Asteroid

Article By:

Chapman, Clark R. Planetary Science Institute, Tucson, Arizona.

Last reviewed:June 2022

DOI:https://doi.org/10.1036/1097-8542.056500

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• Asteroid, published November 2019:Download PDF Get Adobe Acrobat Reader

One of the many hundreds of thousands of small planets (technically called minor planets) revolving around the Sun, mainly between the orbits of Mars and Jupiter. Asteroids are rocky bodies varying greatly in size from less than 10 meters across (33 feet) to about 530 km (330 miles) across in the case of the largest asteroid, Vesta (Fig. 1). Unlike planets, asteroids are irregularly shaped and nonspherical because they do not possess enough mass to generate sufficient gravity to pull themselves into hydrostatic equilibrium. Asteroid surfaces also characteristically display many impact craters. This heavy cratering is indicative of the old age of asteroids, with most of the bodies dating back to the formation of our solar system 4.6 billion years ago. Asteroids are the remnants of the planet formation process, representing material that did not end up comprising a planet or moon. Asteroids are also present in exosolar systems, evidencing the general universality of planetary formation. See also: Gravity; Mass; Planet; Solar system; Vesta

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