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. "The core has to have organized convection to form a dynamo," Mario Acuna of NASA's Goddard Spaceflight Center in Maryland, said. "If you disturb it with an impact, it will shut off." As the mantle cooled form the impact, there wasn't enough energy in the core to restart a dynamo from scratch, Roberts reasons, and so the magnetic field was gone forever. "Earth probably took the same kind of punishment," Roberts said. "But it's primarily a function of size. Earth has more than 10 times more heat than Mars, and much more vigorous convection." Related Links: |
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