What are asteroids?

Asteroids are essentially remnants of the primitive building blocks that created the terrestrial planets in our solar system. Scientists believe that asteroids have not changed very much since the time they were formed, making them cosmic time capsules that can reveal how planets like our own world formed.

In addition, asteroids are thought to contain organic molecules like amino acids—the basis for proteins and DNA—leading to speculation that a meteorite from an asteroid could have seeded the early Earth with the building blocks of life.

Despite what Hollywood movies may lead us to believe, the risk of a collision between an asteroid and Earth is extremely small. NASA's Center for Near-Earth Object Studies regularly monitors the orbits of near-Earth asteroids and calculates their risk of impact within the next 100 years.

Asteroids – Infographic
Asteroids – Infographic - Text version

What are they? Asteroids are small rocky or metallic bodies that orbit the Sun. They can range in size from less than 1 cm to hundreds of kilometres. Some asteroids have their own moons. Asteroids are leftovers from the formation of our solar system 4.6 billion years ago.

What are they made of? They are made of rock, metals, and other materials. Some even contain water!

There are three common types: Carbon-rich, rocky, and metallic. Carbon-rich asteroids are dark, contain carbon, and look like charcoal. Rocky asteroids have a stony texture, contain silicate materials and iron, and look like dark rocks. Metallic asteroids have a shiny appearance, contain nickel and iron, and look like steel.

Where are they? Near-Earth asteroids are located 150 million km from the Sun. Most asteroids are located in the Main Belt, between Mars and Jupiter, 330 to 480 million km from the Sun.

Why do we study them? We study asteroids to learn what types of materials existed billions of years ago in order to understand the formation and evolution of the planets. Some of the material trapped inside asteroids might be the building blocks of life.

Credit: Canadian Space Agency

OSIRIS-REx is Canada's first participation in an asteroid sample-return mission. Using Canadian instrument OLA, the spacecraft will create a 3D map of Bennu's surface, allowing scientists to select a sample site. Canada will receive a portion of the asteroid material.

Check out this video to learn what asteroids are and what they can teach us about the earliest days of our solar system. (Credit: Canadian Space Agency)

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