40 Years Ago: The International Cometary Explorer Made History at Comet Giacobini-Zinner
A Historic Encounter
On September 11, 1985, the International Cometary Explorer (ICE) spacecraft achieved a historic first in space exploration: it became the first spacecraft ever to fly by a comet. Originally launched as ISEE-3 (International Sun-Earth Explorer 3), the spacecraft was repurposed and renamed for its cometary mission.
The Target: Comet Giacobini-Zinner
ICE targeted Comet 21P/Giacobini-Zinner, a periodic comet with an orbital period of about 6.6 years. The spacecraft flew through the comet's plasma tail, collecting valuable data about the comet's environment that scientists could not obtain from Earth-based observations alone.
Scientific Significance
This flyby represented a major leap in cometary science. By passing directly through a comet's tail, ICE gathered direct measurements of the solar wind's interaction with cometary plasma, magnetic fields, and charged particles. These observations helped scientists better understand the nature of comets and their behavior in ways that remote sensing from Earth simply could not achieve.
A Collaborative Achievement
The mission was a cooperative effort between NASA and European scientists, demonstrating the value of international collaboration in space exploration. The success of ICE paved the way for future cometary missions, including the famous encounters of the European Space Agency's Rosetta mission with Comet 67P/Churyumov–Gerasimenko decades later.