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Press Release: Protection at a Price from Earth's Space Storm Shield
  
System Animation (4M MPEG),12M QuickTime
 A layer in the Earth's outer atmosphere acts like a heat shield by absorbing
 energy from space storms, which reduces their ability to heat the lower
 atmosphere. However, it imposes a heavy toll for its services by creating a
 billion-degree cloud of electrified gas (plasma) that surrounds our planet.
 The plasma cloud is so ferociously hot, its particles act like radiation,
 penetrating and occasionally disrupting satellites in mid to high
 (geosynchronous) orbits. Although past space missions gave provisional
 evidence for this behavior, IMAGE provides the first global picture of the
 active role Earth's ionosphere plays in space storms, which is very
 different from the earlier view that the solar wind itself supplied the
 energetic particles responsible for these storms.
 
Atmospheric Outflow
 The Earth's space storm shield is a tenuous layer of the outer atmosphere
 (ionosphere) between 180-620 miles (300-1,000 kilometers) high that includes
 electrically charged atoms. "Just as a heat shield sacrifices itself by
 allowing its outer layers to slough off during the fiery reentry of a
 spacecraft, Earth's shield absorbs space storm energy by throwing some of
 its charged particles into space," said Dr. Stephen Fuselier of the
 Lockheed-Martin Advanced Technology Center, Palo Alto, Calif., who is lead
 author of the first of two papers on this discovery to be published in the
 Journal of Geophysical Research.
 
How is the Atmosphere Heated?
 Although the magnetosphere does a good job staving off the solar wind, Earth
 is not home free. Since the solar wind plasma is comprised of electrically
 charged particles that are moving rapidly past a magnetic field (the
 Earth's), a multimillion amp electric current is generated, which flows down
 the Earth's invisible magnetic field lines and pumps up to a trillion watts
 of power into the magnetosphere, especially above the polar regions, where
 the aurora (northern and southern lights) form. Without the space storm
 shield, heat from these enormous electric currents would cause our lower
 atmosphere (lower ionosphere) to expand and increase orbit-disrupting drag
 on spacecraft.
 
Formation of Hot Storm Plasma Clouds
 "But this protection comes with a high price, because the expelled particles
 gain tremendous speed as they leave the atmosphere, become trapped by the
 Earth's magnetic field and ultimately encircle the Earth, where they form a
 hot plasma cloud around the planet," said Dr. Donald Mitchell of the Johns
 Hopkins Applied Physics Laboratory, Laurel, Md., who is lead author of the
 second paper. Approximately half of the energy deposited by space storms in
 our atmosphere is absorbed this way, according to the researchers.
 
Sunward Flow From the Magnetic Tail
 Because of their electric charge, the expelled oxygen ions feel magnetic
 forces and are trapped within the Earth's vast magnetosphere, where they
 follow magnetic field lines like cars on a highway. Scientists know that the
 magnetosphere distorts under the impact of the solar wind, like an umbrella
 in a windstorm. In particular, the region of the magnetosphere facing away
 from the Sun (on the night side of Earth) is stretched into a long,
 tail-like shape as the solar wind blows by. Because magnetic fields have
 tension, they resist stretching and behave like rubber bands. When the
 stretching becomes too great, the night-side magnetosphere snaps back
 towards Earth, carrying the ejected ions from the ionosphere with it like an
 enormous slingshot.
 
Cold Plasma Erosion (Case A: 1.2M QuickTime), Case B: 1M MPEG
Ionospheric Effects on the Global Positioning System (40M AVI), 20M AVI
 This new view is helping scientists to better understand the effects of
 space storms. "Space storms create moving plasma clouds that interfere with
 navigation using the Global Positioning System satellites," said Dr. John
 Foster, a magnetospheric physicist with the Massachusetts Institute of
 Technology.
 
Improved Space Weather Forecasting
 Earth contributes material and the solar wind supplies the energy which
 transforms this cool atmospheric material into a dangerously hot plasma
 cloud. If it were not for the Earth's own ionosphere supplying material, the
 hot plasma cloud would be very much diminished. These new observations from
 NASA's Imager for Magnetopause to Aurora Global Exploration (IMAGE)
 spacecraft reveal that the Earth actively participates in space storms.
 
 

 

T E Moore, Head 
Interplanetary Physics Branch Code 692
NASA's Goddard Space Flight Center 
Greenbelt, MD 20771
Fax: 707-988-7835

Webmaster:  J. Rumburg