How heavy rainfalls shaped Mars surface in the distant past

It is now established fact, that dry, cold and lifeless Mars, 3 billion years ago was wet planet with thick atmosphere and rich hydrosphere. In new study, published in Icarus, the team  from the Smithsonian Institution and the Johns Hopkins University Applied Physics Laboratory show that changes in the atmosphere on Mars made it rain harder and harder, which had a similar effect on the planet's surface as we see on Earth.

Image: Elsevier -  Valley networks on Mars show evidence for surface runoff driven by rainfall 

The study explains how the geologic processes associated with the modification of martian impact craters, which occurred throughout the Noachian  period ( from 4 to 3 billion year ago) could be a result of the changing nature of rainfall as the primordial atmospheric pressure on Mars waned through time. In the beginning of the Noachian, the atmospheric pressure on the Mars' surface was about 4 bars (4 times higher than on Earth's sea level). Due to its low mass and number of other factors (one of them mays be solar wind and the absence of magnetic field), Mars continued to loose its atmosphere and to the end of Noachian the pressure was 1.5 bar.   At pressures between ∼3.0 and 4.0 bars, sediment transport from rain splash could occur, but surface runoff would have been limited, which could explain the modification of impact craters. When atmospheric pressures dropped to ∼1.5 bars, rainfall intensity could begin to exceed the infiltration capacity of most soils, which would be necessary to initiate martian valley network formation. This is the timepoint, where Great Canyon Vallis Marineris could form.

This is the first study, taking into account atmospheric changes as well as martian gravity, which is 1/3 of Earth's.

The full article: http://www.sciencedirect.com/science/article/pii/S0019103516306005