Is there an explanation as to why Earth has a magnetic field and Venus and Mars don't?

Question

From wikipedia: http://en.wikipedia.org/wiki/Solar_system

"Earth's magnetic field protects its atmosphere from interacting with the solar wind. However, Venus and Mars do not have magnetic fields, and the solar wind causes their atmospheres to gradually bleed away into space."

Please provide a source with your answer, and don't speculate.

Answer 1

The Earth's magnetic field is nowadays pretty generally accepted to be due to circulating electric currents in the liquid part of the metal core.

Surely Mars and Venus have a metal core too, but a smaller core has less radioactivity to heat it up to melting point, and a thinner mantle lets the radioactive heat escape more quickly, so there are plausible reasons for them having a solid core and hence no magnetic field. However, I don't think any planetologists would have been surprised either way - the conditions must be pretty borderline.

Answer 2

Earth has a molten core consisting of a large percentage of
iron. As the earth rotates, the core is dragged along but at
a slower rate. It lags. For example, float a piece of wood in
a glass of water a turn the glass on a horizontal plane. Note
that the piece of wood will eventually turn in the direction of
the glass but not as fast. It lags. That means there's a relative
motion between the molten core and the rest of the planet.
This relative motion imposes an alignment of the electrostatic
forces in the iron, due to iron ions. This alignment is the
magnetic field. Mars and Venus do not have a molten core.

Answer 3

Actually, Venus does have a magnetic field, though it is much weaker than the one Earth has. But it takes more than solar wind to blow away an atmosphere. A planet's gravity plays a large part in holding the atmosphere in place. Here's a quote from Wikipedia: "An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body."

Answer 4

Funny how many people knew that Earth's magnetic field was caused by it's rotation, but completly missed the fact the Venus has almost no rotaion as the reason it has a very small field.
Mars is just small enough that's it's core is colled down and mostly solid now.

Answer 5

the earth's magnetic field comes from the dynamic nature of the liquid outer core adjacent to the solid inner core. Also the convection currents there also help produce a magnetic field. venus and mars don't have this layer so they do not have a magnetic field

Answer 6

The effect you are describing is actually what we know popularly as the Aurora Borealis and Aurora Australis, which is caused by part of the solar wind entering our atmosphere. This happens to all bodies in our solar system, and can be witnessed as the tail behind a comet, or one of the aroras. It was also part of the process when the solar system formed.

We have an amazing diversity in our solar system, no two bodies are alike and their mysteries are always revealing.

Answer 7

the inner core is solid and made of iron and rotates like the Earth this creates the magnetic field around the Earth

Answer 8

mars and venus are a solid chunk of rock

earth is solid on the outside inside different parts spin at different speeds and causes the magnetic effect

this is a simple explanation if you wish for an explanation that is more scientific with words not many people know please ask

Answer 9

I vaguely remember it having to due with the earth's rotation and the earth's core and what it is made out of. Also why true north and magnetic north aren't the same.

Answer 10

Its because of the gravity.