Did an Asteroid Kill Mars' Magnetic Field?

One of the last giant meteors blew a hole 1,864 miles wide in the planet, creating Utopia basin in the planet's northern hemisphere. At about 4.1 billion years old, Utopia is the oldest crust on the planet that doesn't show signs of magnetism, meaning the rocks must have cooled at a time when there was no magnetic field.

Roberts and a team of researchers calculate that the Utopia impact could have done in the magnetic dynamo, which was already flagging as the planet cooled. It injected approximately one trillion megatons of energy into the Martian mantle, or close to 10 trillion times the explosive energy of the nuclear bomb used at Hiroshima.

The heat spread in an instant as a supersonic shockwave rippled through the planet. Then, over the next 30 million years, the overheated mantle acted as a blanket for the core, preventing it from circulating enough to maintain a magnetic field.

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