The magnetosphere is the region of magnetic influence of a celestial body; the nature of this region varies depending on the size of the body and the intensity of the magnetic field it generates. Most planets in the solar system have this magnetic protection layer, with the exception of Venus and Mars; icy moons are examples of bodies that lack a magnetosphere. This magnetic layer is created through electric currents flowing in space and is in a constant state of change, even flipping its orientation every few thousand years.
The Earth’s magnetosphere is defined by its internal magnetic field, solar wind plasma, and Interplanetary Magnetic Field (IMF). When this mix of free ions and electrons, from both the solar wind and the Earth’s ionosphere, become confined by magnetic and electric forces much stronger than gravity, a bullet shaped effect is created, which radiates out approximately 36,000 miles (approx. 57,936 km). Earth’s magnetosphere shields us from a wide range of the energy particles received from cosmic waves; the higher layer of the atmosphere intercepts energetic particles and circulates them throughout the magnetosphere. These trapped particles are responsible for natural phenomena, such as the aurora and natural radio emissions.
The Earth’s magnetic field almost resembles a magnetic dipole, with one pole near the North Pole and the other near the geographic South Pole. An imaginary line joining the magnetic poles would be inclined by approximately 11.3° from the planet’s axis of rotation. There is no complete understanding of how Earth’s magnetic field was formed, but its origin is believed to be associated with electrical currents produced by the coupling of convective effects and rotation in the spinning liquid metallic outer core of iron and nickel. It follows the same mechanism as what is referred to as “the dynamo effect”; the direction of Earth’s magnetic field attributed to a dynamo effect is not constantly changing.
In physics, all magnets have two poles that are distinguished by the direction of the magnetic flux. In principle these poles could be labelled in any way; for example, as “positive and negative” or “north and south”. Based on the early use of magnets in compasses they were named the “North Pole” or “North-seeking Pole” (N); and the “South Pole” or “South-seeking Pole” (S), with the North Pole pointing North; that is, the one attracted to the Earth’s North Magnetic Pole. As opposite Poles attract, the Earth’s North Magnetic Pole is, by this definition, physically a magnetic South Pole; conversely, the Earth’s South Magnetic Pole is physically a magnetic North Pole.
Inside the magnetosphere, there is the plasmasphere; a donut-shaped region containing low-energy charged particles, or plasma. This region begins at a height of 60 km, extends up to 3–4 Earth radii, and includes the ionosphere; this region rotates with Earth. There are also two concentric tire-shaped regions, known as the Van Allen radiation belts, with high-energy ions—energies 0.1–10 million electron-Volts (MeV). The inner belt is 1–2 Earth radii out, while the outer belt is at 4–7 Earth radii. The plasmasphere and Van Allen belts have partial overlap, with the extent of overlap varying greatly with solar activity.
The Earth’s magnetic field is different from the magnetic field of a bar magnet. In the case of a bar magnet, or any other type of permanent magnet, the field is created by the coordinated motions of electrons within iron atoms. However, the Earth’s magnetic field is not due to magnetized iron deposits, but mostly by electric currents in the liquid outer core; electric currents induced in the ionosphere also generate magnetic fields. Such a field is always generated near where the atmosphere is closest to the Sun, leading to daily alterations that can deflect surface magnetic fields by as much as one degree.
There is a number of scientific theories suggesting that the magnetic field is generated by Earth’s molten core, defending our planet against devastating solar winds, affects everything on Earth’s surface, from global communication to animal migration and weather patterns. There is also scientific evidence pointing out that the magnetosphere was weakened by 15% over the past 200 years, and this, according to scientists’ claims, could be a sign that the Earth’s Poles are about to flip! Over the years, scientists noticed that the Earth has flipped its polarity many times; yet, there is no indication that the Earth’s magnetic field has ever disappeared.
References
nasa-usa.de
tokenrock.com
solarphysics.livingreviews.org
This article was first published in print in SCIplanet, Spring 2017 issue.