Possible role of brines in the darkening and flow-like features on the Martian polar dunes based on HiRISE images

► We analyzed Dark Dune Spots and flow features emanate from them. ► Gradually darkening and brightening happen between dune ripples. ► Some locations darkness appear in-situ, without feeding it from outside. ► Flow features are the darkest at their frontal end and may brighten at their source region. ► These could be explained by phase changes of brines and eutectic mixtures.