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Comet exploration

Sep 07, 1985

In 1985, the International Cometary Explorer (ICE) flew relatively unscathed through the gas tail of comet P/Giacobini-Zinner, at a speed of 21 km/sec at its closed approach of some 7,800-km downstream from the nucleus. The spaceraft found a region of interacting cometary and solar wind ions, and encountered a comet plasma tail about 25,000 km wide. Water and carbon monoxide ions were also identified, which confirmed the “dirty snowball” theory proposed by Fred Whipple (1950). It had been launched on 12 Aug 1978, originally named ISEE-3 (International Sun-Earth Explorer), then renamed ICE when, after completing its original mission in 1982, it was gravitationally maneuvered to intercept the comet.