Division of Plasma Physics

Plasma in Space

The sun and its environment give a sample of the cauldron of activity such processes introduce. Deep beneath the solar surface, dynamo effects generate tubes of magnetic flux that can bob up and form great arches that become visible as striations of plasma in the solar atmosphere. The "footpoints" where the flux tubes emerge from the surface often coincide with the relatively cool areas called sunspots. By poorly understood processes, generally referred to with the catch-all phrase "plasma instabilities," these arches, often carrying tremendous blobs of plasma with them, can suddenly erupt, hurling the plasma and the fields threading it out into space. Or magnetic interactions can violently heat a smaller volume of plasma, which then spits out fast particles and energetic radiation.

If any of this solar shrapnel strikes the magnetic field that shrouds the Earth-a plasma-filled structure called the magnetosphere-the result can be geomagnetic storms that can destroy delicate satellite equipment and knock out power grids on the ground. On a more cheerful note, when the charged particles generated from these processes speed along field lines where they plunge into the Earth at the magnetic poles, the particles crash into nitrogen and oxygen atoms in the upper atmosphere and produce the beautiful aurorae or Northern and Southern Lights. All of these phenomena take place in response to the continual outward gusts of particles from the sun, called the solar wind. In general, predicting the vagaries and vicissitudes of this "space weather" is a major motivation for studying plasmas in the solar system.

Moving farther out into space, one finds that fascinating plasma phenomena continue to proliferate: The pressure of interstellar plasmas and fields contains the solar wind inside an irregularly shaped region called the heliosphere. Extending for several hundred light years around the heliosphere is a mysterious "bubble" of hot, x-ray-emitting plasma, a structure that may have been caused by a nearby supernova explosion in the distant past. Deeper into the Milky Way, understanding the intense radiation from spinning neutron stars called x-ray pulsars involves plasma physics in one of its most extreme settings. Thought to consist of a kind of infernal version of Earth's aurorae, the displays probably come about as material ripped from a binary stellar companion falls down the neutron star's field lines. The magnetic field strength can be so large and the spiraling orbits of electrons so tight that, like electrons in an atom, their motion becomes quantized, totally altering the character of the plasma.

figure 14

TURBULENT, WEED-LIKE magnetic structures emerging from the solar surface, as observed by the Soft X-ray Telescope experiment on the Yohkoh solar research spacecraft of the Japanese Institute of Space and Astronautical Science (ISAS). [The x-ray telescope was prepared by the Lockheed Palo Alto Research Laboratory, the National Astronomical Observatory of Japan, and the University of Tokyo with the support of NASA and ISAS]

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figure 15b

AURORAE observed (a) from the space shuttle [Courtesy of NASA] and (b) from Earth [Courtesy of David Fritts, University of Colorado].

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