Recurring slope lineae on Mars are dark streaks that occur on steep slopes that grow and darken as spring turns to summer, gradually fading away. It has been suggested that they form by water seeping from the top of the slopes. However, not everyone accepts this interpretation. A team led by Colin Dundas of the USGS Astrogeology Center suggests that the dark streaks might be better explained by granular flows of dry sand and dust cascading down the slope. READ MORE »