In 1978, the ISEE-3 (International Sun-Earth Explorer) was launched. After completing its original mission in 1982, it was renamed the International Cometary Explorer (ICE) when it was gravitationally manuvuered to intercept the comet P/Giacobini-Zinner. On 11 Sep 1985, it flew relatively unscathed through the gas tail of that 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 probe 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).«