dipper@utastro.UUCP (Debbie Byrd) (11/26/85)
The ion tail of a comet is much wider and more active than previously thought. More -- after this. November 26 Giacobini-Zinner and I.C.E. Comets have two types of tails. The dust tail is made of tiny bits of debris coming off the comet's nucleus. The other tail -- called the ion tail -- is made of electrically charged particles of gas which have also been evaporated off the nucleus. Last September, thanks to a spacecraft, we got a tremendous amount of new data about the ion tail of Comet Giacobini-Zinner. The International Cometary Explorer -- known as I.C.E. -- crossed the tail of Giacobini-Zinner on September 11. I.C.E. didn't have equipment aboard that could analyze the dust tail of the comet. That's because the spacecraft was launched originally to study the solar wind -- electrically charged gases flowing from the sun. But I.C.E.'s instruments revealed very exciting information about the ionized gases present in the tail of the comet. The ion tail was about three times wider than expected -- and the gases in the tail were very turbulent and complex. As another surprise, there was no clear evidence for a magnetic bow shock -- a sharply defined boundary marking the interface of the comet's magnetic field with the solar wind. The magnetic fields of planets like Saturn, Jupiter and the Earth have clearly defined bow shocks. After its history-making encounter with Giacobini-Zinner, I.C.E. is now targeted for another comet mission next March. The spacecraft will relay data on the solar wind before the wind interacts with a comet named Halley. Script by Diana Hadley. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin