EARTH'S MAGNETOSPHERE: CHARACTERISTICS, STRUCTURE, GASES - PHYSICAL - 2024

The magnetosphere of the Earth is the magnetic envelope of the planet against the current of charged particles that the Sun emits continuously. It is caused by the interaction between its own magnetic field and the solar wind.

It is not a unique property of the Earth, since there are many other planets in the solar system that have their own magnetic field such as: Jupiter, Mercury, Neptune, Saturn or Uranus.

Figure 1. The Earth's magnetosphere and its interaction with the solar wind. Source: Wikimedia Commons.

This stream of matter that flows from the outer layers of our star, does so in the form of rarefied matter, called plasma. This is considered the fourth state of matter, similar to the gaseous state, but in which high temperatures have provided an electric charge to the particles. It consists mainly of protons and free electrons.

The solar corona emits these particles with so much energy that they can escape gravity, in a continuous flow. It is the so-called solar wind, which has its own magnetic field. Its influence extends throughout the Solar System.

Thanks to the interaction between the solar wind and the geomagnetic field, a transition zone is formed that encloses the Earth's magnetosphere.

The solar wind, which has a high electrical conductivity, is responsible for distorting the Earth's magnetic field, and compresses it on the side facing the Sun. This side is called the day side. On the opposite side, or night side, the field moves away from the Sun and its lines stretch out, forming a kind of tail.

characteristics

- The areas of magnetic influence

The solar wind modifies the Earth's magnetic field lines. If not for him, the lines would be expanded to infinity, as if it were a bar magnet. The interaction between the solar wind and the Earth's magnetic field gives rise to three regions:

1) Interplanetary zone, where the influence of the Earth's magnetic field is not perceptible.

2) Magnetofunda or magnetoenvelope, being the area where the interaction between the terrestrial field and the solar wind occurs.

3) Magnetosphere, is the region of space that contains the Earth's magnetic field.

The magneto cover is limited by two very important surfaces: the magnetopause and the shock front.

Figure 2. Structure of the magnetosphere. Source: Wikimedia Commons.

The magnetopause is the boundary surface of the magnetosphere, approximately 10 Earth radii on the day side, but it can be further compressed, especially when large amounts of mass are shed from the solar corona.

For its part, the shock front or shock arc is the surface that separates the magneto sheath from the interplanetary zone. It is at this edge where the magnetic pressure begins to slow down the solar wind particles.

- The interior of the magnetosphere

In the diagram in figure 2, in the magnetosphere or cavity that contains the Earth's magnetic field, well-differentiated areas are distinguished:

- Plasmasphere

- Plasma sheet

- Magneto glue or magnetic glue

- Neutral point

Plasma sphere

The plasmasphere is an area formed by a plasma of particles from the ionosphere. Particles coming directly from the solar corona that have managed to sneak in will also stop there.

All of them form a plasma that is not as energetic as that of the solar wind.

This region begins 60 km above the earth's surface and extends up to 3 or 4 times the earth's radius, including the ionosphere. The plasmasphere rotates alongside the Earth and partially overlaps with the famous Van Allen radiation belts.

Magneto glue and plasma sheet

The change in the direction of the terrestrial field due to the solar wind, originates the magnetotail, and also a confined zone between magnetic field lines with opposite directions: the plasma sheet, also known as the current sheet, of several terrestrial radii thick.

Neutral point

Finally the neutral point is a place where the intensity of the magnetic force is completely canceled. One of them is shown in figure 2, but there are more.

Between the day and night part of the magnetopause there is a discontinuity, called the cusp, where the lines of magnetic force converge towards the poles.

It is the cause of the northern lights, since the particles of the solar wind rotate in a spiral following the magnetic lines. Thus they manage to reach the upper atmosphere of the poles, ionizing the air and forming plasmas that emit brightly colored light and X-rays.

Gases

The magnetosphere contains appreciable amounts of plasma: a low-density ionized gas made up of positive ions and negative electrons, in proportions such that the whole is almost neutral.

The density of plasma is highly variable, ranging from 1 to 4000 particles per cubic centimeter, depending on the area.

The gases that originate the plasma of the magnetosphere come from two sources: the solar wind and the terrestrial ionosphere. These gases form a plasma in the magnetosphere made up of:

- Electrons

- Protons and 4% of

- Alpha particles (helium ions)

Complex electric currents are created inside these gases. The plasma current intensity in the magnetosphere is approximately 2 x 10 ²⁶ ions per second.

In the same way, it is a highly dynamic structure. For example, within the plasmasphere, the half-life of plasma is several days and its motion is primarily rotational.

In contrast, in more external regions of the plasma sheet, the half-life is hours and its movement is dependent on the solar wind.

The gases of the solar wind

The solar wind comes from the solar corona, the outer layer of our star, which is at a temperature of a few million Kelvin. Jets of ions and electrons shoot out from there and scatter through space at the rate of 10 ⁹ kg / s or 10 ³⁶ particles per second.

The very hot gases that come from the solar wind are recognized by their content of hydrogen and helium ions. One part manages to enter the magnetosphere through the magnetopause, through a phenomenon called magnetic reconnection.

The solar wind constitutes a source of matter loss and angular momentum of the Sun, which is part of its evolution as a star.

Gases from the ionosphere

The main source of plasma in the magnetosphere is the ionosphere. There the predominant gases are oxygen and hydrogen that come from the earth's atmosphere.

In the ionosphere they undergo an ionization process due to ultraviolet radiation and other high-energy radiation, mostly from the Sun.

The plasma of the ionosphere is colder than that of the solar wind, however a small fraction of its fast particles is capable of overcoming gravity and the magnetic field, as well as entering the magnetosphere.

References

1. ILCE Digital Library. The Sun and The Earth. A stormy relationship. Recovered from: Bibliotecadigital.ilce.edu.mx.
2. POT. The tail of the magnetosphere. Recovered from: spof.gsfc.nasa.gov.
3. POT. The magnetopause. Retrieved from: spof.gsfc.nasa.gov.
4. Oster, L. 1984. Modern Astronomy. Editorial Reverté.
5. Wikipedia. Magnetosphere. Recovered from: en.wikipedia.org.
6. Wikipedia. Solar wind. Recovered from: es.wikipedia.org.