Asteroid

Introduction
Major milestones in asteroid research
- Early discoveries
- Later advances
Geography of the asteroid belt
- Names and orbits of asteroids
- Distribution and Kirkwood gaps
- Near-Earth asteroids
- Main-belt asteroid families
- Hungarias and outer-belt asteroids
- Trojan asteroids
Asteroids in unusual orbits
Asteroids as individual worlds
Classification of asteroids
Physical characteristics of asteroids
- Rotation and shape
- Size and albedo
- Mass and density
- Composition
Spacecraft exploration
Origin and evolution of the asteroids

References & Edit History Quick Facts & Related Topics

Images & Videos

Illustration showing a massive asteroid above a city map with a dinosaur silhouette for scale, highlighting the asteroid's size compared to major urban areas.

Graph showing the distribution of asteroids in the solar system by distance from the Sun, with peaks representing concentrations in the main belt and gaps at certain orbital resonances with Jupiter. Colored lines below indicate the percentage of major asteroid classes-E, S, M, C, and P-at various distances. Mars and Jupiter are marked at 1.5 and 5.2 AU, respectively.

At a Glance

asteroid summary

Quizzes

The orbits of the planets and other elements of the solar system, including asteroids, Kuiper belt, Oort cloud, comet

Space Odyssey

1 July 2002: The Solar and Heliospheric Observatory (SOHO) satellite reveals a massive solar eruption more than 30 times the Earth's diameter. The eruption formed when a loop of a magnetic field over the surface of the Sun trapped hot gas.

Brightest Star in the Solar System

Nicolaus Copernicus. Nicolas Copernicus (1473-1543) Polish astronomer. In 1543 he published, forward proof of a Heliocentric (sun centered) universe. Coloured stipple engraving published London 1802. De revolutionibus orbium coelestium libri vi.

All About Astronomy

Related Questions

How are asteroid classes identified from reflected sunlight?
How are eucrite meteorites connected to Vesta?
How can asteroid fragments enter Earth-crossing orbits?
How can meteorites reveal the history of the early solar system?
How can stellar occultations measure an asteroid’s size?
How did Jupiter’s gravity affect the asteroid belt?
How did giant-planet migration mix material in the asteroid belt?
How did radioactive isotopes heat some early asteroids?
How did some asteroids develop metal cores and basaltic surfaces?
How did the Chicxulub impact affect life at the end of the Cretaceous Period?
How did the DART mission change Dimorphos’s orbit?
How did the Vredefort impact crater form in South Africa?
How do Trojan asteroids differ from asteroids in the main belt?
How do asteroid impacts create craters on planets and moons?
How does a meteoroid become a meteor?
How does an asteroid’s albedo affect its apparent brightness?
How does radar reveal the shapes of near-Earth asteroids?
How does thermal radiometry help astronomers estimate asteroid sizes?
How large is Ceres compared with other asteroids?
How long does Vesta take to orbit the Sun?
How was Pallas discovered?
What are near-Earth asteroids?
What caused the Chelyabinsk explosion over Russia in 2013?
What did the Dawn spacecraft discover about Vesta?
What happened during the Tunguska event in 1908?
What materials are found on C-class asteroids?
What minerals are found on S-class asteroids?
Where are Trojan asteroids found in the solar system?
Where is the main asteroid belt located?
Which asteroid classes have the darkest surfaces?
Which asteroids are the largest in the asteroid belt?
Why are V-class asteroids linked to basaltic meteorites?
Why are asteroids also called minor planets?
Why can some near-Earth asteroids pose an impact hazard to Earth?
Why do asteroid albedos vary so widely?
Why do asteroid orbits change near gravitational resonances with Jupiter?
Why do most meteorites found on Earth come from asteroids?
Why do some asteroids contain hydrated minerals?
Why is Ceres classified as a dwarf planet?
Why is Vesta considered a protoplanet?
Why might M-class asteroids contain nickel-iron metal?

Science Astronomy

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External Websites

The Nine Planets - Asteroid Facts
Lunar and Planetary Institute - Asteroids: New Challenges, New Targets
National Center for Biotechnology Information - PubMed Central - No exotic matter in asteroids
University of Central Florida Pressbooks - Asteroids
NASA - Asteroids
CUNY Pressbooks Network - Introduction to Planetary Geology - Asteroids
LiveScience - What are asteroids?
Space.com - Asteroids: Fun facts and information about these space rocks
K12 LibreTexts - Asteroids

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

asteroid - Children's Encyclopedia (Ages 8-11)
asteroid - Student Encyclopedia (Ages 11 and up)

Asteroid

astronomy

Also known as: minor planet, planetoid

Written by

Edward F. Tedesco

Research Associate Professor, Space Science Center, University of New Hampshire, Durham.

Edward F. Tedesco

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 11, 2026 •History

Asteroid, any of a host of small bodies, about 1,000 km (600 miles) or less in diameter, that orbit the Sun primarily between the orbits of Mars and Jupiter in a nearly flat ring called the asteroid belt. It is because of their small size and large numbers relative to the major planets that asteroids are also called minor planets. The two designations have been used interchangeably, though the term asteroid is more widely recognized...

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