Martian Cataclysm: Impact energy analysis in support of the origin of multiple anomolies on Mars (cont.)
by Gary R. Spexarth
7. Loss of Planetary Magnetic Field.
If Mars had an active dynamo at one time, than at least parts of the surface of Mars should possess remnant magnetization . Indeed, the Mars Pathfinder mission produced evidence of surface magnetization during its analysis of the Martian terrain . In addition, the latest Mars Global Surveyor data has led researchers at the NASA Jet Propulsion Lab to conclude that Mars still has a liquid iron core, similar to Earth's. 
Therefore, it is reasonable to conclude that Mars at one time likely had a functioning dynamo process, and in turn, a global magnetic field.
In order for the magnetic field to be sustained in the dynamo process, the contributions of the fluid motion that causes the field to grow must be balanced by the rate of decrease from diffusion . This ratio is on the order of the magnetic Reynolds number .
Due to the dynamic nature of the Hellas Impact, one must speculate if the sudden reduction of Mars' rotation, as well as intense pressure waves passing through the liquid core, may have disrupted the fluid flow of the liquid iron core, and thus alter the magnetic Reynolds Number to such a degree that the dynamo could no longer sustain itself.
Unless specific conditions are met, the planetary dynamo is non-regenerative . Therefore, the planetary magnetic field would remain at a depleted level, and Mars would be in the state that we find it in today.
8. Loss of Atmosphere and Surface Water
The loss of a planetary magnetic field has planetarywide implications. One of them is the loss of an entire atmosphere.
It has been estimated that at one time in its past, Mars must have had an atmospheric pressure of approximately 14.5 psi, which is the same as the current atmospheric pressure of Earth! However, without a magnetic field to protect Mars from the Sun's solar wind, its atmosphere would have been "etched" away and "blown" into space and leave it with the minimal amount of atmosphere that it has today (0.10 psi) , .
In addition, due to its small radius and low gravitational field, Mars is vulnerable to impact erosion (the process in which the shock waves and/or vapor plumes from impacts etch away portions of the atmosphere). In fact, it has been estimated that the extensive bombardment that Mars has experienced is sufficient to etch away and deplete its atmosphere from 14.5 psi to its current state of 0.10 psi. , 
With such a low atmospheric pressure, all of the surface water that is believed to once existed, including massive oceans, would have boiled away.