asteroid

American  

[as-tuh-roid] / ˈæs təˌrɔɪd /

noun

• asteroids
  plural

1. 

   Astronomy. any of millions of small celestial objects revolving around the sun, often irregularly shaped and having a great range in size, from as small as 6 feet (2 meters) across to about 620 miles (998 kilometers) across: the vast majority of known asteroids exist within the asteroid belt.

2. Zoology. a starfish; an asteroidean.

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adjective

1. starlike.

asteroid British  

/ ˈæstəˌrɔɪd /

noun

1. Also called: minor planet, planetoid. any of numerous small celestial bodies that move around the sun mainly between the orbits of Mars and Jupiter. Their diameters range from 930 kilometres (Ceres) to less than one kilometre

2. Also called: asteroidean. any echinoderm of the class Asteroidea; a starfish

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adjective

1. of, relating to, or belonging to the class Asteroidea

2. shaped like a star

asteroid Scientific  

/ ăs′tə-roid′ /

1. Any of numerous small solar system bodies that orbit the Sun primarily in the asteroid belt, a region between the orbits of Mars and Jupiter. Asteroids are intermediate in size between planets and meteoroids with diameters that measure between approximately one hundred and several hundred kilometers. While more than 1,800 asteroids have been cataloged, and as many as a million or more smaller ones may exist, their total mass has been estimated to be less than three percent of the Moon's. Asteroids are thought to be left over from the early formation of the solar system, when planetesimals in a protoplanetary disk were scattered after coming under Jupiter's gravitational influence. The continuing collision of planetesimals that remained between Jupiter and Mars caused many of them to fragment, creating the asteroids that exist today.

2. Also called minor planet planetoid

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asteroid Cultural  

1. A small planet that revolves around the sun. The largest asteroid is only about six hundred miles in diameter. (See asteroid belt.)

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Other Word Forms

Derived Forms

• asteroidal
  adjective
• interasteroidal
  adjective

Inflected Forms

Nouns

• asteroids
  plural

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Etymology

Origin of asteroid

First recorded in 1795–1805; from Greek asteroeidḗs “starry, starlike”; see star, -oid

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Explanation

An asteroid is a large, irregularly shaped object in space that orbits our Sun. If one of these giant rocks ends up on a collision course with Earth, we are in for big trouble. An asteroid is like a comet. However, while comets are mostly made of ice, asteroids are made up of rock or even metal. This makes them dangerous because they can cause a lot of damage if they collide with a planet. The craters on the Moon were formed by asteroids and some think it was an asteroid that wiped out the dinosaurs. Around a million asteroids are located between Mars and Jupiter in an area called the “asteroid belt.”

Example Sentences

See Examples For:

asteroid asteroids

Bennu is considered an exceptionally primitive asteroid because its material formed approximately 4.5 billion years ago and has experienced relatively little chemical alteration since then.

From Science Daily ● Oct. 24, 2026

On September 23, 2023, a capsule carrying approximately 120 grams of asteroid material landed in the Utah desert.

From Science Daily ● Oct. 24, 2026

When scientists first identified the formation in 2002, several features suggested that it had been created by a high-speed collision with an asteroid or comet.

From Science Daily ● Oct. 21, 2026

Such changes can occur when an asteroid strikes at tremendous speed, generating powerful shock waves that pass through the surrounding rock.

From Science Daily ● Oct. 21, 2026

Any asteroid out there that has our name on it is very likely to have no other.

From "A Short History of Nearly Everything" by Bill Bryson

For years, researchers generally believed that primitive asteroids like Bennu originated in the outer Solar System, perhaps in the same distant regions where comets formed.

From Science Daily ● Oct. 24, 2026

The "capture" hypothesis, meanwhile, postulates that the moons are asteroids pulled in by Mars's gravity.

From Barron's ● Oct. 19, 2026

Or the moons are two wandering asteroids from the outer Solar System, which were grabbed by the Red Planet's gravity.

From BBC ● Oct. 18, 2026

The software is designed to model collisions involving asteroids, comets, and planets.

From Science Daily ● Aug. 26, 2026

Some stars would have no suitable planets—perhaps they would all be giant gas worlds, or tiny asteroids.

From "Cosmos" by Carl Sagan

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Related Words

• earth
• globe
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