region in the atmosphere where magnetic phenomena and the high atmospheric conductivity caused by ionization are important in determining the behaviour of charged particles.
The Earth, in contrast to Mars and Venus, has a significant surface magnetic field (approximately 0.5 gauss), which, like its gravitational field, becomes weaker as the distance from the centre of the Earth increases. In the direction of the Sun, at approximately 10 Earth radii (almost 65,000 km, or 40,000 miles), the magnetic field is so weak that the pressure associated with particles escaping from the Earth’s gravity is comparable to the opposing pressure associated with the solar wind—the flux mainly of protons and electrons escaping from the Sun’s gravitational field. This equilibrium region, with a characteristic thickness of 100 km (60 miles), is called the magnetopause and marks the outer boundary of the magnetosphere. The lower boundary of the magnetosphere is several hundred kilometres above the Earth’s surface.
On the night side, or the side away from the Sun, the forces associated with the magnetic field and the solar wind are parallel, and thus the magnetosphere extends a considerable distance, possibly even several astronomical units (one astronomical unit is the average distance between the Earth and the Sun, about 1.5 × 108 km).
In the direction perpendicular to the solar wind, the random motion of the solar-wind particles exerts a small pressure on the magnetic field, constricting the magnetosphere slightly. The net result is that the shape of the magnetosphere in gross terms is similar to that of a comet, with the Earth located near the nucleus, or head, of the “comet” and the magnetospheric “tail” trailing out well beyond the Earth, away from the Sun.
Between 10 and 13 Earth radii toward the Sun, there exists the magnetosheath, a region of magnetic turbulence in which both the magnitude and direction of Earth’s magnetic field vary erratically. This disturbed region is thought to be caused by the production of magnetohydrodynamic shock waves, which in turn are caused by high-velocity solar-wind particles. Ahead of this bow shock boundary, toward the Sun, is the undisturbed solar wind.
The-Van-Allen-radiation-belts-contained-within-Earths-magnetosphereThe Van Allen radiation belts contained within Earth’s magnetosphere. Pressure from the solar wind …[Credits : Encyclopædia Britannica, Inc.]
A-perspective-view-of-the-northern-portion-of-the-magnetopauseA perspective view of the northern portion of the magnetopause current, as seen from above the …
Link to this article and share the full text with the readers of your Web site or blog-post.
If you think a reference to this article on "magnetosphere" will enhance your Web site,
blog-post, or any other web-content, then feel free to link to this article,
and your readers will gain full access to the full article, even if they do not subscribe to our service.
You may want to use the HTML code fragment provided below.
We welcome your comments. Any revisions or updates suggested for this article will be reviewed by our editorial staff. Contact us here.
Regular users of Britannica may notice that this comments feature is less robust than in the past. This is only temporary, while we make the transition to a dramatically new and richer site. The functionality of the system will be restored soon.