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 Credit: NASA/JPL-Caltech |
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Nov 05, 2004 Human beings are children of the Earth, a wet and rocky planet. Our senses are adapted to wind and water and stone. When we try to understand the rest of the universe, we naturally relate our observations to what we already know about gasses and liquids and solids. Our theories of gasses and liquids and solids have enabled us to build machines that extend our senses: We can "see" x-rays; we can "taste" voltage differences; we can 'smell' elements; we can 'touch' the interior of the Earth; and we can 'hear' the radio whisperings of the planets. We can propel our machines into space, to sniff the solar wind, to taste the Martian rocks, and to peer beneath the veil of Titan's atmosphere. The above photo of the Cassini probe illustrates how human and more-than-human senses have been sent into space to learn more about Saturn, its rings, its moons, and its environment. Our new senses have discovered another component of nature, one that arises from electricity. Because our natural senses don't react to electricity directly, we've not understood the importance of this other component in the cosmos nor have our theories taken it into account. But now we've discovered that it makes up 99 percent of the
visible That component is plasma. Plasma is a mixture of charged and neutral particles. This makes it an excellent conductor of electricity. Moving charged particles are electric currents, and electric currents generate magnetic forces. Those forces pinch the currents into filaments. The filaments carry electrical power around circuits that can encompass large volumes of space. The moving charged particles also bunch up into capacitor-like "double layers". These double layers concentrate electric fields, partition space into cells, and emit microwaves and x-rays. Space probes such as Cassini sense these activities of plasma: Saturn's auroras, changing patterns of thunderstorms, disappearing spokes, ring ripples, radiation belts in the rings, Titan's atmosphere stretched and accelerated around its orbit. But we lack theories with which to understand and to utilize plasma. Our familiar mathematical metaphors derived from wind and water and stone are inadequate. We must familiarize ourselves with the neglected explanations of plasma from Birkeland, Langmuir, Alfven, and their colleagues. We need to develop those nascent explanations into quantitative theories based on further observations and experiments. Just as the empirical theories of gasses and liquids and solids enabled us to build machines that extended our senses to the planets, the new theories of plasma can enable us to build machines that will take our new senses to the stars.
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