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![]() Right: If a camera didn't compensate for the bright sunlight in space, stars would be seen in the background and the Earth would appear as a bright white orb. Because distant stars aren't as bright as the Earth, a low photo exposure results in a black background. The magnetosphere provides a barrier between our planet and particles continually given off by the Sun's corona called the "solar wind." These particles constitute a plasma - a mixture of electrons (negatively charged) and ions (atoms that have lost electrons, resulting in a positive electric charge). |
"99.9 percent of the Universe is made up of plasma," says Dr. Dennis Gallagher, a plasma physicist at NASA's Marshall Space Flight Center. "Very little material in space is made of rock like the Earth."
Gallagher has developed a general model to describe the density
of the plasma surrounding the Earth. His paper, "Global
Core Plasma Model," will be published in the Journal
of Geophysical Research. "Core plasma" refers to
the low-energy plasma (zero to 100 electron volts) that makes
up the plasmasphere. Right: Click the image for a 3D simulation of the magnetosphere's shape. The Sun is off screen to the left. The animation begins showing the Earth, which recedes as the shape and size of the magnetosphere comes into view. The solar wind deforms the magnetosphere into its characteristic shape. Where the magnetosphere and the solar wind meet is the "bow shock," represented in the animation by a faint, translucent bullet shape. Credit: Digital Radiance |
"We've been flying in plasma for over 40 years and have
slowly gained a statistical picture of what things are like,
such as the density and proportion of oxygen, hydrogen, and helium,"
says Gallagher. |
From the equator to the middle latitudes of Earth, the ionosphere joins smoothly with the plasmasphere. Beyond the outer boundary of the plasmasphere, the densities of plasma in the magnetosphere can fall as low as 0.01 particles/cm3. "The plasma environment around the Earth is a natural
extension of Earth's atmosphere, ionized by the Sun," says
Gallagher. "Any planet that has an atmosphere is going to
have energy from the Sun imparted to the atoms. The consequences
are that lighter elements escape. But Earth's magnetic field
traps much of this escaping gas. A planet like Mars that has,
at best, a weak magnetic field, also has a very thin atmosphere.
Some researchers have speculated that the Earth's magnetic field
may pla Gallagher's model may contribute to our understanding of how the Earth's plasma affects our quality of life. Radio waves and power lines are affected by the presence of plasma, as are satellites and the Space Shuttle. Plasma can cause an electric charge to accumulate on one part of a spacecraft but not another, sometimes resulting in an electric arc, or discharge. These electric arcs can disrupt or destroy sensitive electronic components. Gallagher will be able to refine his model with data from the IMAGE satellite, due to launch in February 2000. IMAGE will give us a better picture of the Earth's magnetosphere, and because plasma is bound to magnetic fields, IMAGE should also improve our understanding of how the plasmasphere and the magnetosphere interact. |
Space
Weather Camera Set for Launch in 2000 - Feb. 16, 1999 NASA's Office of Space Science press releases and other news related to NASA and astrophysics |
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