The smaller objects in the solar system are called planetoids or asteroids. They are much smaller and have less mass than planets. They are referred to as planetoids or asteroids
Most of them follow circular paths around the Sun between the paths of Mars and Jupiter. The area is called the asteroid_belt. All of the objects there collectively would not even equal the size of the Moon.
The orbits of many of these objects cross the path of Mars and the Earth (e.g. Apollo and Toro). Some travel even closer to the Sun than Mercury (Icarus, a member of the Apollo family). A special group, called the Trojans, travels at a constant distance to each side of Jupiter and follows its path around the Sun. It is thought that the planet, with its great mass, prevented these objects from forming a larger object.
Most of the planetoids are between 300 and 500 million kilometers from the Sun. One group consists of the dark objects, rich in carbon and with irregular shapes. Another group has objects made up of rock with a metal core. The objects of a third group are chunks of metal, made up of iron and nickel.
The scholar Johannes Kepler (1571-1630) presumed the existence of another object between Mars and Jupiter. The first planetoid, which was named Ceres, was discovered in 1801. Today, over 4000 asteroids have been examined closely and it is known that millions more exist.
Ceres was named after a Roman goddess. It has a diameter of approximately 1000 kilometers, which makes it the largest of the asteroids. It is covered in dark dust and reflects very little light from the Sun.
With its diameter of 570 kilometers, Pallas is the second largest asteroid, followed by Vesta with 539 kilometers. Vesta has a strongly reflecting surface and for this reason is visible to the naked eye.
None of the small, irregular objects has any atmosphere.
