February 1985 Archives

ISEE-3/ICE Comet Giacobini-Zinner Handbook

The Comet Giacobini-Zinner Handbook, An Observer's Guide to the first comet to be explored by a spacecraft, NASA JPL 14 Feburary 1985, PDF

Comets have been feared and misunderstood throughout most of recorded history, partially because of their peculiar and often spectacular appearance and infrequent apparitions. They were considered by many to be omens of bad tidings, While no longer widely feared, comets remain misunderstood and are, perhaps, the least-understood members of our solar system. Comets are thought to be composed of a primitive collection of ices and dust. They may be invaluable remnants from the primordial mixture from which our solar system formed some 4.5 billion years ago.

Comets also display many fascinating features and undergo remarkable interactions with their environment, such as often producing a very long tail. One facet of this interaction is in the domain of plasma physics, the branch of science that studies electrified gases and magnetic fields. Most of the matter in the universe is in the plasma state. The coordinated exploration and study of Comet Giacobini-Zinner should provide important advances in our knowledge of cometary plasma physics. Comet Giacobini-Zinner is coming, and so is Comet Halley, the most famous of comets.

Thousands of professional and amateur astronomers are planning to study Halley's Comet under the aegis of the International Halley Watch, which is coordinating and archiving ground-based observations made in various wavelengths using many different techniques. The purpose of this Handbook is to alert the observing community to the parallel opportunity to observe Comet Giacobini-Zinner and to enhance the scientific return from the intercept by the International Cometary Explorer (ICE) spacecraft.

While the mission to Comet Giacobini-Zinner will be the first direct comet exploration, the mission should not be considered entirely by itself. The missions to Comets Giacobini-Zinner and Halley are complementary and synergistic. The ICE encounter will take place on September 11, 1985, some six months before the spacecraft arrive at Halley's Comet in March of 1986. In so doing, valuable experience in terms of in situ sensing in a cometary environment will be obtained, in addition to the first, possibly serendipitous scientific results.

The ICE spacecraft will pass through the tail on the anti-sunward side of the nucleus, while all the Halley missions are planned to pass on the sunward side of the nucleus. Neither Halley nor Giacobini-Zinner will be a prominent sight to the casual observer, and most of the waiting public may be disappointed. However, the rewards, almost surely, will be spectacular scientific discoveries. These comets are now serving as the focal point for an unprecedented level of international scientific cooperation.

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