Dry Ice or Flowing Water on Mars Surface
Recently some of the formations on the slopes of the craters on Mars were assumed to be the evidence of seasonal flowing water. However, now there is a different proposal for the formation of these structures.
According to the new proposal, the main actor might be dry ice, not flowing liquid water.
It is known that most of the seasonal icecaps and frost are formed by CO2. When sun rays penetrate to the depth of dry ice layers, it may cause sublimination (vaporising without entering a liquidation phase). This process might create a frictionless surface layer and cause the dry ice to behave like a flowing liquid carrying some deposit together with it.
So, actual reason of the formation of gullies might be flowing dry ice instead of liquid water flow.
I hope, that puzzle will be solved in a short time.