Martian Cataclysm: Impact energy analysis in support of the origin of multiple anomolies on Mars (cont.)
by Gary R. Spexarth
9. Massive Cratering in the Southern Hemisphere.
The previous sections dealt only with the Hellas crater. But what if the entire Southern Hemisphere experienced massive bombardment in a relatively short period of time?
93% of craters greater than 30 km lie in the southern hemisphere ! Why is it that most of the craters lie in the Southern Hemisphere? Current theory suggests mantel convection as the cause . In other words, it is believed that there used to be about the same density of craters in the North, just as in the South, but the mantel overturned due to convection and the craters were lost forever.
Figure-10: This image, taken in early September 2000 by the Mars Global Surveyor's Mars Orbiter Camera, shows a group of sand dunes at the edge of a much larger field of dark-toned dunes in Proctor Crater. Such sand formations erosion patterns would make it difficult to distinguish between the ages of craters based only on the "sharpness" of their rim features.
However, an alternate option must be considered as well.
Recently, it has been proposed that the Southern Hemisphere was bombarded in a relatively short period of time due to an object that broke up prior to impact . It is interesting to note that the two moons of Mars are not spherical, but rather potato shaped. Are they remnants of the object that broke up and impacted the Southern Hemisphere?
Also, the boundary of the Southern Craters forms a great circle (a circle with a circumference that is equal to the distance around the equator). In other words, if Mars were a wet beach ball and a handful of sand was thrown at it, the sand would stick on only one side of Mars. The boundary of the sand would form a great circle. In fact, the boundary of the Southern Craters form a great circle! This can partially be seen in Figure- 1.
In addition, Mars has over 170 elliptical craters greater than 3 km (compared to only 4 or 5 on the Moon). Elliptical craters are formed when an impact occurs at a shallow angle.  Shallow angle impacts would be expected if the Southern Hemisphere was bombarded during one massive "blast" of impacts. In fact, many of the elliptical craters are orientated along great circles. 
Critics argue that the Southern Hemisphere could not have been bombarded at the same time because some of the crater rims are sharp, while others are eroded. It is thought that this is a clear sign that the impacts occurred at vastly different times, since the older craters would have more of an eroded rim than newly formed craters.
However, shouldn't different rim patterns be expected on a planet that has dust storms, even if the craters are the same age? The Mars dust storms would surely form all kinds of different erosion formations along crater rims over thousands of years, independent of their true age. In fact, recent Mars photos have shown various erosion patterns and "sand dunes" due to the Mars winds as shown in Figure-10. This type of surface process could conceal the actual age of the craters.
The age of planet surfaces are estimated based on the number of craters that are counted. In other words, the surfaces with the more craters are older. By counting craters on the moon and measuring the amount of solar radiation in the craters during the Apollo missions, the age of the lunar surface was estimated. By assuming that projectiles impacted Mars with the same frequency that they hit the moon, it has been estimated that the surface of Mars is over 3 billion years old .
But, what if it isn't 3 billion years old? What if the impacts did not occur slowly throughout the life of the planet, but rather, they occurred suddenly, in a short amount of time, and the surface erosion is masking their true age to us distant observers? Then we have no way of dating the surface without actually going there and investigating. We may find that the current surface of Mars may only be thousands of years old instead of billions! Maybe in the near past it still had running water and an atmosphere! The implications of such are astounding!