Earth's magnetosphere: protecting our planet from harmful cosmic energy

Earth's magnetosphere: protecting our planet from harmful cosmic energy
Earth's magnetosphere: protecting our planet from harmful cosmic energy
Anonim

NASA, yesterday published a large article about the Earth's magnetosphere, about the changes taking place in it, about the influence of solar flares on it, about the migration of the poles and about the possible change of the poles of our planet. We present you a translation of this interesting article:

Among the four rocky planets of our solar system, we can say that the "magnetic" personality of the Earth is the envy of its interplanetary neighbors.

When streams of solar matter enter the Earth's magnetosphere, they can be trapped and held in two donut-shaped belts around the planet, called the Van Allen belts. These belts cause particles to move along the lines of the Earth's magnetic field, constantly bouncing from pole to pole. This video illustrates the changes in shape and intensity of the Van Allen Belt cross section.

Unlike Mercury, Venus, and Mars, Earth is surrounded by a huge magnetic field called the magnetosphere. Created by powerful dynamic forces at the center of our world, our magnetosphere protects us from the destruction of the atmosphere by the solar wind (charged particles that the Sun constantly spews at us), the effects of radiation and particles from coronal mass ejections (massive clouds of energetic and magnetized solar plasma and radiation) and cosmic rays from deep space. Our magnetosphere acts as a protector, repelling this unwanted energy harmful to life on Earth, trapping most of it at a safe distance from the Earth's surface in two donut-shaped zones called Van Allen belts.

But Earth's magnetosphere is not a perfect defense. Oscillations in the solar wind can disrupt it, leading to "space weather" - geomagnetic storms that can penetrate our atmosphere, threatening spacecraft and astronauts, disrupting navigation systems and wreaking havoc on power grids.

The solar wind creates temporary cracks in the shield, allowing some energy to penetrate the Earth's surface every day. However, since these intrusions are short-lived, they do not cause serious problems and are accompanied by beautiful flashes of aurora (aurora).

Since the forces that generate the Earth's magnetic field are constantly changing, the field itself is also in constant motion, its strength increasing and decreasing over time. As a result, the location of the north and south magnetic poles of the Earth gradually changes, and approximately every 300,000 years - completely.

Launched in November 2013 by the European Space Agency (ESA), a constellation of three Swarm satellites provides new insights into the workings of the Earth's global magnetic field. Created by the movement of molten iron in the Earth's core, the magnetic field protects our planet from cosmic radiation and charged particles emitted by the Sun. It also provides a basis for compass navigation.

The top image, based on Swarm data, shows the average strength of the Earth's magnetic field at the surface (measured in nanoteslas) between January 1 and June 30, 2014. The second image shows the changes in this field over the same period. Although the colors in the second image are as vivid as in the first, note that the largest changes were plus or minus 100 nanotesla at a field as high as 60,000 nanotesla.

To understand what forces control the earth's magnetic field, you first need to separate the four main layers of the earth's "onion" (solid earth):

- The crust where we live is, on average, 19 miles (31 km) deep on land and about 3 miles (5 km) deep on the ocean floor.

- The mantle is a hot, viscous mixture of molten rock about 1,800 miles (2,900 kilometers) thick.

- The outer core is about 1,400 miles (2,250 kilometers) thick, composed of molten iron and nickel.

- The inner core is a solid sphere about 759 miles (1221 kilometers) thick, made of iron and nickel, about as hot as the surface of the Sun.

Internal structure of the Earth: dense solid metal core, viscous metal outer core, mantle and crust based on silicates.

Almost all of the Earth's geomagnetic field originates in the liquid outer core. Like boiling water on a stovetop, convective forces (which carry heat from one place to another, usually through air or water) constantly stir up molten metals, which also swirl in vortexes caused by the Earth's rotation. As this swirling mass of metal moves, it generates electric currents hundreds of miles wide and thousands of miles per hour as the Earth rotates. This mechanism, which is responsible for maintaining the earth's magnetic field, is known as geodynamo.

