SPACE ROCKS

Meteorites are rocks that fall to Earth from space.

Many rocks travel the Solar System on paths that are destined to collide with the Earth. A rock that survives its fall through the Earth's atmosphere and lands on the surface of the Earth is called a meteorite.

Every day, many tonnes of material fall to Earth from space. The number of pieces of rock that falls each year drops as the size of the rock increases. Most of the material is in the form of tiny specks of dust, and we do not notice it. Thousands of meteorites weighing about a kilogram fall to Earth every year, but only five or six of these will be recovered – for example if they fall through the roof of a house. Huge meteorites weighing several tons that make craters on the Earth's surface are rare events that only take place every few thousand years.

[pictured above] Asteroid meteorite (Pasamonte). This rock started its journey on an asteroid, then traveled millions of kilometers over millions of years before it crashed into the Earth. The black surface is fusion crust that formed when the meteorite fell through the Earth's atmosphere.
 
 

ARMCHAIR EXPLORING

Meteorites come from asteroids, the Moon and Mars.

Meteorites come from parts of the Solar System that we have never explored. We can study the geology of many distant places without the expense and risk of returning samples to Earth from space missions.

The only extraterrestrial rocks that have been returned to Earth to date (2006) are rocks from the Moon. Although Mars is being explored intensely, we have not yet brought rock samples back from the Red Planet. Most meteorites come from asteroids. We currently have samples of about 120 different asteroids in the form of meteorites. The first pieces of an asteroid (asteroid Itokawa) will be returned to Earth by the Japanese Hyabusa spacecraft in June 2007.

[pictured above] Martian meteorite (Zagami). This is one of about 30 meteorites known that is a piece of Mars. The rock is a basalt that flowed from a volcano on Mars about 180 million years ago.
 
 

TIME CAPSULES

The oldest rocks in the Solar System are meteorites.

Meteorites called chondrites contain the first pieces of dust that formed in the Solar System. The oldest rocks are 4.6 billion years old. This is how we know the age of the Solar System.

Because asteroids are small, they were only geologically active for a few million years after they formed. Meteorites from asteroids are mostly rocks that formed more than 4.5 billion years ago. Since then, they have been affected by impacts on asteroid surfaces, but much of their ancient history is preserved. Meteorites teach us about the early stages of formation of the Solar System.

[pictured above] Chondrite (Allende). The round objects are called chondrules. Chondrules are tiny rocky balls that formed 4.6 billion years ago. The Earth and other planets might have begun to form from tiny pieces of rock that looked like this chondrite.
 
 

DETECTIVE WORK

Scientists around the world study meteorites to learn about the Solar System.

We learn a lot of different things from meteorites. The amounts of each of the chemical elements in certain meteorites are used as a measure of the composition of the entire Solar System. Minerals in meteorites are used to understand temperatures and pressure at which they formed. The ages of meteorites are used to fit together the story of how the Solar System evolved. Meteorites also carry a story of how asteroids collide and break apart, flinging material through space.

Scientists at the University of New Mexico are part of the international community that works hard to learn as much as possible from meteorites and other extraterrestrial material. We use powerful electron microscopes and chemistry laboratories that measure abundances of elements and isotopes with very high precision. By looking through microscopes, at tiny pieces of material, we contribute to mankind's knowledge of the immense Solar System that is our home.

[pictured above] A scientist using the ion microprobe at the University of New Mexico. The ion microprobe is a type of mass spectrometer used to analyze mineral grains in rock samples.
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