GS11: Anatomy of the Magnetosphere
So far we have discussed, how is terrestrial magnetism generated? How is the bar magnet oriented at the Earth's center? How does the solar wind affect Earth's magnetic field?
Do not forget to check the links.
Now it's time for us to hover upon the anatomy of the Earth's magnetic field. We will just hover because to understand how the magnetism is recorded in the rock, we first need to have a rough picture of the magnetic field around the Earth.
Analogous to a bar magnet, Earth too has a region around the planet. This region is known as a Magnetosphere. I believe all of us remember the fun activity which was mentioned in our elementary physics book. It described how iron nails were aligned along the field of a bar magnet. If you imagine Earth has a similar field, obviously, you will lack the number of iron nails required to trace them in space. Other planets in our solar system also have magnetospheres, but Earth has the strongest one of all the rocky planets. It is a vast, teardrop-shaped, which plays a critical role in promoting life on Earth.
Magnetic strength on the Earth's surface is 10,000 gamma.
Read ahead to find, what is gamma?
How does the magnetosphere promote life on the Earth?
Life on the Earth began around 3.8 Ga in the form of the unicellular organism. If the magnetic field was weak, even if a little bit, life would have never visited on this planet. And you were not reading this article. Also, I could not have written this article. The atmosphere- a blanket of air surrounding the Earth's surface, has several essential constituents that help in sustaining life on Earth. Be that a formation of cloud, or the air to breathe.
In the absence of Earth's magnetic field, the momentary-upset solar wind would have scrapped the air cover from around the Earth. This magnetic field shields the planet from upset solar wind and cosmic rays, as well as substantially decreases the amount of radiation that reaches the surface. The surface of the Earth or any planet would be different in the absence of the magnetosphere. The cosmic rays would have eroded the surface.
This is a major reason why Mars does not support life, whereas the Earth has one.
The side of the magnetosphere facing the Sun is compressed by the incoming solar winds and is a smaller sphere than the side away from the Sun. At daytime, the side facing the Sun has a magnetic field spread to a distance of around 6-10 times the Earth's radius (which is ~6400km), whereas the Nightside- with a magnetic tail stretches farther out to hundreds of Earth's radii, beyond the Moon's orbit.
Of all the planets, Jupiter, the largest planet, has the largest magnetic field. Its Magnetosphere is, even, BIGGER than the Sun.
Structure of the Magnetosphere:
Bow shock (1): The outermost layer of the magnetosphere, a boundary between the magnetosphere and the outer space.
Magnetosheath (2): A region between the bow shock and the magnetopause. This acts as a shock absorber that transmits the pressure from the solar wind.
Magnetopause (3): In this region, the pressure from the magnetic field is balanced with the pressure exerted by the solar wind.
Magnetotail: This is present on the opposite side of the Sun, where it extends far beyond the planet. IT has two tails- northern tail (5) and southern tail (6), pointing away.
Magnetic Cusp: Cusp means a point of intersection of two arcs. In the magnetosphere, it denotes a point where two sections or the lobes of the magnetic field meets near the pole.
Plasmasphere (7): Region away from the pole, containing low energy electrons and protons.
Measuring The Magnetic Field:
The magnetic field around the planet is measured with the help of an instrument known as a magnetometer. The strength of a magnetic field is measured in units of Tesla (SI unit) or Gauss (cgs unit).
1000 Gauss= 1 Tesla
However, the field is not as robust in strength as it sounds. The measurement of the field around a planet is done in nanotesla or, commonly called, gamma. The Earth's magnetic field varies with longitude and latitude i.e. your location on the surface.
Hidden Magnetic Portals around the Earth by ScienceCasts
The magnetic field of other planets
Image Credit: NASA, Wikipedia