An illustration of the dynamo mechanism that creates the Earth's magnetic field: convection currents of liquid metal in the outer core of the Earth, driven by a heat flow from the inner core, organized into rolls by the Coriolis force, create circulating electric currents that generate a magnetic field.

Studying the past magnetism of the Earth is called paleomagnetism. Direct observations of the magnetic field span only a few centuries, so scientists rely on circumstantial evidence. Magnetic minerals in ancient undisturbed volcanic and sedimentary rocks, lacustrine and marine sediments, lava flows and archaeological artifacts can show the strength and direction of the magnetic field, the timing of magnetic pole reversals, and much more. By studying global evidence and data from satellites and geomagnetic observatories and analyzing the evolution of the magnetic field using computer models, scientists can plot the history of field changes over geological time.

Simple visualization of the Earth's magnetosphere at the time of the equinox.

Image

The earth is surrounded by a system of magnetic fields called the magnetosphere. The magnetosphere protects our planet from harmful solar radiation and radiation from cosmic particles, but it can change shape in response to incoming space weather from the Sun.

The mid-oceanic ridges of the Earth, where tectonic plates form, provide data for paleomagnetologists for 160 million years. As lava continually erupts from the ridges, it spreads and cools, and its iron-rich minerals align with the geomagnetic field, pointing north. When the lava cools down to about 1,300 degrees Fahrenheit (700 degrees Celsius), the strength and direction of the magnetic field at that point is “frozen” in the rock. By sampling and radiometric dating of the rock, this magnetic field record can be identified.

The study of the Earth's magnetic field has revealed much of its history

For example, we know that over the past 200 years, the magnetic field has weakened by about 9 percent on average around the world. However, paleomagnetic studies show that the field is in fact the strongest in the last 100,000 years and twice as intense as the average for a million years.

We also know that there is a well-known "weak spot" in the magnetosphere that exists all year round. Located over South America and the South Atlantic Ocean, the South Atlantic Anomaly (SAA) is the area where the solar wind penetrates closer to the Earth's surface. It arises under the joint influence of geodynamo and the tilt of the Earth's magnetic axis.While charged solar and cosmic ray particles within the SAA can fry the electronics of spacecraft, they do not affect life on the Earth's surface.

Magnetic stripes around the mid-ocean ridges show the history of the Earth's magnetic field over millions of years. The study of past terrestrial magnetism is called paleomagnetism.

We know that the position of the Earth's magnetic poles is constantly changing. Since its location was first pinpointed by Royal Navy officer and polar explorer Sir James Clark Ross in 1831, the magnetic N Pole has gradually shifted north-northwest by more than 600 miles (1,100 kilometers) and its speed forward increased from about 10 miles (16 kilometers) per year to about 34 miles (55 kilometers) per year.

The Earth's magnetic field acts as a protective shield around the planet, repelling and retaining charged particles from the Sun. But over South America and the South Atlantic Ocean, an unusually weak spot in the field - the so-called South Atlantic Anomaly, or SAA - allows these particles to sink closer to the surface than usual. SAA has no visible impact on daily surface life at this time. However, recent observations and forecasts show that the region is expanding westward and continues to weaken in intensity. The South Atlantic Anomaly is also of interest to NASA scientists who monitor changes in magnetic force in the region, both in terms of how these changes affect the Earth's atmosphere and as an indicator of what is happening to the Earth's magnetic fields deep in the globe. …

The Earth's magnetic poles are not the same as the geodesic poles with which most people are more familiar. The location of the geodetic poles of the Earth is determined by the axis of rotation around which our planet revolves. This axis does not rotate evenly like a globe on your desk. Instead, she wiggles slightly. This causes the position of the true north pole to shift slightly over time. Numerous processes on the surface of the Earth and in its interior contribute to this oscillation, but it is mainly associated with the movement of water around the Earth. Since the beginning of observations, the position of the Earth's axis of rotation has shifted towards North America by about 37 feet (12 meters), but never more than 7 inches (17 centimeters) per year. These fluctuations do not affect our daily life, but they must be taken into account in order to obtain accurate results from global navigation satellite systems, Earth observation satellites and ground-based observatories. Fluctuations can tell scientists about past climatic conditions, but they are a consequence of changes in continental reservoirs and ice sheets over time, not their cause.

