dipper@utastro.UUCP (Debbie Byrd) (09/10/85)
Tomorrow a spacecraft will make the first visit to a comet. More -- after this. September 10 I.C.E. Encounters Giacobini-Zinner No spacecraft has ever encountered a comet. Tomorrow that'll change. The NASA spacecraft called I-C-E -- International Cometary Explorer -- is due to pass within six thousand miles of the nucleus of Comet Giacobini-Zinner. The spacecraft will fly through the comet's tail. I-C-E wasn't designed for a visit to a comet. The spacecraft was launched in 1978 and spent five years studying the solar wind -- ionized gases from the sun. After successfully completing that mission, NASA engineers in 1983 changed the orbit of the spacecraft -- and sent it chasing a comet. Giacobini-Zinner orbits the sun once every six and half years. I-C-E's encounter with this comet on Wednesday occurs just six days after the comet reached its perihelion, or closest point to the sun, on September 5th. I-C-E carries no cameras so it won't give us any pictures of the comet. Instead scientists will use the instruments that studied the solar wind to get information on the electrically charged particles in the comet's tail. Comets are iceballs of frozen gases and dust -- formed probably at the same time the rest of the solar system was forming. The dust and gases boiling off the comet are clues to the kinds of materials that made the planets. On Wednesday, we'll have a chance to gather some of those clues -- as I-C-E becomes the first spacecraft from Earth ever to visit a comet. Script by Diana Hadley. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin