There are millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun 's solar nebula that never grew large enough to become planets. The large majority of known asteroids orbit in the asteroid belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter (the Jupiter trojans). However, other orbital families exist with significant populations, including the near - Earth objects. Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C - type, M - type, and S - type. These were named after and are generally identified with carbon - rich, metallic, and silicate (stony) compositions, respectively. The size of asteroids varies greatly, the largest is almost 1,000 km (625 mi) across.
relatively small bodies which generally orbit the sun between mars and jupiter are called
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