Plasma Clouds Around the Earth

Encircling the equatorial region of the Earth, and extending to latitudes nearly as far as the Arctic Circle, are regions of space where powerful flows of particles exist. Since the late 1950s at the dawn of the Space Age, they have been called the Van Allen belts. They were at one time believed to be particles from the solar wind, trapped by the Earth's magnetic field. Like an invisible bottle, particles could enter the bottle but would have a hard time leaving.

There are actually two belts which are shaped like two nested donuts centered on the Earth. The inner belt contains 10 million-volt, high-energy protons (the stripped nuclei of hydrogen atoms), and is located between 700 kilometers and 12,000 kilometers from the Earth's surface. The outer belt contains mostly electrons with energies higher than 1 million volts, located between 25,000 and 40,000 kilometers from the Earth’s surface.

There are two other important systems of particles that invisibly orbit the Earth: the plasmasphere and the ring current. Both of these systems contain much lower energy particles than the Van Allen belts, although they occupy nearly the same regions of space extending to at least 45,000 kilometers from the Earth's surface.

Low-energy particles, with energies of a few tens of volts, surround the Earth in a vast donut-shaped cloud called the plasmasphere. The Earth's magnetic field in this region is so strong that the charged plasmasphere particles are pulled along with the Earth's 24-hour rotation. During times of severe coronal mass ejections, atoms from the Earth's atmosphere are actually pumped into the plasmasphere in a so-called polar fountain. These fountains can be detected by orbiting satellites as they pass through the arctic and antarctic regions within a few thousand kilometers of the Earth.

The ring current extends from 8,000 kilometers to nearly 30,000 kilometers from the surface and occupies nearly the same zone as the much more energetic Van Allen belts. Ring current particles carry energies of thousands of volts. It is not a complete equatorial ring, like the planet Saturn’s rings, but is only at its strongest on the night-side of the Earth. Its strength increases and decreases with the activity in the magnetotail region.

During times of severe storminess, when the solar wind magnetic polarity is south-type, the ring current becomes a powerful river of charged particles that create their own intense magnetic field. This field modifies the Earth's own field and actually decreases its intensity in the equatorial regions of the Earth. The origin of these 100,000-volt particles is something of a scientific mystery. We don't fully understand how they are energized to such high voltages within the magnetosphere.


Teacher Notes:

How do the particles that enter the Earth’s protective shield affect other Earth systems?

A system may have all three kinds of change occurring together. There are three general categories of patterns, 1) changes that are steady trends, 2) changes that occur in cycles and 3) changes that are irregular. Scientists know that what occurs on the Sun can be described as a pattern for change and that these patterns determine the interactions within the Sun-Earth connection.

• (3-5) In something that consists of many parts, the parts usually influence one another.

• (6-8) Thinking about things as systems means looking for how every part relates to others. The

output from one part of a system (which include material, energy or information) can become the input to other parts. Such feedback can serve to control what goes on in the system as a whole.

• (9-12) Understanding how things work and designing solutions to problems of almost any kind can be facilitated by systems analysis. In defining a system, it is important to specify its boundaries and subsystems, indicate its relation to other systems, and identify what its input and its output are expected to be.


Science Nuggets:

2000...IMAGE discovers a wealth of structure in the plasmasphere, and produces the first images of the ring current.

1998...Polar satellite confirms fountain of gas ejected from polar regions by disturbances in the solar wind.

1998...Geotail detects bursts of plasma in the magnetotail travelling at 2000 kilometers per second during a magnetic storm.

1990...CRRES discovers a third radiation belt located between the inner and outer Van Allen belts.