|Missing Magnetic Field|
But that may just be part of the story.
A team of researchers led by Jafar Arkani-Hamed of the University of Toronto in Canada believe a large asteroid circling the planet set up a gravitational tug-of-war that got Mars' core churning. Eventually, the asteroid lost its grip and crashed into its parent planet. Mars paid a dear price as well. Without the tidal forces, the planet's core lost its momentum, killing off the magnetic field.
What remain are patches of strong magnetic imprints in the oldest parts of Mars' crust. Because the fresher surface features are magnetic-free, scientists believe Mars lost its shield about four billion years ago.