asteroid
Americannoun
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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.
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Zoology. a starfish; an asteroidean.
adjective
noun
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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
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Also called: asteroidean. any echinoderm of the class Asteroidea; a starfish
adjective
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of, relating to, or belonging to the class Asteroidea
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shaped like a star
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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.
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Also called minor planet planetoid
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of asteroid
First recorded in 1795–1805; from Greek asteroeidḗs “starry, starlike”; see star, -oid
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.”
Vocabulary lists containing asteroid
Over The Moon: Planetary Vocabulary
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Oh, My Stars! A Solstice Sampler
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Elements of the Universe: Aster, Astro ("Star")
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
These comparisons will help the team better understand the cameras' performance before Psyche begins studying its much less familiar asteroid target.
From Science Daily ● Jul. 28, 2026
Following the successful gravity assist, the spacecraft is now traveling directly toward asteroid Psyche, which orbits in the main asteroid belt between Mars and Jupiter.
From Science Daily ● Jul. 28, 2026
This prehistoric creature has survived ice ages, the asteroid impact that killed the dinosaurs, and continental drift.
From BBC ● Jul. 27, 2026
"Covalently bonded carbon and hydrogen in comet and asteroid material are believed to have formed in the outer envelopes of stars, in high-energy events like supernovae, and in interstellar environments," Ms. Losurdo said.
From Science Daily ● Jul. 19, 2026
Even if every asteroid in the solar system had a name and known orbit, no one could say what perturbations might send any of them hurtling toward us.
From "A Short History of Nearly Everything" by Bill Bryson
The process created carbon-rich dust resembling material that floats through interstellar space and is preserved inside comets, asteroids and meteorites.
From Science Daily ● Jul. 19, 2026
Repeated gravitational nudges from Jupiter can gradually destabilize asteroids in this region.
From Science Daily ● Jul. 18, 2026
On April 20, 2025, Lucy passed within 650 miles of Donaldjohanson while traveling through the main asteroid belt on its way to a group of Jupiter Trojan asteroids.
From Science Daily ● Jun. 25, 2026
It will need that money and multiples more to achieve Mr. Musk’s ambition of colonizing Mars and mining asteroids.
From The Wall Street Journal ● Jun. 12, 2026
For one week all of Hyper Base had stopped dead, barring some paper work on the subsidiary asteroids of the group.
From "I, Robot" by Isaac Asimov
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
