Okay, so almost all astronomical objects seem to have magnetic fields, right? Earth, stars, other planets, even neutron stars. Each has magnetic fields of varying strength, though, and varying shapes. So three questions:
What is the process that creates magnetospheres around astronomical objects, or what are their origins?
What determines the shape and orientation of magnetospheres?
What determines the strength of a magnetosphere? I can tell there is a correllation to mass, but this isn’t the whole story - Venus is roughly Earth-sized, but has a much weaker field.
The magnetic fields of the Sun and the planets that have them are caused by the dynamo effect, which depends on rotating conductive fluids. Mercury and Venus lack significant magnetic fields because their rotations are so slow, and Mars seems to lack a significant magnetic field because it lacks the necessary fluid (though why it doesn’t have the layers that Earth does, I don’t think is known). Because the magnetic fields arise from rotation, the magnetic poles of a body tend to be close to its rotational poles.
Thanks. I’m not sure I understand the dynamo effect. What about rotating conductive fluids generates the field?
Also, how does this explain neutron stars, which (I think?) don’t have conductive fluid cores, but have extreme magnetic fields?
I’m not the one to explain the dynamo effect in general. However,
The interior of a neutron star is both superconductive and superfluid: It has neither resistance nor viscosity. You actually get all sorts of interesting macro-scale quantum mechanical effects from this.
It’s a complex problem, as you’ll see at the wiki link. The dumb layman’s version, though, is that the different, rotating layers of the earth’s iron core act in similar fashion to an electric generator, in which conductors are rotated through a magnetic field … which generates electricity … which generates its OWN magnetic field.
The sun does have its own iron, but, more importantly, it’s made up of tremendous amounts of ionized gas (plasma), which is also conductive. So when the sun’s layers rotate at differing rates, you get the same effect.
As for Mars, I thought the assumption was that Mars, being smaller (more surface area:volume) than Earth and being farther from the Sun, had cooled faster than the Earth, and its core was no longer (as) liquid, and therefore not generating the same dynamo.