Word: earthly
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Dates: during 1950-1959
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...more speed, would have swooped past Mars and soared out toward the asteroids. George Paul Sutton, professor of aeronautical engineering at M.I.T., believes that present propulsion systems with a little refinement can send a space vehicle as far as Jupiter or even to Saturn, 750 million miles from the earth...
Astronomers can hardly wait for the day when these first space scouts are launched. For oddly enough, they know less in many ways about the planets, the earth's neighbors, than they do about far-distant stars. The reason is that stars shine in their own light, revealing much about themselves to astronomers' spectroscopes. The solar system's planets are visible only in the reflected light of the sun. Their spectra carry little firm information, and the details that can be seen on their surfaces are clear enough to excite but too vague to satisfy human curiosity...
Dutch-born Astronomer Gerard Kuiper (rhymes with hyper), head of the University of Chicago's Yerkes and McDonald observatories, thinks the moon was formed at the same time as the earth (5½ billion years ago), but at first it revolved only about 20,000 miles from the earth's surface. Beyond it were a lot of smaller satellites arranged in a disk somewhat like the rings of modern Saturn...
This situation did not last. When the earth acquired oceans, the great tides aroused in them by the nearby moon made the earth rotate more slowly. This made the moon spiral outward. As it moved, it crashed into the lesser satellites, each of them blasting an impact pit in its surface. The bigger pits punched through the moon's crust and were filled with lava from the molten interior. The biggest satellite of all, about 100 miles in diameter, hit the present site of the lunar plain called Mare Imbrium-the right eye of the "man in the moon...
There is no water on the moon, so Gold's erosion cannot be like the kind that wears down earth's mountains. He thinks that the chief eroding agent is high-energy radiation from the sun helped by cosmic rays and meteorites. They slowly chewed a flour-fine dust from the moon's exposed rocks and kept it stirred up so that it gradually flowed into low places like the interiors of old craters and the maria...