Stones From Space Help (page 3)

By — McGraw-Hill Professional
Updated on Sep 17, 2011

What Are Meteoroids Made Of?

There’s only one way to tell what space rocks are made of, and that is to find meteorites and analyze them. This has been done with plenty of rocks from space. They have been smashed, cut, examined under microscopes, subjected to ultraviolet radiation, heated, cooled, and generally worked over in every conceivable way. Three main types of meteorites have been identified: aerolites (stony), siderites (metallic), and tektites (glassy).

Aerolites bear some resemblance to rocks of Earthly origin. They are made up largely of silicate material and can range in size from pebbles to boulders. The siderites are composed mainly of iron and nickel. Some meteorites are stony with flecks or bands of metal. When a meteoroid enters the atmosphere, the heat of friction causes the outer part of the object to melt. This produces a glassy appearance on the exterior of an aerolite and can blacken the metal on the exterior of a siderite.

Aerolites and siderites are believed to be material left over from the primeval Solar System—stuff that never congealed into planets. If this is true, then they originated in the cores of stars that exploded billions of years ago and scattered their matter throughout the galaxy. This is the only explanation for why these objects exist; otherwise, interstellar space would consist almost exclusively of hydrogen and helium gas. It takes the extreme temperatures inside stars to produce the nuclear fusion reactions that give rise to heavier elements such as silicon, iron, nickel, sulfur, and all the rest.

The tektites tell a different story. These odd, glassy stones resemble rocks of volcanic origin, as if they are parts of a planetary crust or mantle that melted and then solidified again. Tektites have been found in places nowhere near Earthly volcanoes, and they differ dramatically from the composition of the Earth’s crust in their vicinity. Because of this, astronomers believe that they came from space. However, they differ from aerolites and siderites in an important way besides their appearance and composition: They are much younger. According to one theory, the tektites were created by one or more catastrophic asteroid impacts on the Moon, events that hurled moon rocks upward with such speed that they escaped the gravitational field of the Moon. Some of these objects, if this took place, would be captured by the Earth’s gravitation and would fall to our planet like meteors and meteorites.

The Moon has many craters with prominent rays extending hundreds of kilometers outward. These rays were produced by material ejected from the craters when the impacts occurred. If Moon rocks could be thrown that far, they also could be thrown into orbit or into interplanetary space. The prominent crater Tycho has been suggested as a logical candidate for the production of some of the tektites that have been found on Earth.

Recently, objects similar to tektites have been found that are thought to have originated on Mars. It would take a more violent asteroid strike to throw matter into interplanetary space from Mars than it would from the Moon, but calculations show that it is possible. From a statistical standpoint, it is reasonable to suppose that such an event has taken place at least once within the past few million years. After all, scientists believe that only 65 million years ago an asteroid splashed down in the Gulf of Mexico with such force that the resulting environmental disturbances wiped out more than half the Earth’s species, including the dinosaurs, and irrevocably shifted the course of evolutionary history.

Practice problems of this concept can be found at: Comets, Asteroids, and Meteors Practice Problems

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