Word: planets
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Dates: during 1940-1949
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...believed to be part of the solar system. A few of the micro-meteorites floating gently down, said Whipple, may be the only specimens available of "interstellar solids." Geologists should look for micro-meteorites, Whipple said, in places like the Cretaceous chalk beds. Many astronomers believe that a planet blew up fairly recently; if so, there ought to be strata rich in its micrometeorite fragments to date the explosion...
...proto-planets" (as Kuiper calls the eddies) condensed into planets, each with a disc of loose material around it. Then the planets' discs turned into satellites. One planet, Saturn, retains part of its disc as the famous rings...
Cousins in Space? Kuiper does not think that the earth's satellite, the moon, was formed in this way. The earth-moon pair, he thinks, is a double planet, formed when the planets were formed. The pockmarks on the moon's face were made by material raining down from the double planet's common disc. The earth must have had similar marks, originally, he thinks, but since it was big enough to hold an atmosphere, the marks were erased long ago by wind-and-water erosion...
...solar system swarms with asteroids (probably fragments of a shattered planet), but the new-found asteroid is extraordinary. Instead of being almost circular, its orbit is a long ellipse. Revolving around the sun in about 360 days, it passes inside the orbit of Mercury and comes within 22 million miles of the sun. Then it recedes to 156 million miles, beyond the orbit of Mars. No other known asteroid visits both places...
Astronomers think that the new asteroid will prove a useful tool in their unearthly studies. Since it comes close to Mercury, it will help them measure (by changes in its orbit) the mass of the planet, which is not known very exactly. "But [an asteroid] is rather like a concerto," explained Dr. Richardson. "It has no real practical value...