Where did AMPTE's ions go?

Where did AMPTE's ions go?

In 1984 and 1985, an unusual family of satellites called the Active Magnetospheric Particle Tracer Explorers (AMPTE) produced a series of "artificial comets" by releasing barium and lithium atoms into Earth's magnetic field, so that the atoms would be ionized by the sun's ultraviolet light and behave like the tails of natural comets. The experiments produced glowing, comet-like clouds as expected (SN: 7/27/85, p.54), but scientists were puzzled when one of the satellites sent along specifically to sample the ions farther down the "tails" failed to detect any.

In the May 1 JOURNAL OF GEOPHYSICAL RESEARCH, researchers describe their attempt to understand where the missing ions went, based on a hypothesis they first proposed a year ago. John B. Cladis and William E. Francis of the Lockheed Palo Alto (Calif.) Research Laboratory suggest the ions from the first of two barium releases were carried along and across the lines of Earth's magnetic field into the shape of a narrow corridor that brought them no closer to the satellite than about twice Earth's radius. The second ion supply, they say, got no closer than three Earth radii.

As for the lithium, those atoms take much longer to become photoionized, so they expanded into a very large volume, and the ions were detected within this volume over a broad time interval. The slow ionization, however, provided enough time for the lithium cloud to become extremely rarefied. Unfortunately, the satellite's most sensitive detector had stopped working by that time, and the numbers of lithium ions had gotten too low to be measured by the detectors that were still operating.

Scientists plan a similar but more elaborate experiment with the NASA/Air Force Combined Release and Radiation Effects Satellite, carrying barium, lithium and other materials.