"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 he

"Supergiant" Asteroid Shut Down Mars's Magnetic Field
http://news.nationalgeographic.com/n...steroid_2.html
Fri May 15 2009 16:09:31 GMT-0400 (Eastern Daylight Time)

Yousuf Khan