Word: planet
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Dates: during 1950-1959
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Last week Astronomer Gerard Peter Kuiper (rhymes with piper) of the University of Chicago made another move toward demoting Pluto. Recent observations have proved that its period of rotation on its own axis is more than six days (TIME, Feb. 6). For a planet, says Scientist Kuiper, this is too slow...
Astronomers have always felt uncertain about Pluto, the outermost planet in the solar system. It is suspiciously small, with less than half of the earth's diameter, and its orbit is peculiar. Instead of revolving in a near-circle around the sun as the other planets do, Pluto follows an eccentric ellipse, cutting across the orbit of Neptune, its sunward neighbor (which is 39 times the size of the earth). These deviations suggest that Pluto may not be a real planet...
Most astronomers now think that the sun and its planets were once a great cloud of gas and dust which gradually condensed around a central mass. That mass became the sun. As the gas cloud grew smaller and denser, some of its material spun out to form a flat disk. After a billion years or so, the disk broke up into loose blobs called protoplanets. Each of these contracted independently, forming its own core. Any material left outside eventually turned into satellites revolving around a planet...
...Kuiper thinks that Pluto is an escaped satellite that once revolved around Neptune. The other satellites of Neptune, Triton and Nereid, may have escaped too, but eventually were recaptured. They tangled with the gaseous envelope that still surrounded the mother planet and were reduced again to the satellite status. Pluto, however, managed to keep its freedom until the sun had dissipated most of Neptune's gaseous envelope. Now it is probably safe for the life of the solar system...
...must say, it sounds like rather a cute idea." Bok praised Kuiper as "the custodian of the Solar System. Whenever he says something, you'd better listen to him." Bok added, "Although Kuiper's theory makes a good deal of sense, I still consider Pluto as a genuine planet. It certainly is queer duck, though...