How the Red Planet got two faces

 作者:杭佩拇     |      日期:2017-12-08 01:01:33
A GIANT asteroid that struck Mars a glancing blow could explain why the planet is lop-sided. Mars’s northern hemisphere is much flatter and more low-lying than the southern hemisphere. The difference in average elevation between the two is about 5 kilometres. One theory from the 1980s was that a giant asteroid about 300 kilometres across had hit the planet sometime in its early history, causing a permanent depression in the northern hemisphere. Now, computer simulations by a team led by Margarita Marinova of the California Institute of Technology in Pasadena confirm that a giant asteroid could have done the job,