Why does earth have a magneic field, but venus does not?

Question

Has venus's field just decayed away, like earth's is decaying?

Answer 1

I don't think Venus is a dead planet at all. The Magellan probe provided ample evidence to suggest that Venus has at least been very active in the near geological past. It would not be a surprise if there were erupting volcanoes there now. It also has an iron core like Earth's, although I believe it doesn't have the liquid out/solid inner core that Earth has to generate its magnetic field.

One of the leading theories to explain why Venus doesn't have a magnetic field is to do with plate tectonics.

Answer 2

Mathilda is on the right track. The most logical theory to date is the Dynamo. To generate and keep a magnetic field the planet must have an armature (metallic molten core), a flux (magma) and a field (Earth crust). The difference in rotation speeds between the core and the crust some how create an electrical alignment of the metal at the core becoming a giant magnet.

Here is a challenge to my fellow astronomers/physicists, I bet, as we study other planets, that we can establish a relationship between planet size, rotation and magnetic field strength. I bet you the bigger the planet and the faster the rotation the stronger the magnetic field.

As for the core cooling down, I think that depends on the planet's size and core composition. You see, a planet like Mars (1/2 the size of Earth) don't have the mass to create enough pressure to keep the core molten. May be Earth size planets and above, have enough mass to create enough pressure to keep the core molten. Then again it all depends on what is inside.

A more recent theory postulate that during the formation of our planet, it was hit by a Mars sized planet. The collision destroyed both but when the Earth coalesced again it gained the alleged iron from the other planet. The result of this collision was the Moon. So that mean that if it wasn't by that collision the Earth might not have had a core big enough to sustain a magnetic field like we have today.

Now think about this......

What are the odds of such an event occurring to both Venus and Mars?


I'm sorry, but I don't see any where in Campbel's response saying anything about Mars.

"I don't think anybody knows for sure, but I like the "it rotates too slowly" idea as a good explanation myself."

Answer 3

Earth has a very large molten nickel and iron core, it generates an magnetic field like a big electromagnetic. As it cools down it will slowly loose it's fluidity and eventual become solid and not generate an electromagnetic field, like Mars.

The theory is that Venus is lacking an EM field because the core has either soldified, or that Venus's rotation is too slow to move the core fast enough to generate one (dynamo theory).

Answer 4

Lack of tectonic activity. That is, although it is similar composition to Earth, the nickel/iron core is not rotating enough to generate a magnetic field.
The link below gives more detail. It was "borrowed" from a previous answer to the same question a few days ago.

Answer 5

Earth's magnetic field periodically reverses, which is why it's decaying right now. It won't disappear permanently.

Earth has a large moon, which raises tides in the iron core, magnetising it. Venus has no such moon.

Answer 6

faessons wrong about the moon. the moon probably helped in giving earth the molten (mostly iron, lets not list them all) core that gives earth the magnetic fields that protect us from solar radiation.
P.S. forgot to mention the moon is constucted of debris left over when the comet hit earth but she knew that anyway

Answer 7

for some reason (personally, I blame the Moon) the Earth has a large solid iron core that is rotating inside a larger pool of molten iron that is in great flux.

Venus seems to have a molten core but no solid iron core rotation. Too bad for them. Yeah for our team!

Answer 8

Campbelp got it right. Mars core froze solid, so no dynamo to make magnetic field. Venus rotates very slowly, and that's another way to shut down the planet's dynamo effect.

Answer 9

I didn't think Venus had an iron core?

Answer 10

the obvious answer is 'venus is a dead planet'.
there are probably other more pertinant ones but the first does it for me.