any of a host of rocky 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...

Asteroids are small bodies in space—the numerous leftover planetesimals from which the planets were made nearly 4.6 billion years ago. Most are in the "main belt," which is a doughnut-like volume of space between Mars and Jupiter...

For much of history, the solar system was thought to consist of large objects: Earth, the Moon, the Sun, and other planets. However, within the last two centuries astronomers have discovered a menagerie of small objects throughout the solar system,...

Johannes Kepler was the first to postulate the existence of a hidden planet between Mars and Jupiter, a theory long pondered by astronomers. Then, in 1766, Johannes Titius (1729-1796), a professor of mathematics and physics in Germany, developed a...

Asteroids are rocky material left over from the formation of the solar system that orbit the Sun, but are too small to be Asteroid 243 Ida and its moon, photograph. . Reproduced by...

Any of the many rocky small bodies that orbit the Sun mainly in a flat ring, the asteroid belt, between the orbits of Mars and Jupiter. It is thought that the gravitational influence of what became Jupiter kept the asteroids from aggregating into a...

Asteroids, also called minor planets or planetoids, are a class of astronomical objects. The term asteroid is generally used to indicate a diverse group of small celestial bodies in the solar system that orbit around the Sun. 'Asteroid' (Greek for...