How might a giant asteroid impact have created Mars’s northern lowlands?

The striking hemispheric dichotomy of Mars—where the northern hemisphere is low-lying and sparsely cratered, while the southern hemisphere is high-standing and heavily cratered—is widely believed to have originated from a massive asteroid impact very early in the planet's history.1

This cataclysmic event likely created a colossal impact crater covering much of the northern hemisphere, measuring approximately 8,500 by 10,700 km (5,300 by 6,600 miles) across. Scientists estimate that the object responsible for this impact would have been more than 2,000 km (1,200 miles) in diameter. Gravity data obtained by the Mars Global Surveyor supports this theory, revealing that the Martian crust is significantly thinner under the northern plains than it is beneath the southern highlands.1