What is an asteroid?

Asteroid collision (artist concept)

Asteroids typically make headline news for close calls with Earth, and occasionally, for striking our planet. These mysterious and unpredictable space rocks are not always forces of destruction, though: in fact, they may be responsible for creating planets. Scientists think that planets like our own may have formed as a result of epic collisions between asteroids and larger celestial bodies called "proto-planets," like the one depicted in this illustration. (Credit: NASA / JPL-Caltech)

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.

What's the difference between an asteroid, a comet, a meteor and a meteorite?

Asteroids are composed mainly of rock and metals, while comets are made of ice, dust and small rocks. An object becomes a meteor if it enters Earth's atmosphere. Since meteors leave visible streaks across the sky, they are often known as shooting stars. The term "meteorite" refers to solid debris that survives entry and impact with the ground.

From Comet to Meteorite! - Illustration

Text description of image

Comet, meteor or meteorite? Illustration providing an overview of the characteristics of comets, asteroids, meteoroids, meteors, fireballs and meteorites. (Credit: Canadian Space Agency)

When asteroids strike

On February 15, 2013, while the world watched and waited for Asteroid 2012DA14 to approach Earth on a close flyby, a second and completely unrelated asteroid burst through our atmosphere and disintegrated in the skies over Chelyabinsk, Russia. Although meteors are not uncommon events (in fact, an average of 100 tons of meteoroids falls on Earth daily), the surprise blast occurred over a populated area. Locals captured stunning images of the fireball breaking up over the cityscape—and the damage caused by from the shockwave that followed—and shared them extensively on social media outlets. Suddenly, understanding asteroids—especially detecting and predicting their behaviour—became headline news.

Asteroids appear to be the unruly, rebellious objects of our solar system, with seemingly bizarre orbits that occasionally bring them uncomfortably close to Earth—and, like the Chelyabinsk meteor, sometimes make them unwelcome visitors. Scientists are very interested in studying them to learn more about the evolution of our solar system, how the planets formed, and even how asteroids may have contributed to the origins of life on Earth. The Canadian Space Agency is part of NASA's OSIRIS-REx mission to return a sample of one of the most potentially hazardous known asteroids and to provide more conclusive data on whether or not it might impact Earth.

Manicouagan crater

The Canadian landscape is pockmarked with some of the largest meteor impact craters in the world, like Manicouagan crater in this photo taken by astronauts aboard the International Space Station, which is believed to have been made by an asteroid. While asteroids attract attention (and fear) for their impacts, scientists think an asteroid could actually have planted the seeds for all life on Earth. Studying an asteroid will reveal more information about how asteroids form and evolve, as well as how their orbits develop, contributing to our understanding of which asteroids may be hazardous for Earth. (Credit: NASA)

What is the Yarkovsky Effect?

OSIRIS-REx presents the new 321Science video about how sunlight can affect the orbits of small asteroids. This video explores how the Yarkovsky effect occurs and how it can change the orbits of asteroids—changing near misses to impacts or impacts to near misses. (Credit: University of Arizona)