BBC NEWS | Science/Nature | Mars' two-faced riddle 'solved'

BBC NEWS | Science/Nature | Mars' two-faced riddle 'solved': "The puzzle of why the northern and southern hemispheres of Mars look so different may now have been solved.

Mars' crust is thicker in the southern hemisphere, and magnetic anomalies are found in the south but not the north.

New studies in Nature magazine suggest that a massive space rock smashing into the planet could have created an abrupt disparity between the two halves.

This asteroid would have been close to the size of Earth's moon and hit Mars' northern regions, scientists say"