Observed displacements of the North Pole between 1831 and 2007 are yellow squares. The simulated pole positions from 1590 to 2020 are circles going from blue to yellow.

Observed southerly poles in the period 1903-2000 are yellow squares. The simulated pole positions from 1590 to 2020 are circles going from blue to yellow.

The most significant changes affecting the Earth's magnetosphere are pole shifts. During a polarity reversal, the north and south magnetic poles of the Earth are reversed. While this may seem like a big problem, pole reversals are common in Earth's geological history. Paleomagnetic records, including records of variations in magnetic field strength, indicate that Earth's magnetic poles have swapped 183 times over the past 83 million years and at least several hundred times over the past 160 million years. The time intervals between reversals are highly variable, but average about 300,000 years, with the last time occurring about 780,000 years ago.Scientists do not know what determines the frequency of the pole reversal, but this may be due to convective processes in the Earth's mantle.

The position of the Earth's magnetic north pole. Poles shown are dip poles, defined as positions where the direction of the magnetic field is vertical. Red circles mark the positions of the magnetic north pole determined by direct observations; blue circles indicate positions modeled with the GUFM model (1590-1890) and the IGRF-12 model (1900-2020) in one year increments. For 1890-1900, a smooth interpolation was performed between the two models. The simulated locations after 2015 are projections.

During the pole reversal, the magnetic field weakens, but does not completely disappear. The magnetosphere, together with the Earth's atmosphere, continues to protect our planet from cosmic rays and charged solar particles, although a small amount of solid particles can fall on the Earth's surface. The magnetic field becomes erratic and multiple magnetic poles can appear at unexpected latitudes.

The earth does not always rotate around an axis through its poles. Instead, it fluctuates unevenly over time, drifting towards North America for most of the 20th century (green arrow). This direction has changed dramatically due to the change in the mass of water on Earth.

Until about 2000, the Earth's axis of rotation drifted towards Canada (green arrow, left globe). JPL scientists calculated the effect of changes in water mass in different regions (central globe) on the direction of eastward drift and acceleration of speed (right globe).

The relationship between the water mass of the continents and the oscillations of the Earth's axis of rotation in the east-west direction. Water losses from Eurasia correspond to fluctuations to the east in the general direction of the axis of rotation (top), and the Eurasian gain pushes the axis of rotation to the west (below).

No one knows exactly when the next pole reversal might occur, but scientists know they don't happen overnight. Instead, they occur over hundreds and thousands of years. Scientists have no reason to believe that a coup is inevitable.

Geomagnetic polarity over the past 169 million years, going into the Jurassic quiescent zone. Dark areas indicate periods of normal polarity, light areas indicate reversed polarity.

Supercomputer models of the Earth's magnetic field. On the left is the normal dipolar magnetic field, typical for the long years between polarity reversals. On the right is the complex magnetic field that occurs around the Earth during polarity reversal shocks.

Finally, there are "geomagnetic excursions": shorter-lived, but significant changes in the intensity of the magnetic field, lasting from several centuries to several tens of thousands of years. Tours are about 10 times more frequent than pole reversals.

The excursion can reorient the Earth's magnetic poles 45 degrees from their previous position and reduce the field strength by 20 percent. Tours are generally regional rather than global.

Three significant excursions have taken place over the past 70,000 years: the Norwegian-Greenland Sea event about 64,500 years ago, the Lashamp event between 42,000 and 41,000 years ago, and the Lake Mono event about 34,500 years ago.

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