"Once it impacted, there were no tidal forces anymore so it couldn't power the dynamo," Arkani-Hamed told Discovery News. The theory could explain why Mars' vigorous core suddenly grew still. "Maybe a core dynamo wasn't powered by convection, but by asteroid tidal forces," he said. Walter Kiefer with the Lunar & Planetary Institute in Houston follows the logic, but doesn't see how an asteroid as large as the one needed to tug Mars' core would have been captured by the planet's gravity in the first place. "I just don't know how to dissipate the energy to get it into orbit around Mars, " he said. "Until that step is made, it's hard for me to regard this as the right model." The loss of Mars' magnetic field may have played a critical role in the planet's evolution from the warm and wet world scientists suspect it was into the cold, dry desert that exists today. Magnetic fields, similar to Earth's, protect planets from cosmic rays. They also help maintain the atmosphere by shielding molecules from solar radiation. Related Links: |
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