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 Meteorite Origins


Meteorites have their origins in the larger bodies of the solar system. They come from asteroids and from the surface of the Moon and Mars.

Most meteorites come from asteroids, the remnants of smaller planetary bodies that formed at the same time, and out of the same basic material, as Earth and other rocky planets. Many of these “mini-planets” were shattered by collisions with one another. Asteroids are the debris. Countless numbers of them orbit through interplanetary space. Most are found between Mars and Jupiter in the Asteroid Belt.

Most Asteroid Belt objects are not a threat to us because they tend to stay in their orbits around the Sun. Occasionally, a collision knocks one toward Earth. There are more than a thousand of these Earth-approaching asteroids. If one were to hit our planet, it could cause a catastrophe like the one that killed the dinosaurs. Fortunately, these are rare occurrences. Tiny chips of asteroids, however, fall through our atmosphere all the time.

image of calirnia with vestaAsteroids are much smaller than Earth. Vesta is about 320 miles (515 km) in diameter, and it looks much like it did when it first formed. City-size Ida was once part of a larger asteroid smashed in a collision.

Meteorites From Asteroid Vesta

rocks

Only a few meteorites can be linked to a specific asteroid. These probably fell to Earth from Vesta, which formed when the solar system was very young. It has the same rocky composition as Earth, and evidence of ancient lava flows on its surface.

Smaller Asteroids

rocks

Each of the asteroids modeled here was photographed by passing spacecraft or imaged by radar. The differences between them tell us about their compositions and histories. Most asteroids are fragments of the original mini-planets. Their battered surfaces, strange shapes, and erratic movements are clues to the collisions they have experienced since forming. Mathilde is darker then charcoal and irregularly shaped. Ida is a lumpy, cratered asteroid with its own tiny moon, Dactyl. Oddly shaped Eros was the first asteroid visited by a spacecraft. Asteroid Gaspra was once part of a larger object and is covered with craters. Toutatis has a smooth surface, is a big as a city, and tumbles wildly through space.

Thousands of pieces of the sky rain down on a small city in Mexico.

big rock

On February 8, 1969, a blue-white fireball streaked across the early-morning sky above rural northern Mexico. A tremendous explosion followed, as a piece of space rock weighing several tons broke into bits. As the fragments fell, the commotion woke up the villagers of Pueblo de Allende. Soon people began gathering samples of what came to be known as the Allende meteorites.

The Village was not far from Houston, so the meteorites were taken to NASA’s Johnson Space Center. The fall occurred just before astronauts brought back the first Moon rocks, and NASA scientist were still testing ways to analyze lunar samples. The Allende samples were a perfect test of their methods, using real space rocks. To everyone’s surprise, the meteorites turned out to be the same kind of rock that formed the inner planets and asteroids. This discovery revealed what the material in the early solar system was like.

Allende and the Early Solar System

Allende meteorites are pieces of very ancient solar system history. They contain some of the rocky material that existed before the planets and asteroids formed. The presence of these materials tells scientists that meteorites like Allende have not melted since the birth of the solar system, more than 4 billion years ago.

What Do You See? © A. J. Higgs, Maltbie, Inc.

Pieces of Solar System History

The polished slice of Allende meteorite in the microscope (left) is a piece of the very early solar system. This specimen contains chondrules. They formed from dust grains that existed in the cloud of gas and dust where the Sun and planets were born. These grains melted and cooled to make the tiny beadlike spheres you see here. Rock fragments and other materials are also mixed with the chondrules. All these ancient building blocks combined in the solar system’s birth cloud to form ever-larger rocky bodies that ultimately became the asteroids and planets.

Pieces From Another World

Meteorite From Mars

rockThis Billion-year-old rock comes from a lava flow on Mars. About 20 million years ago, an object hit the planet and blasted pieces of the hardened lava into space. This one fell to Earth about 600,000 years ago. It was found in the desert of Oman (in the Middle East) in 2000.

Now do we know it came from Mars? Scientists study gases trapped inside meteorites they think are from the Red Planet. They compare their results to data taken by the Viking landers on Mars in 1976. Samples that match are probably from Mars.

Meteorite From the Moon

rockThis chip from the Moon’s surface is a mixture of many kinds of rock and fragments of lava that melted together. A meteorite impact sometime in the distant past knocked it off the Moon’s surface. It fell to Earth and was found in Oman in 2002.

Astronomers analyzed the chemical elements in this meteorite and those in rocks brought back from the Moon by the Apollo astronauts. Since it matches the elements and minerals in the Apollo samples, we know this meteorite also came from the Moon.