tallsteve

Watching The Planets on the freeview box, all about the sun. It was talking about the solar wind and how the Earth's magnetic field protects us from the wind, and into the bargain produces the Aurora.

Thing is, why is the Earth's magnetic field strong enough to deflect the wind, but a planet of roughly equal mass (Venus) not able to?

Current theory suggests that the outer core of the Earth produces the magnetic field, and therefore a geologically active body should produce a strong field (the moon is inactive, therefore no magnetic field) - and as far as I understand it, Venus is the most geologically active planet (at least in terms of volcanic activity).

Any science bods out there with an answer, or at least a few theories!?

TopBanana

I've read that although Venus was once very active, the core has probably now solidified.

DaveD

iTrader: (2)

Is it anything to do with the centre of the Earth being made out of iron??

Iron's quite good for making magnets......

warrenm2

^^ wot he said

OllyK

As mentioned the Earth has a mantle of molten iron which produces the magnetic field. Other planets may well be active, but not necessarily have the mass of iron that Earth has.

TopBanana

Venus definately has iron in the middle of it just like us

DaveD

iTrader: (2)

"One puzzling fact is that Venus, unlike the Earth, has no magnetic field. (When exploring Venus, you can throw your compass away. It won't work). It's not certain why Venus has no magnetic field. The magnetic field of the Earth is caused by convection currents in the liquid outer core. Perhaps the metallic core of Venus is entirely solid; or perhaps the slow rotation of Venus is responsible for the lack of currents in its core. "

Because of its slow rotation (243 days) and its predicted lack of internal thermal convection, any liquid metallic portion of its core could not be rotating or convecting fast enough to generate a measurable planetary magnetic field. Limits on magnetic field strength from the Magellan magnetometer data shows that the Venus magnetic field is a miniscule 0.000015 times Earth's field.
...left-over heat energy from the formation of the planet was probably high enough to drive circulating currents and convection leading to a strong 'dynamo' magnetic field. After this heat was fully dissipated by leaking out through the planets surface, the currents ceased to flow vigorously and the magnetic field decayed to its present level. "

Seems it's the molten iron that drives the magnetic field.

tallsteve

Excellent stuff!

I found out that the solid core of earth doesn't act as a giant bar magnet as the internal temp (something in the region of 1043K) scatters the magnetic effects, and that indeed it is the convection currents in the molten outer core that generates the field.

Seems that a combination of rotation of the planet and a molten outer core could well be the answer.

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