New Evidence Regarding Mars Magnetic Field |
| Written by spacetravel.org | |||
| Thursday, 12 May 2005 19:44 | |||
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Measurements taken by the Mars Global Surveyor satellite have shown that the huge Hellas and Argyre craters are only weakly magnetic. Scientists interpreted this to mean that Mars magnetism was already weak when meteorites struck the craters four billion years ago. They based their conclusion on the idea that if the magnetic field was weak to begin with, shock waves from large meteorite impacts could disrupt the field enough to demagnetize the rocks in the crater. Stuart Guilder of the Institute of Physics of the Earth in Paris and his colleagues studied the Vredefort meteorite impact crater in South Africa in order to verify this idea. The Vredefort crater also looks weakly magnetic from above. The team measured the strength and direction of the magnetization in rocks collected from 127 different locations inside the crater. They discovered that, despite their expectations, all of the rocks were highly magnetic, but in a jumble of different directions. They believe that the meteorite impact randomized the magnetic direction of the rocks. When one is standing on the surface, the magnetic field appears strong, but the different directions of magnetism cancel each other out from a few hundred meters above, making the crater seem demagnetized. This means that the lack of a magnetic field above Hellas and Argyre on Mars can no longer be used as proof that Mars magnetic field shut down four billion years ago. The next step will be to have robot rovers collect and analyze rock samples from these craters.
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