"Supergiant" asteroid shut down Mars' magnetic field, but "dryness" shut down Venus'

Sometimes you wish people would just get their stories straight sometime. According to this theory, Mars' magnetic field got shut down by a supergiant asteroid hitting it, probably about the size of Texas.

So why didn't something like that shut down Earth's magnetic field? Well, because you'd need an even bigger asteroid to affect the Earth. Well, isn't the leading theory of how the Moon formed, that a planetesimal the size of Mars itself hit the Earth? Wouldn't that be even bigger than a Texas sized asteroid? No answer.

Then the most ludicrous one is the explanation about Venus. So why doesn't Venus have a magnetic field? Well its mantle is too dry and stiff to allow for a dynamo effect! So why is Venus's mantle so stiff and dry? Is it because Venus's water disappeared, that's why it's so dry in its mantle? If it had a magnetic field it wouldn't have lost its water, and if it had water, it would've had a magnetic field.

Anyways, you can read about it here:

"Supergiant" Asteroid Shut Down Mars's Magnetic Field
http://news.nationalgeographic.com/news/2009/05/090511-mars-asteroid_2.html
Fri May 15 2009 16:09:31 GMT-0400 (Eastern Daylight Time)

Yousuf Khan
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