Word: cometted
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Scientists long ago recognized that every comet has not one but two tails, not always visually distinct, both extending millions of miles by the time the comet has moved close to the sun. They now know that the yellowish, often curved tail is composed of dust particles released during sublimation and swept away from the sun by the pressure of solar radiation. Sunlight reflecting off the tail produces the fiery effect. The second, bluish appendage is called the plasma or ion tail. It is formed when gases from the comet's nucleus become charged by solar radiation and then react...
...Giotto could be as much as 6,000 miles off the route projected to take it within 300 miles of the snowball. That much of an error could send it either too far from the nucleus to get the desired results or crash it into the comet. Says ESA's Bonnet: "This is going to be the most difficult observation ever made in interplanetary space...
...survival, and with good reason. The dust particles around the nucleus are expected to strike Giotto with such great velocity that a speck weighing a tenth of a gram would penetrate an aluminum plate about 3 in. thick. To prevent damage, the side of the craft facing the comet is covered with a double shield, one made of aluminum and the other of Kevlar, the material used in bulletproof vests. Even then, Giotto is not expected to survive the encounter unharmed. A collision with a large dust particle or small meteoroid could ruin the entire operation. "The biggest danger...
...photograph once every four seconds. The pictures will be instantly transmitted to earth and shown live on television. Mass spectrometers will analyze the composition of the dust from the nucleus, and other instruments will examine the properties of the ions in detail and measure the magnetic field girdling the comet's head. To prevent contamination of the surrounding space by the exhaust from Giotto's thrusters, controllers will turn off the engines at least 24 hours ahead of time. Says David Dale: "We don't want to come away from the encounter convinced that the comet is made of hydrazine...
Indeed, superstition about comets has persisted into the 20th century. As Halley's came into view in 1910, some residents of Chicago prepared themselves for death by cyanogen-gas poisoning when, as it was widely predicted, the earth passed through the comet's tail. As recently as 1970, Vietnamese peasants quaked at the sight of the "Sky Broom," the unexpectedly vivid passage of Bennett's comet...