Are the dark streaks on Mars flowing water?

Drying, not wetting. The simulation showed that salts in the ground lose water precisely in the active season. That drying can weaken the grip between grains and start a dry avalanche that exposes darker material. It is a possible mechanism rather than a final ruling that there is no water.

Recurring dark streaks appear in summer on steep Martian slopes and fade afterwards. That seasonality suggests an active process, which is why they were treated as a possible sign of liquid water.

The researchers built a model of the temperature and humidity in a particular crater across the year, and tested in the laboratory what salts in the soil do under exactly those conditions.

The result is the reverse of the intuition: the salts lose water precisely in the active season. Losing the water weakens the grip between the grains, and that alone is enough to start a dry avalanche.

The surface is lightened by dust, so any exposure of the material underneath looks dark, with no wetness at all. A mark that looks like a wet flow may form precisely as the ground loses the little water it holds. This is a possible mechanism fitting one crater rather than a final ruling, and the origin of all the recurring streaks is still disputed.