Dynamo Theory and its implication.
If you ever wondered on how a geomagnetic field is produced or if you have a keen interest on physics, this article is for you. This article explains Dynamo Theory, the phenomenon by which the magnetosphere of a celestial body is produced.
If you’ve ever been to the Northern Lights, you might have been awed by its beauty. Well, if you ever wondered how such a beauty is produced or how a magnetic field is produced, this article is for you. Let’s discuss about the physics under the hood which produces a magnetic field aka Magnetosphere.
Of course, it isn’t that simpler that you could jot down the answer in a single sentence, but, if it would be, the answer is “Dynamo Theory”. Although various other mechanisms for generating the geomagnetic field have been proposed, only the dynamo concept is seriously considered today. The Dynamo Theory was first was proposed by a German-born American physicist Walter M Elsasser and a British geophysicist Edward Bullard during the mid 1900s. Even though it was originally used to explain Sun’s magnetic field in its relationship with the same of earth, it was emphasized further after it was theorized by Gauss that the earth’s magnetic field has an internal origin, rather than an external origin from the Sun.
The Dynamo Theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales.
There are a few requisites for a dynamo to operate-
- An electrically conductive fluid medium.
- Kinetic Energy provided by planetary motion.
- An internal energy source to drive convective motions within fluid.
In the case of Earth, the magnetic field is induced and constantly maintained by the convection of electrically conductive liquified iron in the outer core. A requirement for the induction of field is a rotating fluid. Rotation in the outer core is supplied by the Coriolis force caused by the rotation of Earth’s inner core. It tends to organize fluid motions and electric currents into Taylor columns aligned with the rotation axis.
Despite all these requisites, tidal heating might support a dynamo too. An orbit and rotation of a planet helps provide a liquid core, and supplements kinetic energy that supports a dynamo action. Mercury has a magnetic field mainly because of tidal heating, that is what which keeps Mercury’s interior liquified. However, Saturn’s Enceladus and Jupiter’s Io too have enough tidal heating to liquify their inner cores, but they may not create a dynamo because the liquified fluid medium is not electrically conductive.
It is theorized that the Moon once had a magnetic field. Based on evidence from magnetized lunar rocks, due to its short-lived closer distance to Earth creating tidal heating, it had a magnetic field for a short span of time.
I agree that this does seem to be a mouthful to understand but, this is just a summarization of the topic. If you wish to know more about Dynamo Theory, check out on Wikipedia and Britannica.
PS.
Magnetars are a type of a neutron star which have an extremely powerful magnetic field, they are the strongest magnets in the universe. They have a very high density such that a single teaspoon of a magnetar could weigh at some billion tons. Even the strong fields of magnetars are the results from a magnetohydrodynamic dynamo process in the turbulent, extremely dense conducting fluid that exists before the neutron star settles into its equilibrium configuration.
(Wonder what happened if a Magnetar would be in our Solar System, Check out this video)