Posted by tourdemars to Planetology at May 1, 2009 01:23 PM

Giant asteroids may have wiped out Mars's magnetic field. The energy released by massive collisions upset the heat flow in the planet's iron core that produced the magnetism, according to a new study. The finding offers a solution to the mystery of the disappearing magnetic field and sheds light on early Earth conditions. A planet's magnetic field results from a process called convection, Within the core, molten iron rises, cools, and sinks. The convection induces a magnetic field, in a system known as a dynamo. Like Earth, early Mars had a magnetic field and perhaps an atmosphere conducive to liquid water. But magnetic analysis of the martian surface indicates that when Mars was a mere 500 million years old, its magnetic field withered away. Without this shield, streams of ionizing particles spewing from the sun strip away a planet's atmosphere, killing any life that may have emerged or forcing it underground.