martian winter.
One possibility is that the seeps are fueled by an aquifer or melting subsurface ice.
Americans currently use 80-million pounds of pesticides a year, most of which drains into streams or seeps into the water table.
