What Is an Asteroid?
Asteroids are small, rocky celestial bodies in the Solar System, located primarily between the orbits of Mars and Jupiter. Their number is measured in the millions, and most of them are concentrated in a region known as the Asteroid Belt.
In planetary science, asteroids are sometimes referred to as “minor planets” or “planetoids.” These terms describe Solar System objects that are smaller than planets and moons.
Asteroids are remnants of material left over from the formation of the Solar System about 4.5 billion years ago. In other words, they are the “cosmic building materials” that remained after the planets were formed.
Types of Asteroids
Asteroids are divided into three main classes based on their composition:
C-type asteroids (chondrites)
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Composed of clay and silicate rocks
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The most common type
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Formed farther from the Sun
S-type asteroids
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“Stony” asteroids
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Made of silicate rocks and mixtures of nickel and iron
M-type asteroids
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Composed mainly of metallic nickel and iron
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May be remnants of the metallic cores of early Solar System bodies
These types indicate the distance from the Sun at which they originally formed.
Interesting Facts About Asteroids
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Asteroids help scientists understand how the rocky planets of the Solar System formed.
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Approximately 100 tons of material from asteroids and comets enter Earth’s atmosphere every day.
Most of it burns up due to friction. The fragments that reach the surface are called meteorites. -
Asteroid impacts were much more common in the distant past.
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About 65 million years ago, a large asteroid impact contributed to the extinction of the dinosaurs (although other factors also played a role).
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Earth may collide with an object the size of a football field approximately once every 2,000 years.
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Meteoroids about the size of a car enter Earth’s atmosphere roughly once a year.
They usually burn up, creating a spectacular “fireball” effect, and do not reach the ground. -
Some asteroids are rich in water and valuable metals.
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Some asteroids are actually remnants of comets that have lost their ice.
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Some asteroids even have their own moons.
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Most asteroids orbit the Sun between Mars and Jupiter.
Near-Earth Asteroids (NEO and PHA)
Some asteroids can approach Earth’s orbit. These objects are classified as:
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NEO (Near-Earth Objects)
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PHA (Potentially Hazardous Asteroids)
Small objects typically break apart in the atmosphere.
Larger objects, however, could impact the surface or oceans and cause serious damage.
Scientists continuously monitor these objects, map their orbits, and attempt to predict possible collisions in advance. At present, the probability of a large asteroid striking Earth is very low.
Famous Asteroids
1 Ceres
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Diameter of approximately 952 km
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The largest object in the Asteroid Belt
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Has a rocky core and an icy outer layer
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May contain a subsurface ocean
2 Pallas
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Diameter of approximately 544 km
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Has a highly irregular shape
3 Vesta
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About 580 km in diameter
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Has a bright surface
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Considered a remnant of an early protoplanet
Conclusion
Asteroids are not merely space rocks. They:
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Preserve the history of the Solar System’s formation
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Help explain how planets were formed
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Assist in understanding potential future space hazards