Friday, January 21, 2011

Multiple Asteroid Strikes May Have Killed Mars’s Magnetic Field

Once upon a time, Mars had a magnetic field, just like Earth. Four billion years ago, it vanished, taking with it the planet’s chances of evolving life as we know it. Now scientists have proposed a new explanation for its disappearance.
A model of asteroids striking the red planet suggests that, while no single impact would have short-circuited the dynamo that powered its magnetism, a quick succession of 20 asteroid strikes could have done the job.
“Each one crippled a little bit,” said geophysicist Jafar Arkani-Hamed of the University of Toronto, author of the new study. “We believe those were enough to cripple, cripple, cripple, cripple until it killed all of the dynamo forever.”
Rocky planets like Earth, Mars, Mercury and even the moon get their magnetic fields from the movement of molten iron inside their cores, a process called convection. Packets of molten iron rise, cool and sink within the core, and generate an electric current. The planet’s spinning turns that current into a magnetic field in a system known as a dynamo.
Magnetic fields can shield a planet from the constant rain of high-energy particles carried in the solar wind by deflecting charged particles away from the surface. Some studies have suggested that Earth’s magnetic field could have protected early life forms from the sun’s most harmful radiation, allowing more complex life to develop. But traces of magnetism in the Martian surface reveal that the red planet lost its magnetic field some four billion years ago, leaving its atmosphere to be dessicated by the harsh solar wind.

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