In 2011, planetary scientist James Wray and his colleagues reported
finding dark streaks on steep Martian slopes. The streaks appeared in warm seasons, and vanished during cold weather—evidence, they suggested, of liquid water flows. They still haven't confirmed the presence of water. But now they've found evidence
that fine-grained iron sediments seem to be carried away by some sort of flow—possibly, Wray says, the trickling of morning dew.