STONE AND IRON FROM SPACE

METEORITES ARE ALL ROCKS FROM SPACE, but they are not all alike. The meteorites known as irons, for example, are more than 98 percent metal. Those known as stony-irons are a mixture of metal and rock. But the most common meteorites are stones, which could easily be mistaken for ordinary rocks from Earth.

STONES: MELTED OR UNMELTED

Stony meteorites fall into two main groups: those that partially melted while they were in space, and those that did not melt.

Unmelted stony meteorites, the more common type that includes Estacado, are the oldest rocks formed in our solar system. These ancient stones offer a record of the solar system in its infancy.

Partially melted stony meteorites, the rarer type, show that when planets and asteroids melted, they separated into metal and stony parts.

OLDER THAN EARTH

The stony meteorite Estacado is older than Earth. If you touch the dark, round spots, you can feel the solid particles from which the solar system formed more than four billion years ago. The flat surface of Estacado has been cut and polished, revealing tiny bits of iron mixed in with the stone.

THE STUFF THAT STARS ARE MADE OF

Stars and their planets form in large clouds of gas and dust like the Orion nebula shown here. The oldest meteorites contain material from the nebula in which our solar system formed some 4.6 billion years ago.

IRONS: THE CORE OF THE MATTER

Almost every iron meteorite comes from the iron center, or core, of an asteroid. The iron core formed when the asteroid melted. During melting, the liquid iron separated, sank to the asteroid's center and hardened.

METAL FROM SPACE

The iron meteorite Gibeon was once part of an asteroid's iron core, before the asteroid broke apart in a collision with another asteroid. When the meteorite hit Earth's atmosphere, it heated up, becoming a glowing fireball. The black, pitted crust formed when the meteorite's outer layer melted in flight.

METEORITES IN THE DESERT

Only about one in 25 meteorites is an iron meteorite, but until recently irons accounted for about a third of all collected meteorites. Irons are more durable than stones, and they are easier to spot. During the 1970s, people began finding more stony meteorites by searching in the Sahara Desert and Antarctica. Both stones and irons are easy to spot against bare expanses of ice or sand. The stone meteorite Acfer 353 was discovered in 2001 in southern Algeria.

IRON OF HEAVEN

The ancient Egyptians used a hieroglyphic symbol for iron meteorites, which they called "iron of heaven." Meteorites were the main source of iron used by ancient peoples, because unrusted iron metal is extremely rare on Earth.