FIGURE 2.1 A photograph of the nucleus of Halley's Comet taken by the Giotto spacecraft. Comets are thought to contain samples of the primordial material out of which the solar system formed 4.5 billion years ago. Complex organic molecules found in the material boiled off from Halley. Reprinted by permission from H.U. Keller. Copyright © 1986 Max-Planck-Institut für Aeronomie.

Flyby spacecraft, observatories on the ground such as the MMA and new 8-m-diameter optical and infrared telescopes, in airplanes such as the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA), and in orbit about the earth such as SIRTF will determine the size, distribution, and composition of comets as far away as the orbit of Jupiter.

Weather and Volcanoes

What forces create the climate and weather on the earth? What forces make the continents drift and volcanoes erupt? Is our climate changing because of the actions of humans? Some information on these questions comes from

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