Scientists Plan Fall Colors for Sky

EARTH scientists, literally, are preparing to paint the sky. The two-ton satellite that a commercial Atlas rocket launched July 25 for the United States Air Force and National Aeronautics and Space Administration (NASA) carries 24 canisters packed with barium, calcium, lithium, and strontium. Experimenters hope to release those chemical crayons in a series of tests between September and next July. They want to color in some of the invisible phenomena in the magnetosphere - the space around Earth controlled by this planet's magnetic field.

Glowing fluorescently under solar radiation, electrically charged atoms of these chemicals will spread out along the lines of magnetic force. They will help scientists trace the forces involved in magnetic storms and auroras. Scientists have, for many years, conducted simple one-shot experiments of this kind using chemicals released by rockets. But this is the first time they have had equipment on site in space to carry out complex experiments over a long period of time.

``We're using space as a laboratory for fundamental research,'' says experimenter Morrie Pongratz of the Los Alamos (New Mexico) National Laboratory. ``Instead of engaging in long periods of observation of naturally occurring phenomena, we're setting up artificial situations, creating disturbances, and watching what happens.''

In one such experiment, for example, Dr. Pongratz's Los Alamos colleague, David Simons, hopes to study the behavior of a type of disturbance, called a magnetic substorm, in which electrons fall into the atmosphere to cause auroras. He plans to dump barium from two of the canisters when a storm seems imminent. He hopes this will trigger the storm. Then cameras on the ground and on Air Force planes plus the satellite's own instruments can track its development.

There is more to this satellite than painting the magnetosphere. Called the Combined Release and Radiation Effects Satellite (CRRES), it measures the strength and concentration of electric fields and various kinds of particles as well as magnetic forces. CRRES also carries electronic materials to test their ability to survive radiation in space.

However, the main purpose of the $189 million satellite is to explore the magnetosphere. Here matter exists in the state physicists call plasma. It is a mix of positively charged particles called ions and negatively charged electrons. The positive and negative charges cancel each other so that the plasma, taken in bulk, is electrically neutral. But because its constituents are electrically charged, they interact with magnetic fields. Thus a magnetic field can channel a plasma or even bottle it up as is done in hydrogen fusion experiments. Alternatively, an energetic plasma can grab magnetic fields and drag them along with it, as happens when the solar wind of plasma from the sun carries magnetic fields along.

Earth's magnetosphere is roughly the region where Earth's magnetism is strong enough to deflect the solar wind. On the windward - that is, sunward - side of this planet, this region lies inside a bow shock that, like the bow shock in front of a boat, forms at a distance of about 14 to 16 Earth radii where the solar wind is deflected. On the leeward side, the solar wind drags out the region into a long magnetotail that extends over a thousand Earth radii, well beyond the moon's orbit. The two doughnut-shaped radiation belts of trapped charged particles lie well inside the magnetosphere. They girdle the planet, respectively, at distances of 1.5 and 6 radii from Earth's center.

CRRES now travels through part of this magnetically controlled environment on an orbit looping between 240 miles and 21,000 miles. It comes low enough to study auroras, goes high enough to be in the magnetosphere, and regularly passes through both radiation belts.

CRRES is the first of a 1990s generation of magnetospheric explorers. Among its successors are the NASA-Japan Geotail spacecraft to be launched in July 1992 to sample the geotail from eight to 220 Earth radii and the European Space Agency Cluster project. Cluster plans to launch a quartet of satellites in September 1995 to obtain three-dimensional measurements of magnetosphere phenomena.

A major incentive for all this research is that magnetic-controlled plasma is common throughout the universe. The magnetosphere is a handy laboratory where this can be studied.