Visitor from Space?

Meteors, most astronomers think, are merely junior members of the solar system--fragments of comets or wandering bits of a blown-up planet. But a few experts still cling to the more romantic theory that some meteors hit the earth after traveling across interstellar space, perhaps for billions of years, from some other part of the Milky Way galaxy (of which the solar system is a part).

One such learned romanticist is Dr. Lincoln La Paz, of the University of New Mexico. Last week Dr. La Paz announced his conclusion that a 600-lb. meteorite recently dug up near Ardmore, Okla. is probably one of these rare visitors from interstellar space.

Speed Limit. Part of the debate about meteors concerns their speed. If they are true members of the solar system, they must travel, like the planets and comets, on "closed orbits," again & again round the sun. In this case, says La Paz, their velocity can never be greater than 26.1 miles per second. If a body exceeds this limit (the "escape velocity" at the distance of the earth), it will leave the solar system and never come back.

This principle works just as well in reverse. If a body is moving faster than 26.1 miles per second, it cannot be a permanent member of the solar system. It must be a visitor from space, bound for space again on an "open," one-time orbit.

Most meteors move much more slowly than the limit, but La Paz believes that a few well-observed fireballs were traveling faster than would be possible if they were following orbits around the sun.

Now he hopes that the Oklahoma meteorite will clinch his case. The established theory is that meteorites were parts of a broken-up planet. Some of them are made of stony material; some are metallic, mostly iron and nickel. A few are mixtures of stone and metal.

This varied composition is explained by assuming that the planet they came from was molten inside. The heavy metal in it had sunk toward the center. The lighter stony stuff had risen toward the surface. In between was a zone containing both metal and stone. So when the planet blew up, its fragments might be either metal or stone or a mixture of both.

Strange Stuff. The weakness of this theory is that all meteorites should show signs of having solidified from the molten state. Most of them do, but a very few (only three or four) are classified as "granular hexahedrites." They are made of iron and nickel, says La Paz, but the material is not homogenous and crystalline, as it would have to be if it had solidified from a liquid. Instead, the strange material from space is slapped together haphazardly in irregular gobs.

Last week the Ardmore meteorite was carefully analyzed. It proved to be a genuine granular hexahedrite, and there is enough of the odd stuff for all sorts of experiments, which may prove the La Paz contention: that the meteorite could never have been formed from the molten inside of a defunct planet. It may have been formed in some other way deep in interstellar space, or in another planetary system around some foreign star.

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