21P/Giacobini–Zinner
Giacobini - Zinner ( official name 21P/Giacobini-Zinner ) is a short-period comet that was examined on 11 September 1985 by the spacecraft ICE (International Cometary Explorer). He is thus the first comet that has ever been explored by a probe.
Discovery
The comet was discovered on December 20, 1900 by Michel Giacobini. Although the orbit determination indicated that there must be a short-period comet, the comet remained unobserved in its predicted for the 1907 return. His next recurrence had initially expected for the year 1914, but after Ernst Zinner had tracked an unknown comet on October 23, 1913, it turned out that this is identical to Giacobinis Comet of 1900. The comet bares the name of the two explorers.
Orbit
Giacobini - Zinner runs barely on an elliptical orbit around the sun, the sun next point ( perihelion ) outside the orbit of the earth is. The sonnenfernste point ( aphelion ) is located just outside the orbit of the planet Jupiter, which marks him as a short-period comets of the Jupiter family.
Particularly noteworthy was the perihelion passage in 1946, since that time the comet passed by the Earth in just 0.26 astronomical units away. The comet reached this brightnesses in the seventh size class.
The comet is the parent body of the meteor shower of Giacobiniden.
Spacecraft ICE
Only about half a year before a fleet of various space probes explored the Halley's comet in the spring of 1986, flew on 11 September 1985, the spacecraft ICE (International Cometary Explorer) 7800 km away from the comet head by the tail of Giacobini - Zinner. He is thus the first comet that has ever been explored by a probe. The spacecraft, which was originally designed under the name of ISEE 3 for the exploration of the solar wind shortly before reaching the magnetic field of the earth, was able to examine the interaction of the solar wind and the interplanetary magnetic field with the tail of Giacobini - Zinner. A camera for taking pictures was not on board. It was found that the influence of the comet was bigger than expected, and that the magnetic field of the solar wind changed direction, as ICE happened in the middle of the tail. A clear bow shock upon impact of the solar wind on the sphere of influence of Giacobini - Zinner could not measure ICE.