CAN you flip a planet鈥檚 magnetic field on and off like a light switch? An asteroid could have done just that to Mars 4 billion years ago.
Mars once had a magnetic field, which may have been driven by a dynamo formed from the convection of material in the core, much like the Earth鈥檚 is today. Yet crater records suggest the Martian dynamo died quickly, over a few tens of thousands of years, something researchers struggle to explain.
Now Jafar Arkani-Hamed of the University of Toronto, Canada, and colleagues say the gravitational tug of an orbiting asteroid may have powered a dynamo by pulling on the fluid in Mars鈥檚 core. The team鈥檚 lab and model simulations showed that an asteroid orbiting 75,000 kilometres above Mars could have maintained a dynamo for 400 million years, before the rock crashed into the planet and switched it off (Journal of Geophysical Research, ).
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Some researchers are sceptical. While an asteroid might have had enough energy to churn fluid in the planet鈥檚 core, much more energy is needed to set up the dynamo to begin with, according to David Stevenson of the California Institute of Technology in Pasadena. 鈥淚t would be like looking at a boulder on top of a hill without asking what it took to get it there,鈥� he says.
